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Document and Entity Information - USD ($) $ in Millions	12 Months Ended
Document and Entity Information - USD ($) $ in Millions	Dec. 31, 2017	Mar. 23, 2018	Jun. 30, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	Enphase Energy, Inc.
Entity Central Index Key	0001463101
Document Type	10-K
Document Period End Date	Dec. 31, 2017
Amendment Flag	false
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Smaller Reporting Company
Entity Common Stock, Shares Outstanding		95,829,245
Entity Well-Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 49.9

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 29,144	$ 17,764
Accounts receivable, net of allowances of $2,378 and $2,921 at December 31, 2017 and 2016, respectively	65,346	61,019
Inventory	25,999	31,960
Prepaid expenses and other	9,957	7,121
Total current assets	130,446	117,864
Property and equipment, net	26,483	31,440
Goodwill	3,664	3,664
Intangibles, net	515	945
Other assets	8,039	9,663
Total assets	169,147	163,576
Current liabilities:
Accounts payable	28,747	31,696
Accrued liabilities	22,447	22,937
Deferred revenues	15,691	6,411
Warranty obligations, current portion (includes $2,240 and $3,296 measured at fair value at December 31, 2017 and 2016, respectively)	7,427	8,596
Revolving credit facility	0	10,100
Debt, current	17,429	3,032
Total current liabilities	91,741	82,772
Deferred revenues, non-current	29,941	33,893
Warranty obligations, non-current (includes $7,551 and $7,036 measured at fair value at December 31, 2017 and 2016, respectively)	22,389	22,818
Other non-current liabilities	1,880	2,025
Debt, less current portion	32,322	20,768
Total liabilities	178,273	162,276
Commitments and contingencies
Stockholders’ (deficit) equity:
Preferred stock, $0.00001 par value, 10,000 shares authorized; none issued and outstanding	0	0
Common stock, $0.00001 par value, 125,000 and 100,000 shares authorized and 85,914 and 62,269 shares issued and outstanding at December 31, 2017 and 2016, respectively	1	1
Additional paid-in capital	287,256	252,126
Accumulated deficit	(295,727)	(250,535)
Accumulated other comprehensive loss	(656)	(292)
Total stockholders’ (deficit) equity	(9,126)	1,300
Total liabilities and stockholders’ (deficit) equity	$ 169,147	$ 163,576

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Allowances, accounts receivable	$ 2,378	$ 2,921
Warrant obligations at fair value, current	2,240	3,296
Warrant obligations at fair value, noncurrent	$ 7,551	$ 7,036
Preferred stock, par value (usd per share)	$ 0.00001	$ 0.00001
Preferred stock, shares authorized (shares)	10,000,000	10,000,000
Preferred stock, shares issued (shares)	0	0
Preferred stock, shares outstanding (shares)	0	0
Common stock, par value (usd per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized (shares)	125,000,000	100,000,000
Common stock, shares issued (shares)	85,914,000	62,269,000
Common stock, shares outstanding (shares)	85,914,000	62,269,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Statement [Abstract]
Net revenues	$ 286,166	$ 322,591	$ 357,249
Cost of revenues	230,123	264,583	249,032
Gross profit	56,043	58,008	108,217
Operating expenses:
Research and development	33,157	50,703	50,819
Sales and marketing	23,126	38,810	45,877
General and administrative	22,221	27,418	30,830
Restructuring and other charges	16,917	3,777	0
Total operating expenses	95,421	120,708	127,526
Loss from operations	(39,378)	(62,700)	(19,309)
Other income (expense):
Interest expense	(7,936)	(2,773)	(501)
Other income (expense), net	1,973	(514)	(893)
Total other expense, net	(5,963)	(3,287)	(1,394)
Loss before income taxes	(45,341)	(65,987)	(20,703)
Benefit (provision) for income taxes	149	(1,475)	(1,379)
Net loss	$ (45,192)	$ (67,462)	$ (22,082)
Net loss per share, basic and diluted (usd per share)	$ (0.54)	$ (1.34)	$ (0.49)
Shares used in computing net loss per share, basic and diluted (shares)	82,939	50,519	44,632

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Comprehensive Income [Abstract]
Net loss	$ (45,192)	$ (67,462)	$ (22,082)
Other comprehensive loss:
Foreign currency translation adjustments	(364)	(82)	(131)
Other comprehensive loss:	(364)	(82)	(131)
Comprehensive loss	$ (45,556)	$ (67,544)	$ (22,213)

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
BALANCE, Beginning at Dec. 31, 2014	$ 46,952	$ 0	$ 208,022	$ (160,991)	$ (79)
BALANCE, Beginning (shares) at Dec. 31, 2014		43,756
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans	4,014		4,014
Issuance of common stock under employee stock plans (shares)		2,065
Stock-based compensation	12,696		12,696
Net loss	(22,082)			(22,082)
Foreign currency translation adjustment	(131)				(131)
BALANCE, Ending at Dec. 31, 2015	41,449	$ 0	224,732	(183,073)	(210)
BALANCE, Ending (shares) at Dec. 31, 2015		45,821
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans	1,145	$ 1	1,144
Issuance of common stock under employee stock plans (shares)		1,498
Issuance of common stock, net of offering costs	15,924		15,924
Issuance of common stock, net of offering costs (shares)		14,950
Stock-based compensation	10,326		10,326
Net loss	(67,462)			(67,462)
Foreign currency translation adjustment	(82)				(82)
BALANCE, Ending at Dec. 31, 2016	1,300	$ 1	252,126	(250,535)	(292)
BALANCE, Ending (shares) at Dec. 31, 2016		62,269
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans	531		531
Issuance of common stock under employee stock plans (shares)		1,752
Issuance of common stock, net of offering costs	26,425		26,425
Issuance of common stock, net of offering costs (shares)		21,893
Issuance of warrants	1,447		1,447
Stock-based compensation	6,727		6,727
Net loss	(45,192)			(45,192)
Foreign currency translation adjustment	(364)				(364)
BALANCE, Ending at Dec. 31, 2017	$ (9,126)	$ 1	$ 287,256	$ (295,727)	$ (656)
BALANCE, Ending (shares) at Dec. 31, 2017		85,914

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating activities:
Net loss	$ (45,192)	$ (67,462)	$ (22,082)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Depreciation and amortization	9,004	10,638	10,539
Provision for doubtful accounts	476	3,097	1,502
Asset impairment and restructuring	1,681	3,190	522
Gain on business divestiture	0	(640)	0
Amortization of debt issuance costs	1,673	145	163
Stock-based compensation	6,727	10,326	12,696
Revaluation of contingent consideration liability	0	0	(1,827)
Deferred income tax (benefit) expense	(1,394)	651	642
Changes in operating assets and liabilities (net of acquisition/divestiture):
Accounts receivable	(4,803)	(18,017)	(2,482)
Inventory	5,961	8,840	(19,210)
Prepaid expenses and other assets	(1,227)	(4,759)	(5,281)
Accounts payable, accrued and other liabilities	(5,078)	8,897	(2,620)
Warranty obligations	(1,598)	867	(3,393)
Deferred revenues	5,328	11,274	9,671
Net cash used in operating activities	(28,442)	(32,953)	(21,160)
Investing activities:
Purchases of property and equipment	(4,121)	(12,167)	(12,525)
Purchases of intangible assets	0	(678)	(237)
Business divestitures	0	1,050	0
Change in restricted cash	0	0	300
Net cash used in investing activities	(4,121)	(11,795)	(12,462)
Financing activities:
Proceeds from common stock offerings, net of issuance costs	26,425	16,142	0
Proceeds from debt, net of issuance costs	26,442	23,989	0
Proceeds from borrowings under revolving credit facility	0	10,000	46,000
Payments under revolving credit facility	(10,100)	(16,900)	(29,150)
Holdback payment related to prior acquisition	0	0	(300)
Proceeds from issuance of common stock under employee stock plans	530	1,144	4,014
Net cash provided by financing activities	43,297	34,375	20,564
Effect of exchange rate changes on cash	646	(315)	(522)
Net increase (decrease) in cash and cash equivalents	11,380	(10,688)	(13,580)
Cash and cash equivalents — Beginning of year	17,764	28,452	42,032
Cash and cash equivalents — End of year	29,144	17,764	28,452
Supplemental cash flow disclosure:
Cash paid for interest	5,816	2,704	358
Cash paid for income taxes	909	1,146	594
Noncash financing and investing activities:
Offering and loan costs included in accrued liabilities	0	518	0
Purchases of fixed and intangible assets included in accounts payable	$ 551	$ 700	$ 1,718

DESCRIPTION OF BUSINESS	12 Months Ended
DESCRIPTION OF BUSINESS	Dec. 31, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS	DESCRIPTION OF BUSINESS Enphase Energy, Inc. and subsidiaries (the “Company”) delivers simple, innovative and reliable energy management solutions that advance the worldwide potential of renewable energy. The Company’s semiconductor-based microinverter system converts direct current (DC) electricity to alternating current (AC) electricity at the individual solar module level, and brings a system-based, high technology approach to solar energy generation leveraging our design expertise across power electronics, semiconductors, networking, and cloud-based software technologies. Since inception, the Company has shipped more than 16 million microinverters, representing over 3 gigawatts of solar photovoltaic (PV) generating capacity, and more than 739,000 Enphase residential and commercial systems have been deployed in over 110 countries.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

Basis of Presentation and Consolidation

The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (“US GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.

The Company has taken and continues to take actions to improve its financial stability. Such actions include accessing additional capital, reducing its operating expense structure and substantially transitioning to its next generation of microinverters, which offer increased functionality and have a reduced cost profile.

The restructuring actions taken by the Company resulted in a $38.4 million reduction in ongoing operating expenses (excluding restructuring charges of $16.9 million and $3.8 million for the years ended December 31, 2017 and 2016, respectively) for the year ended December 31, 2017 as compared to 2016.

In February of 2018 the Company raised an additional $20.0 million through a private placement of the Company’s common stock and also reached an agreement with its lender to defer approximately 50% of the principal payments due in 2018 under its term loans, with the deferred principal being amortized over the remaining term of the loan.

The Company’s management has considered the factors noted above and has concluded that substantial doubt as to its ability to continue as a going concern does not exist at the time of filing its Annual Report on Form 10-K for the period ended December 31, 2017.

Use of Estimates

The preparation of the Company’s consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. These estimates are based on information available as of the date of the financial statements; therefore, actual results could differ materially from management’s estimates using different assumptions or under different conditions.

Revenue Recognition

The Company generates revenue from sales of its microinverter systems, which include microinverter units and related accessories, an Envoy communications gateway, the cloud-based Enlighten monitoring service, and AC Battery storage solutions to distributors, large installers, OEMs and strategic partners. Enlighten service revenue represented less than 2% of the total revenues for all periods presented.

Revenue from sales of the Company’s products is recognized when: (i) persuasive evidence of an arrangement exists; (ii) delivery of the products has occurred in accordance with the terms of the sales agreement and title and risk of loss have passed to the customer; (iii) the sale price is fixed or determinable; and (iv) collection is reasonably assured. Provisions for rebates, sales incentives, and discounts to customers are accounted for as reductions in revenue in the same period the related sales are recorded.

Sales of an Envoy communications gateway include the Enlighten cloud-based monitoring service. The allocation of revenue between the two deliverables is based on the Company’s best estimate of selling price determined by considering multiple factors including internal costs, gross margin and historical pricing practices. After allocating the overall consideration from such sale to each deliverable using a best estimate of the selling price, revenue from the sale of Envoy hardware devices is recognized upon shipment, assuming all other revenue recognition criteria have been met. Through September 30, 2017 the estimated economic life of the related Envoy devices was used to determine the period over which revenue from the cloud-based monitoring service was recognized as adequate historical user data was not available. During the fourth quarter of 2017 the Company determined historical user data was available to adequately assess the period over which the service obligation was met. As a result, the Company shortened the estimated service period of the Enlighten from 10 years to 6.5 years effective October 1, 2017. The impact of the change is estimate was an increase to revenue and earnings in the fourth quarter of 2017 of approximately $2.6 million and a reduction of net loss per share of approximately $0.03.

Deferred revenues consist of payments received from customers in advance of revenue recognition for the Company’s products and services as described above. As of December 31, 2017 and 2016, deferred revenues consist primarily of Enlighten service revenue.

Cost of Revenues

The Company includes the following in cost of revenues: product costs, warranty, manufacturing personnel and logistics costs, freight costs, inventory write-downs, hosting services costs related to the Company’s Enlighten service offering, and depreciation and amortization of manufacturing test equipment.

Cash and Cash Equivalents

The Company considers all highly liquid investments, such as certificates of deposit and money market instruments with maturities of three months or less at the time of acquisition to be cash equivalents. For all periods presented, its cash balances consist of amounts held in non-interest-bearing deposits and money market accounts.

Fair Value of Financial Instruments

The carrying amounts of the Company’s cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value because of the short maturity of those instruments.

Allowances for Doubtful Accounts

The Company maintains allowances for doubtful accounts for uncollectible accounts receivable. Management estimates anticipated losses from doubtful accounts based on days past due, collection history and the financial health of customers. The allowance for doubtful accounts was $2.4 million and $2.9 million at December 31, 2017 and 2016, respectively. The following table sets forth activities in the allowance for doubtful accounts for the periods indicated (in thousands):



	December 31,
	2017			2016			2015
Balance, at beginning of year	$	2,921		$	1,808		$	569
Net charges to expenses	476			3,097			1,502
Write-offs, net of recoveries	(1,019		)	(1,984		)	(263		)
Balance, at end of year	$	2,378		$	2,921		$	1,808

Inventory

Inventory is valued at the lower of cost or market. Market is current replacement cost (by purchase or by reproduction, dependent on the type of inventory). In cases where market exceeds net realizable value (i.e., estimated selling price less reasonably predictable costs of completion and disposal), inventories are stated at net realizable value. Market is not considered to be less than net realizable value reduced by an allowance for an approximately normal profit margin. The Company determines cost on a first-in first-out basis. Management assesses the valuation on a quarterly basis and writes down the value for any excess and obsolete inventory based upon expected demand, anticipated sales price, effect of new product introductions, product obsolescence, customer concentrations, product merchantability and other factors. Inventory write-downs are equal to the difference between the cost of inventories and market.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation. Cost includes amounts paid to acquire or construct the asset as well as any expenditure that substantially adds to the value of or significantly extends the useful life of an existing asset. Repair and maintenance costs are expensed as incurred. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the assets, which range from three to ten years. Leasehold improvements are amortized over the shorter of the lease term or expected useful life of the improvements.

Capitalized Software Costs

Internally used software, whether purchased or developed, is capitalized and amortized on a straight-line basis over its estimated useful life. Costs associated with internally developed software are expensed until the point at which the project has reached the development stage. Subsequent additions, modifications or upgrades to internal-use software are capitalized only to the extent that they provide additional functionality. Software maintenance and training costs are expensed in the period in which they are incurred. The capitalization of software requires judgment in determining when a project has reached the development stage and the period over which the Company expects to benefit from the use of that software.

Long-Lived Assets

Property, plant and equipment, including capitalized software costs, are recorded at cost. Property, plant and equipment amounts are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (asset group) may not be recoverable. An impairment loss would be recognized when the carrying amount of an asset exceeds the estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition. The amount of the impairment loss to be recorded is calculated by the excess of the asset's carrying value over its fair value. Fair value is generally determined using a discounted cash flow analysis. The Company recorded asset impairment charges for specific assets that were no longer in use of approximately $0.8 million and $2.6 million for the years ended December 31, 2017 and 2016, respectively. The fair value of the remaining assets is in excess of the carrying value.

Goodwill

Goodwill results from the purchase consideration paid in excess of the fair value of the net assets recorded in connection with a business acquisition. Goodwill is not amortized, but is assessed for potential impairment at least annually during the fourth quarter of each fiscal year or between annual tests if an event occurs or circumstances change that would indicate the carrying amount may be impaired. Goodwill is tested at the reporting unit level, which the Company has determined to be the same as the entity as a whole (entity level). Once goodwill has been assigned to a reporting unit, it is no longer associated with a particular acquisition; therefore, all of the activities within a reporting unit, whether acquired or organically grown, are available to support the goodwill value. Based on management’s goodwill impairment tests, there was no impairment of goodwill in any of the years presented.

Intangible Assets

Intangible assets include patents and other purchased intangible assets. Intangible assets with finite lives are amortized on a straight-line basis, with estimated useful lives ranging from 3 to 5 years. Indefinite-lived intangible assets are tested for impairment annually and are also tested for impairment between annual tests if an event occurs or circumstances change that would indicate that the carrying amount may be impaired. Intangible assets with finite lives are tested for impairment whenever events or circumstances indicate that the carrying amount of an asset (asset group) may not be recoverable. An impairment loss is recognized when the carrying amount of an asset exceeds the estimated undiscounted cash flows used in determining the fair value of the asset. The amount of the impairment loss to be recorded is calculated by the excess of the asset's carrying value over its fair value. Fair value is generally determined using a discounted cash flow analysis. There was no impairment of intangible assets in any of the years presented.

Warranty Obligations

Microinverters Sold Through December 31, 2013

The Company’s warranty accrual provides for the replacement of microinverter units that fail during the product’s warranty term (15 years for first and second generation microinverters and up to 25 years for third and fourth generation microinverters). On a quarterly basis, the Company employs a consistent, systematic and rational methodology to assess the adequacy of its warranty liability. This assessment includes updating all key estimates and assumptions for each generation of product, based on historical results, trends and the most current data available as of the filing date. The key estimates and assumptions used in the warranty liability are thoroughly reviewed by management on a quarterly basis. The key estimates used by the Company to estimate its warranty liability are: (1) the number of units expected to fail over time (i.e. failure rate); (2) the number of failed units expected to result in warranty claims over time (i.e. claim rate); and (3) the per unit cost of replacement units, including outbound shipping and limited labor costs, expected to be incurred to replace failed units over time (i.e. replacement cost).

Estimated Failure Rates—The Company’s Quality and Reliability department has primary responsibility to determine the estimated failure rates for each generation of microinverter. To establish initial failure rate estimates for each generation of microinverter, the Company’s quality engineers use a combination of industry standard MTBF (Mean Time Between Failure) estimates for individual components contained in its microinverters, third party data collected on similar equipment deployed in outdoor environments similar to those in which the Company’s microinverters are installed, and rigorous long term reliability and accelerated life cycle testing which simulates the service life of the microinverter in a short period of time. As units are deployed into operating environments, the Company continues to monitor product performance via its Enlighten monitoring platform. It typically takes three to nine months between the date of sale and date of end-user installation. Consequently, the Company’s ability to monitor actual failures of units sold similarly lags by three to nine months. When a microinverter fails and is returned, the Company performs diagnostic root cause failure analysis to understand and isolate the underlying mechanism(s) causing the failure. The Company then uses the results of this analysis (combined with the actual, cumulative performance data collected on those units prior to failure via Enlighten) to draw conclusions with respect to how or if the identified failure mechanism(s) will impact the remaining units deployed in the installed base.

Estimated Claim Rates—Warranty claim rate estimates are based upon assumptions with respect to expected customer behavior over the warranty period. As the vast majority of the Company’s microinverters have been sold to end users for residential applications, the Company believes that warranty claim rates will be affected by changes over time in residential home ownership because the Company expects that subsequent homeowners are less likely to file claims than the homeowners who originally purchase the microinverters.

Estimated Replacement Costs—three factors are considered in the Company’s analysis of estimated replacement cost: (1) the estimated cost of replacement microinverters; (2) the estimated cost to ship replacement microinverters to end users; and (3) the estimated labor reimbursement expected to be paid to third party installers performing replacement services for the end user. Because the Company’s warranty provides for the replacement of defective microinverters over long periods of time (between 15 and 25 years, depending on the generation of product purchased), the estimated per unit cost of current and future product generations is considered in the estimated replacement cost. Estimated costs to ship replacement units are based on observable, market-based shipping costs paid by the Company to third party freight carriers. The Company has a separate program that allows third-party installers to claim fixed-dollar reimbursements for labor costs they incur to replace failed microinverter units for a limited time from the date of original installation. Included in the Company’s estimated replacement cost is an analysis of the number of fixed-dollar labor reimbursements expected to be claimed by third party installers over the limited offering period.

In addition to the key estimates noted above, the Company also compares actual warranty results to expected results and evaluates any significant differences. Management may make additional adjustments to the warranty provision based on performance trends or other qualitative factors. If actual failure rates, claim rates, or replacement costs differ from the Company’s estimates in future periods, changes to these estimates may be required, resulting in increases or decreases in the Company’s warranty obligations. Such increases or decreases could be material.

Fair Value Option for Microinverters Sold Since January 1, 2014

The Company’s warranty obligations related to microinverters sold since January 1, 2014 provide the Company the right, but not the requirement, to assign its warranty obligations to a third-party. Under Accounting Standards Codification (“ASC”) 825—Financial Instruments, (“fair value option”), an entity may choose to elect the fair value option for such warranties at the time it first recognizes the eligible item. The Company made an irrevocable election to account for all eligible warranty obligations associated with microinverters sold since January 1, 2014 at fair value. This election was made to reflect the underlying economics of the time value of money for an obligation that will be settled over an extended period of up to 25 years.

The Company estimates the fair value of warranty obligations by calculating the warranty obligations in the same manner as for sales prior to January 1, 2014 and applying an expected present value technique to that result. The expected present value technique, an income approach, converts future amounts into a single current discounted amount. In addition to the key estimates of failure rates, claim rates and replacement costs, the Company used certain inputs that are unobservable and significant to the overall fair value measurement. Such additional assumptions included compensation comprised of a profit element and risk premium required of a market participant to assume the obligation and a discount rate based on the Company’s credit-adjusted risk-free rate. See Note 8, (“Fair Value Measurements”) for additional information.

Warranty obligations initially recorded at fair value at the time of sale will be subsequently re-measured to fair value at each reporting date. In addition, the fair value of the liability will be accreted over the corresponding term of the warranty of up to 25 years using the interest method.

Warranty for Other Products

The Company offers a 5 year warranty for its Envoy communications gateway and a 10 year warranty on its AC Battery storage solution. The warranties provide the Company with the right, but not the obligation, to assign its warranty obligations to a third-party. As such, warranties for Envoy and AC Battery storage solution products are accounted for under the fair value method of accounting.

Research and Development Costs

The Company expenses research and development costs as incurred. Research and development costs totaled $33.2 million, $50.7 million and $50.8 million in 2017, 2016 and 2015, respectively.

Stock-Based Compensation

Share-based payments are required to be recognized in the Company’s consolidated statements of operations based on their fair values and the estimated number of shares expected to vest. The Company measures stock-based compensation expense for all share-based payment awards, including stock options made to employees and directors, based on the estimated fair values on the date of the grant. The fair value of stock options granted is estimated using the Black-Scholes option valuation model. The fair value of restricted stock units granted is determined based on the price of the Company’s common stock on the date of grant. Stock-based compensation, net of estimated forfeitures, is recognized on a straight-line basis over the requisite service period, which is typically four years.

Comprehensive Loss

Comprehensive loss consists of two components, net loss and other comprehensive income (loss). Other comprehensive income (loss) refers to gains and losses that are recorded as an element of stockholders’ equity but are excluded from net income. The Company’s other comprehensive income (loss) consists of foreign currency translation adjustments for all periods presented.

Income Taxes

The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected tax consequences of temporary differences between the tax bases of assets and liabilities for financial reporting purposes and amounts recognized for income tax purposes. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized.

The Company operates in various tax jurisdictions and is subject to audit by various tax authorities. The Company follows accounting for uncertainty in income taxes which requires that the tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes.

Recently Adopted Accounting Pronouncements

In July 2015, the FASB issued ASU 2015-11, “Simplifying the Measurement of Inventory,” which requires most entities to measure most inventories at the lower of cost or net realizable value ("NRV"). This simplifies the evaluation from the current method of lower of cost or market, where market is based on one of three measures (i.e. replacement cost, net realizable value, or net realizable value less a normal profit margin). ASU 2015-11 does not apply to inventories measured under the last-in, first-out method or the retail inventory method, and defines NRV as the “estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation.” This standard, which was adopted in the first quarter of 2017, did not have a material impact on the consolidated financial statements.

In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting,” which will simplify the income tax consequences, accounting for forfeitures and classification on the Statements of Consolidated Cash Flows. This standard, which was adopted in the first quarter of 2017, did not have a material impact on the consolidated financial statements.

In January 2017, the FASB issued ASU 2017-04, “Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” This ASU simplifies the subsequent measurement of goodwill, the FASB eliminated Step 2 from the goodwill impairment test. Under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The FASB also eliminated the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. Therefore, the same impairment assessment applies to all reporting units. An entity is required to disclose the amount of goodwill allocated to each reporting unit with a zero or negative carrying amount of net assets. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. A public business entity that is an SEC filer should adopt the amendments in this Update for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. ASU 2017-04 was early adopted by the Company for the year beginning January 1, 2017. The Company has a single reporting unit, and adoption of the standard did not have a material impact on the Company's consolidated financial statements.

Recent Accounting Pronouncements Not Yet Effective

In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606 and issued subsequent amendments to the initial guidance in August 2015, March 2016, April 2016, May 2016 and December 2016, collectively “Topic 606”). Topic 606 supersedes nearly all existing revenue recognition guidance under GAAP. The standard is effective for and was adopted by the Company on January 1, 2018.

The updated standard’s core principle is that revenue is recognized when the customer obtains control of promised goods or services in an amount that reflects the consideration to which an entity expects to be received in exchange for those goods or services. The standard generally requires an entity to identify performance obligations in its contracts, estimate the amount of variable consideration to be received in the transaction price, allocate the transaction price to each separate performance obligation, and recognize revenue as obligations are satisfied. In addition, the updated standard requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts.

The guidance permits two methods of adoption, the full retrospective method applying the standard to each prior reporting period presented, or the modified retrospective method with a cumulative effect of initially applying the guidance recognized at the date of initial application. The Company will adopt the standard using the modified retrospective method with a cumulative catch up adjustment to accumulated deficit and will provide additional disclosures comparing results to previous GAAP in its 2018 consolidated financial statements.

The most significant impacts upon adoption of the standard will be how the Company accounts for revenue related to its envoy communications device and related enlighten service and the timing of when certain sales incentives will be recognized. Under ASC 605 the Company’s monitoring hardware and service are considered two units of accounting with a portion of the consideration related to the hardware recognized upfront and the remaining deferred over the estimated service period. Under ASC 606 the full consideration for these products represents a single performance obligation and is deferred over the estimated service period. This treatment will result in an increase in deferred revenue of approximately $77 million, an increase in deferred costs of approximately $43 million and an increase in accumulated deficit of approximately $34 million upon adoption of ASC 606.

Under ASC 605 the Company recorded certain contra revenue promotions at the later of the date revenue was recognized or the date at which the promotional offer was extended. Under ASC 606 all such contra revenue programs will be treated as variable consideration and recognized at the time the related revenue is recorded. This change in timing will result in an increase in accrued liabilities of approximately $6 million and an increase to accumulated deficit in the same amount upon adoption of ASC 606. The change in accounting treatment affects the timing of the recognition of certain contra revenue programs, but the overall income statement impact of this new accounting method is expected to be immaterial.

Under ASC 605, the Company expensed commission costs as incurred. The new standard requires upfront contract acquisition costs, such as sales commissions, to be capitalized and amortized over the estimated life of the asset. Under the new guidance, the Company will utilize the practical expedient permitting expensing of costs to obtain a contract when the expected amortization period is one year or less, which typically results in expensing commissions paid. Commissions related to the Company’s sale of monitoring hardware and service will be capitalized and amortized over the period of the associated revenue, which is 6.5 years. This treatment will result in an increase in deferred costs of approximately $0.8 million and an increase in accumulated deficit by the same amount upon adoption of ASC 606. The amortization of these deferred costs is immaterial to the Company’s income statement.

The Company does not expect the adoption of ASC 606 to have a material impact on the amount or timing of revenue recognition related to specific customer contracts.

In January 2016, the FASB issued ASU 2016-01, “Recognition and Measurement of Financial Assets and Financial Liabilities,” which amends certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Changes to the current guidance include the accounting for equity investments, the presentation and disclosure requirements for financial instruments, and the assessment of valuation allowance on deferred tax assets related to available-for-sale securities. In addition, ASU 2016-01 establishes an incremental recognition and disclosure requirement related to the presentation of fair value changes of financial liabilities for which the fair value option has been elected. Under this guidance, an entity would be required to separately present in other comprehensive income the portion of the total fair value change attributable to instrument-specific credit risk as opposed to reflecting the entire amount in earnings. ASU 2016-01 is effective for fiscal years and interim periods beginning after December 15, 2017, and upon adoption, an entity should apply the amendments by means of a cumulative-effect adjustment to the balance sheet at the beginning of the first reporting period in which the guidance is effective. Early adoption is not permitted except for the provision to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. The Company does not expect the adoption of this standard to have a material impact on the consolidated financial statements.

In February 2016, the FASB issued Accounting Standards Codification (“ASC”) 842 (“ASC 842”), “Leases” which replaces the existing guidance in ASC 840, Leases. ASC 842 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. ASC 842 requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use (ROU) asset and a corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the ROU asset and for operating leases the lessee would recognize a straight-line total lease expense. The Company is currently evaluating the impact of adoption on the consolidated financial statements.

In November 2016, the FASB issued Accounting Standards Update No. 2016-18 (ASU 2016-18), “Statement of Cash Flows,” which requires companies to include amounts generally described as restricted cash and restricted cash equivalents in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements.

In May 2017, the FASB issued ASU 2017-09 (ASU 2017-09), "Compensation - Stock Compensation." ASU 2017-09 was issued to provide clarity and reduce both 1) diversity in practice and 2) cost and complexity when applying the guidance in Topic 718 to a change in the terms or conditions of a share-based payment award. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting under Topic 718. ASU 2017-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company is currently evaluating the impact of adoption on the consolidated financial statements.

INVENTORY

12 Months Ended

Dec. 31, 2017

Inventory Disclosure [Abstract]

INVENTORY

Inventory as of December 31, 2017 and 2016, consists of the following (in thousands):



	December 31,
	2017		2016
Raw materials	$	2,341	$	5,095
Finished goods	23,658		26,865
Total inventory	$	25,999	$	31,960

PROPERTY AND EQUIPMENT, NET

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

PROPERTY AND EQUIPMENT, NET

As of December 31, 2017 and 2016, property and equipment consists of the following (in thousands):



	Estimated Useful Life (Years)	December 31,
	Estimated Useful Life (Years)	2017			2016
Equipment and machinery	7-10	$	41,148		$	38,486
Furniture and fixtures	5–7	2,188			2,635
Computer equipment	3–5	2,627			2,913
Capitalized software costs	3–5	11,749			11,324
Leasehold improvements	4–10	8,537			9,477
Construction in process		4,672			6,275
Total		70,921			71,110
Less accumulated depreciation and amortization		(44,438		)	(39,670		)
Property and equipment, net		$	26,483		$	31,440

Depreciation expense for property and equipment was $8.6 million, $10.0 million and $8.1 million, in 2017, 2016 and 2015, respectively.

As of December 31, 2017 and 2016, unamortized capitalized software costs were $1.1 million and $1.9 million, respectively.

GOODWILL AND INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

GOODWILL AND INTANGIBLE ASSETS



	December 31, 2017							December 31, 2016
	Gross		Accumulated Amortization			Net		Gross		Accumulated Amortization			Net
Goodwill	$	3,664	$	—		$	3,664	$	3,664	$	—		$	3,664

Other indefinite-lived intangibles	$	286	$	—		$	286	$	286	$	—		$	286
Intangibles assets with finite lives:
Patents and licensed technology	1,665		(1,436		)	229		1,665		(1,006		)	659
Total purchased intangibles	$	1,951	$	(1,436	)	$	515	$	1,951	$	(1,006	)	$	945

In July 2014, the Company purchased certain patents related to system interconnection and photovoltaic AC module construction. The patents were amortized over their legal life of 3 years. In October 2015, the Company licensed certain technology related to ASIC development for a 3-year term.

The aggregate amortization expense for intangibles assets was $0.4 million, $0.7 million and $0.5 million for the years ended December 31, 2017, 2016 and 2015, respectively. The remaining $0.2 million of patents and licensed technology will be amortized in 2018.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

ACCRUED LIABILITIES

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

ACCRUED LIABILITIES

As of December 31, 2017 and 2016 accrued liabilities consists of the following (in thousands):



	December 31,
	2017		2016
Salaries, commissions, incentive compensation and benefits	$	3,608	$	4,227
Customer rebates and sales incentives	8,988		11,786
Freight	3,853		2,321
Other	5,998		4,603
Total	$	22,447	$	22,937

WARRANTY OBLIGATIONS

12 Months Ended

Dec. 31, 2017

Product Warranties Disclosures [Abstract]

WARRANTY OBLIGATIONS

The Company’s warranty activities during 2017, 2016 and 2015 were as follows (in thousands):



	December 31,
	2017			2016			2015
Balance, at beginning of year	$	31,414		$	30,547		$	33,940
Accruals for warranties issued during the year	3,797			4,130			4,383
Changes in estimates	(732		)	2,562			31
Settlements	(7,037		)	(8,523		)	(7,269		)
Increase due to accretion expense	2,053			1,772			1,001
Fair value adjustments	321			926			(1,539		)
Balance, at end of year	29,816			31,414			30,547
Less current portion	(7,427		)	(8,596		)	(7,072		)
Long-term portion	$	22,389		$	22,818		$	23,475

The Company sold approximately 1.0 million first and second generation microinverters from 2008 through mid-2012. The Company has sold approximately 3.9 million third generation microinverters since mid-2012 through mid-2015. The Company has sold approximately 10.2 million of its fourth generation microinverters, which were introduced in mid-2013 and are still being sold. The Company began selling its IQ series microinverters in 2017, sales of which totaled approximately 1.2 million units.

Changes in Estimates

On a quarterly basis, the Company uses the best and most complete underlying information available, following a consistent, systematic and rational methodology to determine its warranty obligations. The Company considers all available evidence to assess the reasonableness of all key assumptions underlying its estimated warranty obligations for each generation of microinverter. The changes in estimates discussed below resulted from consideration of new or additional information becoming available and subsequent developments. Changes in estimates included in the table above were comprised of the following:

2017

In 2017, primarily in the fourth quarter, the Company recorded the impact of further product-cost reduction initiatives for its sixth generation microinverters, which are backwards compatible with previous microinverter generations and will be used to fulfill future warranty obligations for all microinverter generations in the field. This resulted in a $2.2 million decrease to warranty expense related to estimated future replacement costs. The Company also recorded, primarily in the third quarter, a decrease to warranty expense of $1.9 million for labor reimbursement costs expected to be paid to third party installers performing replacement services for its second generation product as a result of a change in its reimbursement policy. In addition, the Company recorded additional warranty expense of $3.9 million based on continuing analysis of field performance data and diagnostic root-cause failure analysis primarily relating to its second generation product.

2016

In 2016, primarily in the fourth quarter, the Company recorded the impact of product-cost reduction initiatives for its sixth generation microinverters, which are backwards compatible with previous microinverter generations and will be used to fulfill future warranty obligations for all microinverter generations in the field. This resulted in a $2.1 million decrease to warranty expense related to estimated future replacement costs. This decrease was offset by an increase to warranty expense of $1.5 million for an increase in labor reimbursement costs expected to be paid to third party installers performing replacement services for its second generation product. In addition, the Company recorded additional warranty expense of $3.0 million based on continuing analysis of field performance data and diagnostic root-cause failure analysis primarily relating to its second generation product.

2015

In 2015, primarily in the fourth quarter, the Company implemented product-cost reduction initiatives for its fourth generation microinverters, which are backwards compatible with prior microinverter generations and are used to fulfill warranty obligations for all microinverter generations in the field. This resulted in a $1.5 million decrease to warranty expense related to estimated future replacement costs. This decrease was offset by an increase to warranty expense of $0.7 million for an increase in labor reimbursement costs expected to be paid to third party installers performing replacement services for its second generation product. In addition, the Company recorded additional warranty expense of $0.8 million based on continuing analysis of field performance data and diagnostic root-cause failure analysis performed on returned units of its second generation product.

FAIR VALUE MEASUREMENTS

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

FAIR VALUE MEASUREMENTS

The accounting guidance defines fair value as the price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. When determining the fair value measurements for assets and liabilities required to be recorded at fair value, the Company considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability, such as inherent risk, transfer restrictions, and risk of nonperformance.

The fair value hierarchy requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. An asset’s or liability’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Three levels of inputs may be used to measure fair value:


•	Level 1—Valuations based on quoted prices in active markets for identical assets or liabilities that the Company is able to access. Since valuations are based on quoted prices that are readily and regularly available in an active market, valuation of such assets or liabilities do not entail a significant degree of judgment.


•	Level 2—Valuations based on one or more quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly.


•	Level 3—Valuations based on inputs that are unobservable and significant to the overall fair value measurement.

The following table presents the Company’s liabilities that were measured at fair value on a recurring basis and its categorization within the fair value hierarchy at December 31, 2017 and 2016 (in thousands):



		December 31,
	Fair Value Hierarchy	2017		2016
Liabilities:
Warranty obligations	Level 3	$	9,790	$	10,332
Third party option to purchase receivables at a discount	Level 3	700		—

Fair Value Option for Warranty Obligations Related to Microinverters Sold Since January 1, 2014

The Company estimates the fair value of warranty obligations by calculating the warranty obligations in the same manner as for sales prior to January 1, 2014 and applying an expected present value technique to that result. The expected present value technique, an income approach, converts future amounts into a single current discounted amount. In addition to the key estimates of failure rates, claim rates and replacement costs, the Company used certain Level 3 inputs which are unobservable and significant to the overall fair value measurement. Such additional assumptions included a discount rate based on the Company’s credit-adjusted risk-free rate and compensation comprised of a profit element and risk premium required of a market participant to assume the obligation.

The following table provides a reconciliation of the beginning and ending balances of warranty obligations measured at fair value for the periods indicated (in thousands):



Balance—December 31, 2014	$	3,562
Accruals for warranties issued during period	4,140
Changes in estimates	(755		)
Settlements	(227		)
Increase due to accretion expense	1,001
Fair value adjustments	(1,539		)
Balance—December 31, 2015	$	6,182
Accruals for warranties issued during period	4,091
Changes in estimates	(1,616		)
Settlements	(1,023		)
Increase due to accretion expense	1,772
Fair value adjustments	926
Balance—December 31, 2016	$	10,332
Accruals for warranties issued during period	3,591
Changes in estimates	(4,551		)
Settlements	(1,956		)
Increase due to accretion expense	2,053
Fair value adjustments	321
Balance—December 31, 2017	$	9,790

Third Party Option to Purchase Receivables at a Discount

The Company entered into an agreement with a third party in the fourth quarter of 2017 to sell certain current and future receivables at a discount. The buyer has the option to purchase certain additional future receivables at various fixed discounts. This option was valued at $0.7 million using the discounted cash flow methodology based on the counterparty credit-adjusted-risk-free rate and recorded as a liability.

Quantitative and Qualitative Information about Level 3 Fair Value Measurements

As of December 31, 2017, the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows:



Item Measured at Fair Value	Valuation Technique	Description of Significant Unobservable Input	Percent Used (Weighted-Average)
Warranty obligations for microinverters sold since January 1, 2014	Discounted cash flows	Profit element and risk premium	17%
	Discounted cash flows	Credit-adjusted risk-free rate	17%
Third party option to purchase receivables at a discount	Discounted cash flows	Counter party credit-adjusted risk-free rate	4%

As of December 31, 2016, the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows:



Item Measured at Fair Value	Valuation Technique	Description of Significant Unobservable Input	Percent Used (Weighted-Average)
Warranty obligations for microinverters sold since January 1, 2014	Discounted cash flows	Profit element and risk premium	17%
	Discounted cash flows	Credit-adjusted risk-free rate	19%

Sensitivity of Level 3 Inputs

Warranty Obligations

Each of the significant unobservable inputs is independent of the other. The profit element and risk premium are estimated based on requirements of a third-party participant willing to assume the Company’s warranty obligations. The credit-adjusted risk-free rate is determined by reference to the Company’s own credit standing at the fair value measurement date. Increasing (decreasing) the profit element and risk premium input by 100 basis points would not have a material impact on the fair value measurement of the liability. Increasing (decreasing) the discount rate by 100 basis points would result in a ($443,000) $485,000 (decrease) increase, respectively, to the fair value measurement of the liability.

RESTRUCTURING AND OTHER

12 Months Ended

Dec. 31, 2017

Restructuring and Related Activities [Abstract]

RESTRUCTURING AND OTHER

In the third quarter of 2016, the Company began implementing restructuring actions to lower its operating expenses and cost of revenues. The restructuring actions have included reductions in the Company’s global workforce, the elimination of certain non-core projects, consolidation of office space at the Company’s corporate headquarters and the engagement of management consultants to assist the Company in making organizational and structural changes to improve operational efficiencies and reduce expenses.

The following table presents the details of the Company’s restructuring charges for the periods indicated (in thousands):



	Years Ended December 31,
	2017		2016			2015
Employee severance and benefit arrangements	$	2,827	$	1,263		$	—
Asset impairments	522		2,575			—
Consultants engaged in restructuring activities	12,100		—			—
Lease loss and other	1,468		579			—
Gain on business divestiture	—		(640		)	—
Total restructuring and other	$	16,917	$	3,777		$	—

The following table provides information regarding changes in the Company’s accrued restructuring balance for the periods indicated (in thousands):



	Employee Severance and Benefits			Asset Impairments			Lease Loss Reserves and Contractual Obligations			Total
Balance as of December 31, 2015	$	—		$	—		$	—		$	—
Charges	1,263			2,575			579			4,417
Cash payments	(1,065		)	—			(95		)	(1,160		)
Non-cash settlement	—			(2,575		)	—			(2,575		)
Balance as of December 31, 2016	$	198		$	—		$	484		$	682
Charges	2,827			522			13,568			16,917
Cash payments	(2,796		)	—			(12,958		)	(15,754		)
Non-cash settlement	—			(522		)	—			(522		)
Balance at end of period as of December 31, 2017	$	229		$	—		$	1,094		$	1,323

The following table provides information regarding the computation of the Company’s gain on business divestiture included in restructuring and other (in thousands) for the year ended December 31, 2016:



	Business Divestiture
Consideration	$	1,375
Identifiable assets	(979		)
Contingent Consideration	244
Gain on business divestiture	$	640

DEBT

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

DEBT

Term Loan

In July 2016, the Company entered into a Term Loan Agreement (the “Original Term Loan”) with lenders that are affiliates of Tennenbaum Capital Partners, LLC. (the “Lenders”). Under the agreement, the Lenders committed to advance a term loan in an aggregate principal amount of up to $25.0 million with a maturity date of July 1, 2020. The Company borrowed the entire $25.0 million of term loan commitments on the loan closing date. Monthly payments due through June 30, 2017 were interest only, followed by consecutive equal monthly payments of principal plus accrued interest that were to begin on July 1, 2017 and continue through the maturity date. The term loan provided for an interest rate per annum equal to the higher of (i) 10.25% or (ii) LIBOR plus 9.5625%, subject to a 1.0% reduction if the Company achieves minimum levels of Revenue and EBITDA (each as defined in the Term Loan Agreement) for the twelve-consecutive month period ending June 30, 2017 as set forth in the Term Loan Agreement. In addition, the Company paid a commitment fee of 3.3% of the loan amount upon closing and a closing fee of 10.0% of the loan amount is payable in four equal installments at each anniversary of the closing date. The Company could elect to prepay the loan by incurring a prepayment fee between 1% and 3% of the principal amount of the term loan depending on the timing and circumstances of prepayment.

In February 2017, the Company entered into an Amended and Restated Loan and Security Agreement (the “Loan Agreement”) that amended and restated the Original Term Loan. The Loan Agreement provides for a $25.0 million secured term loan to the Company (the “New Term Loan”), which is in addition to the $25.0 million secured term loan borrowed by the Company under the Original Term Loan (together with the “New Term Loan” the “Term Loans”). The New Term Loan has the same July 1, 2020 maturity date that was applicable to the Original Term Loan. The New Term Loan was fully drawn at closing, with approximately $10.3 million of the proceeds used to repay existing combined principal and interest due under the Company’s Revolver with Wells Fargo. Upon the repayment of loans under the Wells Fargo Revolver, the Wells Fargo Revolving Credit Agreement was terminated. The Company expects to use the remainder of the proceeds from the New Term Loan for general corporate purposes.

Monthly payments under the Term Loans through February 28, 2018 are interest only, followed by consecutive equal monthly payments of principal plus accrued interest beginning on March 1, 2018 and continuing through the maturity date. Interest on the Term Loans is the greater of (a) 10.3125%, and (b) a fluctuating rate of interest per annum equal to the three-month LIBOR Rate (rounded up to the nearest 1/16th of one percent) plus 9.25%. In addition, the Company paid a commitment fee of 3.0% of the New Term Loan amount upon closing and a closing fee of 4.0% of the New Term Loan amount, which is payable with the closing fee under the Original Term Loan in four equal installments at each anniversary of the closing date of the Original Loan Agreement. The Company may elect to prepay the Term Loans by incurring a prepayment fee between 1% and 3% of the principal amount of the Term Loans depending on the timing and circumstances of prepayment.

On February 28, 2018, the Company entered into a Second Amendment to the Term Loans. The Amendment decreases by 50% the amount of principal repayments required under the Loan Agreement for the period from March 1, 2018 through December 31, 2018 and provides that the Company shall not prepay any part of the Term Loan during that same period without the Collateral Agent’s prior written consent.

The Term Loans are secured by a first-priority security interest on substantially all assets of the Company; provided, however that the security interest in the Company’s intellectual property may be released if the Company satisfies certain requirements. The Company’s obligations under the Term Loans are not guaranteed by any of the Company’s existing subsidiaries, nor have any existing subsidiaries of the Company pledged any of their assets to secure the Term Loans.

The Loan Agreement requires that (i) at all times from the closing date to and including March 31, 2018, the Company, and any future guarantors, have Unrestricted Cash (as defined in the Loan Agreement) of at least $10.0 million; (ii) at all times from the closing date to and including March 31, 2018, that the aggregate amount of Consolidated Unrestricted Cash, plus the value of Consolidated Receivables, plus the value of Consolidated Inventory (each as defined in the Loan Agreement) divided by the outstanding principal amount of Term Loans, shall equal or exceed 1.5; and (iii) at all times from April 1, 2018 and thereafter, that the aggregate amount of Consolidated Unrestricted Cash, plus the value of Consolidated Receivables, plus the value of Consolidated Inventory divided by the outstanding principal amount of Term Loans, shall equal or exceed 1.75. In addition, the Loan Agreement is subject to customary affirmative and negative covenants including restrictions on creation of liens, dispositions of assets, mergers, changing the nature of its business and dividends and other distributions, in each case subject to certain exceptions. The Term Loan Agreement also contains certain customary events of default including, but not limited to, failure to pay interest, principal and fees or other amounts when due, material breach of any representation or warranty, covenant defaults, cross defaults to other material indebtedness, events of bankruptcy and the occurrence of a material adverse change (as defined in the agreement) to the Company’s business. The Term Loan Agreement offers TCP typical rights and remedies in any event of default, including the ability to declare all amounts outstanding immediately due and payable. The Company was in compliance with all financial covenants as of December 31, 2017.

In connection with the New Term Loan, the Company issued to the Lenders warrants to purchase an aggregate 1,220,000 shares of the Company’s Common Stock at an exercise price of $1.05 per share. The warrants have a term of seven years and contain a “cashless exercise” feature that allows the holder to exercise the warrant without a cash payment upon the terms set forth therein.

The Company estimated the fair value of the warrants by using the Black-Scholes approach and the following assumptions: stock price of $1.56; strike price of $1.05; volatility of 85.9%, risk-free rate of 2.23%; dividend yield of 0%; and a 7 year term. The resulting fair value was used to allocate the proceeds from the Term Loan between liability and equity components.

The Company classified the warrants as equity and allocated the proceeds from the Term Loan and warrants using the relative fair value method. Using this method, the Company allocated $1.4 million to the warrants, which was recorded as equity. This amount represents debt discount that will be amortized to interest expense over the term of the loan.

As of December 31, 2017, the estimated schedule of principal payments due on the term loan (without regard to the February 28, 2018 amendment described above) is as follows (in thousands):



Year	Amounts
2018	$	15,715
2019	20,939
2020	13,346
Total	$	50,000

The amount of estimated schedule of principal payments due on the term loan including the impact of the February 28, 2018 amendment described above is as follows (in thousands):



Year	Amounts
2018	$	8,521
2019	25,333
2020	16,146
Total	$	50,000

Sale of Long Term Financing Receivables

The Company entered into an agreement with a third party in the fourth quarter of 2017 to sell certain current and future receivables at a discount. In December 2017, the third party made an initial purchase of receivables resulting in net proceeds to the Company of $2.8 million. This transaction was recorded as debt on the accompanying consolidated balance sheets, and the debt balance will be relieved by January 2019 as the underlying receivables are settled. The buyer has the option to purchase certain additional future receivables at various fixed discounts. This option was valued at $0.7 million and was recorded as a liability with a corresponding offset to debt as of December 31, 2017. See Note 8, “Fair Value Measurements” for additional information.

Total long-term debt was comprised of the following at December 31, 2017 and 2016 (in thousands):



	December 31, 2017			December 31, 2016
Term loan	$	50,000		$	25,000
Less unamortized discount and issuance costs	(2,111		)	(1,200		)
Carrying amount of term loan	47,889			23,800
Sale of long term financing receivable recorded as debt	2,562			—
Less value of future purchase option	(700		)	—
Carrying amount of sale of long term financing receivable recorded as debt	1,862			—
Total carrying amount of debt	49,751			23,800
Less current portion term loan	(15,715		)	(3,032		)
Less current portion of long term financing receivable recorded as debt	(1,714		)	—
Long-term debt	$	32,322		$	20,768

Revolving Credit Facility

The Company had a $50.0 million revolving credit facility with Wells Fargo Bank, N.A. (“Wells Fargo”) that was entered into in November 2012, as first amended on February 14, 2014. On December 18, 2015, the Company entered into an amended and restated revolving credit agreement with Wells Fargo (the “Revolver”) which extended the maturity date to November 7, 2019 and added an uncommitted accordion feature that could increase the size of the facility by $25.0 million, subject to the satisfaction of certain conditions. The Revolver had a balance of $10.1 million as of December 31, 2016 and was fully repaid and terminated in February 2017.

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

COMMITMENTS AND CONTINGENCIES

Operating Leases—The Company leases office facilities under noncancelable operating leases that expire on various dates through 2022. The terms of the lease agreements generally provide for rental payments on a graduated basis, and certain leases require the Company to pay its portion of executory costs such as taxes, insurance, and operating expenses. The Company recognizes rent expense on a straight-line basis over the lease term.

Rent expense for 2017, 2016 and 2015 was $2.8 million, $3.8 million and $3.2 million, respectively.

The Company’s minimum lease payments under noncancelable operating leases, exclusive of executory costs, as of December 31, 2017 are as follows (in thousands):



2018	$	3,011
2019	3,065
2020	2,919
2021	2,678
2022	1,973
Thereafter	1,544
Total minimum lease payments	$	15,190

Purchase Obligations—The Company has contractual obligations related to component inventory that its primary contract manufacturer procures on its behalf in accordance with its production forecast as well as other inventory related purchase commitments. As of December 31, 2017, these purchase obligations totaled approximately $26.9 million.

Contingencies — From time to time, the Company may be involved in litigation relating to claims arising out of its operations. The Company is not currently involved in any material legal proceedings. The Company may, however, be involved in material legal proceedings in the future. Such matters are subject to uncertainty and there can be no assurance that such legal proceedings will not have a material adverse effect on its business, results of operations, financial position or cash flows.

SALE OF COMMON STOCK	12 Months Ended
SALE OF COMMON STOCK	Dec. 31, 2017
Equity [Abstract]
SALE OF COMMON STOCK	SALE OF COMMON STOCK In January 2017, the Company completed a private placement of securities that resulted in the issuance of approximately 10.8 million shares of common stock and gross proceeds of $10.0 million. In December 2016, the Company entered into an At Market Issuance Sales Agreement (ATM) under which it could sell shares of its common stock up to a gross aggregate offering price of $17.0 million. During the three months ended March 31, 2017 the Company sold approximately 11.1 million shares of common stock under the ATM and received net proceeds of approximately $16.6 million.

STOCK-BASED COMPENSATION

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

STOCK-BASED COMPENSATION

Description of Equity Incentive Plans

2006 Plan

Under the Company’s 2006 Equity Incentive Plan (the “2006 Plan”), equity awards granted generally vest over a four-year period from the date of grant with a contractual term of up to 10 years. As of December 31, 2017, there were 2.3 million shares of options outstanding under the 2006 Plan. No further stock options or other stock awards may be granted under the 2006 Plan.

2011 Plan

Under the 2011 Equity Incentive Plan (the “2011 Plan”), the Company could initially issue up to 2,643,171 shares of its common stock pursuant to stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance-based stock awards, and other forms of equity compensation, or collectively, stock awards, all of which may be granted to employees, including officers, and to non-employee directors and consultants. Options granted under the 2011 Plan before August 1, 2012 generally expire 10 years after the grant date and options granted thereafter generally expire 7 years after the grant date. Equity awards granted under the 2011 Plan generally vest over a four-year period from the date of grant based on continued employment. The number of shares of the Company’s common stock authorized for issuance under the 2011 Plan automatically increases on each January 1 by 4.5% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, or such lesser number of shares of common stock as determined by the board of directors. As of December 31, 2017, 743,329 shares remained available for issuance pursuant to future grants under the 2011 Plan. On January 1, 2018, the shares available for issuance under the 2011 Plan automatically increased by 3,866,120 shares.

2011 Employee Stock Purchase Plan

The 2011 Employee Stock Purchase Plan (“ESPP”) became effective immediately upon the execution and delivery of the underwriting agreement for the Company’s IPO on March 29, 2012. The ESPP authorized the issuance of 669,603 shares of the Company’s common stock pursuant to purchase rights granted to employees. The number of shares of common stock reserved for issuance will automatically increase, on each January 1, by a lesser of (i) 330,396 shares of the Company’s common stock or or (ii) 1.0% of the total number of shares of the Company’s common stock outstanding on December 31 of the preceding calendar year, as determined by the Company’s board of directors.

The ESPP is implemented by concurrent offering periods and each offering period may contain up to four interim purchase periods. In general, offering periods consists of the 24 months periods commencing on each May 15 and November 15 of a calendar year.

Generally, all full time employees, including executive officers, are eligible to participate in the ESPP. The ESPP permits eligible employees to purchase the Company’s common stock through payroll deductions, which may not exceed 15% of the employee’s total compensation subject to certain limits. Stock may be purchased under the plan at a price equal to 85% of the fair market value of the Company’s stock on either the date of purchase or the first day of an offering period, whichever is lower. A two year look-back feature in the Company’s ESPP causes an offering period to reset if the fair value of the Company’s common stock on a purchase date is less than that on the initial offering date for that offering period. The reset feature, when triggered, will be accounted for as a modification to the original offering, resulting in additional expense to be recognized over the 24-month period of the new offering. During any calendar year, participants may not purchase shares of common stock having a value greater than $25,000, based on the fair market value per share of the common stock at the beginning of an offering period.

As of December 31, 2017, there were 290,658 shares remained available for future issuance under the 2011 ESPP. On January 1, 2018, the shares available for issuance under the 2011 ESPP automatically increased by 700,000 shares. At the Annual Meeting of Stockholders held on May 18, 2017 the Company’s stockholders approved an amendment to the Company’s ESPP to increase the aggregate number of shares available for purchase by 400,000 shares and to increase the annual automatic increase in shares reserved for issuance from 330,396 to 700,000 effective January 1, 2018.

Valuation of Equity Awards

Stock Options

The fair value of each option granted was estimated on the date of grant using the Black-Scholes option-pricing model with the following assumptions:

•

Expected term—The expected term of the option awards represents the period of time between the grant date of the option awards and the date the option awards are either exercised, converted or canceled, including an estimate for those option awards still outstanding. The Company used the simplified method, as permitted by the SEC for companies with a limited history of stock option exercise activity, to determine the expected term for its option grants.


•	Expected volatility—The expected volatility was calculated based on the Company’s historical stock prices, supplemented as necessary with historical volatility of the common stock of several peer companies with characteristics similar to those of the Company.


•	Risk-free interest rate—The risk-free interest rate was based on the U.S. Treasury yield curve in effect at the time of grant and with a maturity that approximated the Company’s expected term.


•	Dividend yield—The dividend yield was based on the Company’s dividend history and the anticipated dividend payout over its expected term.

A summary of the weighted-average assumptions used to estimate the fair values of the stock options granted during the periods presented is as follows:



	Years Ended December 31,
	2017			2016			2015
Expected term (in years)	4.4			4.5			4.5
Expected volatility	83.9		%	80.0		%	72.5		%
Annual risk-free rate of return	1.8		%	1.1		%	1.4		%
Dividend yield	—		%	—		%	—		%
Weighted-average fair value on grant date	$	0.76		$	1.29		$	4.68

Restricted Stock Units

The fair value of restricted stock units granted is determined based on the price of the Company’s common stock on the date of grant.

Stock-Based Compensation Expense

The Compensation cost for all stock-based awards expected to vest is measured at fair value on the date of grant and recognized ratably over the requisite service period. The following table summarizes the components of total stock-based compensation expense included in the consolidated statements of operations for the periods presented (in thousands):



	Years Ended December 31,
	2017		2016		2015
Cost of revenues	$	1,072	$	1,188	$	1,217
Research and development	2,573		3,879		4,559
Sales and marketing	1,157		2,144		3,162
General and administrative	1,925		3,115		3,758
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

A summary of stock-based compensation expense associated with each type of award for the periods presented is as follows (in thousands):



	Years Ended December 31,
	2017		2016		2015
Stock options and restricted stock units	$	5,559	$	8,384	$	10,685
ESPP	1,168		1,942		2,011
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

As of December 31, 2017, there was approximately $10.4 million of total unrecognized compensation cost related to unvested equity awards, net of expected forfeitures, which is expected to be recognized over a weighted-average period of 3.0 years.

No income tax benefit has been recognized relating to stock-based compensation expense and no tax benefits have been realized from exercised stock options.

Equity Awards Activity

Stock Options

A summary of the Company’s stock option activity for the periods presented is as follows (in thousands, except per share data):



	Shares		Weighted- Average Exercise Price per Share
Options outstanding — December 31, 2014	8,632		$	4.75
Granted	1,289		8.20
Exercised	(1,079	)	1.40
Canceled	(672	)	9.31
Options outstanding — December 31, 2015	8,170		5.36
Granted	2,440		2.12
Exercised	(375	)	0.39
Canceled	(1,505	)	6.01
Options outstanding — December 31, 2016	8,730		4.55
Granted	4,500		1.22
Exercised	(425	)	0.51
Canceled	(4,379	)	6.91
Options outstanding — December 31, 2017	8,426		1.77

The following table summarizes information about stock options outstanding at December 31, 2017:



	Options Outstanding				Options Exercisable
Range of Exercise Prices	Number of Shares (in thousands)	Weighted- Average Remaining Life (in years)	Weighted- Average Exercise Price		Number of Shares (in thousands)	Weighted- Average Exercise Price
$0.27 —– $0.79	1,690	4.0	$	0.51	1,117	$	0.38
$0.83 —– $1.29	1,565	6.8	1.17		34	1.06
$1.31 —– $1.31	1,751	6.3	1.31		500	1.31
$1.37 —– $1.98	1,726	2.8	1.67		1,415	1.66
$2.00 —– $12.57	1,694	3.8	4.14		1,245	4.62
Total	8,426				4,311

The intrinsic value of options exercised in 2017, 2016 and 2015 was $0.5 million, $0.7 million and $4.9 million, respectively. As of December 31, 2017, there were 8.4 million options outstanding that were vested and expected to vest. Such options have a weighted-average exercise price of $1.77 and a weighted-average remaining contractual term of 4.7 years. As of December 31, 2017, the aggregate intrinsic value was $4.0 million for the 4.3 million exercisable shares. The intrinsic value is based on the Company’s common stock fair value of $2.41 per share as of December 31, 2017.

Restricted Stock Units

A summary of restricted stock unit activity for the periods presented is as follows: (in thousands, except per share data):



	Restricted Stock Units		Weighted Average Fair Value per Share at Grant Date
Outstanding at December 31, 2014	1,345		$	8.25
Granted	683		11.22
Vested	(488	)	8.58
Canceled	(227	)	10.32
Outstanding at December 31, 2015	1,313		9.31
Granted	54		1.99
Vested	(464	)	9.06
Canceled	(297	)	8.32
Outstanding at December 31, 2016	606		9.33
Granted	5,418		1.46
Vested	(885	)	3.81
Canceled	(1,634	)	1.90
Outstanding at December 31, 2017	3,505		2.03

The intrinsic value of restricted stock units vested during 2017, 2016 and 2015 was $0.9 million, $0.9 million and $4.2 million, respectively. As of December 31, 2017, the restricted stock units outstanding had a weighted average remaining contractual term of 3.1 years with an intrinsic value of $8.4 million.

On April 3, 2017, the Company commenced a Tender Offer (Offer) to exchange out of the money stock options for restricted stock units. The Offer expired on Monday, May 1, 2017. Pursuant to the Offer, the Company accepted elections to exchange options to purchase 2,362,470 shares of common stock and issued replacement awards of restricted stock units for 733,559 shares of common stock. As the transaction approximated a value-for-value exchange, it did not have a material impact on the Company’s stock based compensation expense.

ESPP

A summary of ESPP activity for the years presented is as follows: (in thousands, except per share data):



	Years Ended December 31,
	2017		2016		2015
Proceeds from common stock issued under ESPP	$	313	$	999	$	2,497
Shares of common stock issued	478		659		499
Weighted-average price per share	$	0.65	$	1.52	$	5.00

INCOME TAXES

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

INCOME TAXES

The domestic and foreign components of loss before provision for income taxes consisted of the following (in thousands):



	Years Ended December 31,
	2017			2016			2015
United States	$	(47,882	)	$	(67,631	)	$	(22,120	)
Foreign	2,541			1,644			1,417
Total	$	(45,341	)	$	(65,987	)	$	(20,703	)

The (benefit) provision for income taxes for the years presented is as follows (in thousands):



	Years Ended December 31,
	2017			2016		2015
Current:
Federal	$	—		$	—	$	—
State	21			36		44
Foreign	1,224			785		693
	1,245			821		737
Deferred:
Federal	(1,092		)	594		652
State	(21		)	59		41
Foreign	(281		)	1		(51		)
	(1,394		)	654		642
(Benefit) provision for income taxes	$	(149	)	$	1,475	$	1,379

A reconciliation of the provision for income taxes and the amount computed by applying the statutory federal income tax rate of 34% to loss before income taxes for the years presented is as follows (in thousands):



	Years Ended December 31,
	2017			2016			2015
Income tax benefit at statutory federal rate	$	(15,416	)	$	(22,435	)	$	(7,039	)
State taxes, net of federal benefit	(64		)	63			56
Change in valuation allowance	(20,571		)	21,370			7,812
Foreign tax rate and tax law differential	(133		)	27			(29		)
Tax credits	(382		)	(1,179		)	(1,553		)
Stock-based compensation	761			1,775			1,932
Other permanent items	479			776			61
Other nondeductible/nontaxable items	930			920			(72		)
Uncertain tax positions	106			158			211
Tax law changes	34,141			—			—
(Benefit) provision for income taxes	$	(149	)	$	1,475		$	1,379

A summary of significant components of the Company’s deferred tax assets and liabilities as of December 31, 2017 and 2016 is as follows (in thousands):



	December 31,
	2017			2016
Deferred tax assets:
Allowances and reserves	$	9,748		$	16,032
Net operating loss and tax credit carryforwards	66,243			67,875
Stock-based compensation	2,528			3,033
Deferred revenue	7,210			8,289
Fixed assets and intangibles	4,369			7,661
Other	278			2,857
Subtotal	90,376			105,747
Less valuation allowance	(88,789		)	(104,554		)
Total deferred tax assets, net of valuation allowance	1,587			1,193
Deferred tax liabilities:
Goodwill	(992		)	(1,346		)
Unremitted foreign earnings	(10		)	(748		)
Total deferred tax liabilities	(1,002		)	(2,094		)
Net deferred tax asset/(liability)	$	585		$	(901	)

Accounting for income taxes requires that companies assess whether valuation allowances should be established against their deferred tax assets based on consideration of all available evidence, both positive and negative, using a “more likely than not” standard. This assessment considers, among other matters, the nature, frequency and amount of recent losses, the duration of statutory carryforward periods, and tax planning strategies. In making such judgments, significant weight is given to evidence that can be objectively verified. Due to the history of losses the Company has generated in the United States since inception, the Company believes that it is more-likely-than-not that all of its U.S. and state deferred tax assets will not be realized as of December 31, 2017. Therefore, the Company has recorded a full valuation allowance on its U.S. and state deferred tax assets at December 31, 2017 of $88.8 million, which is a decrease of $15.8 million as compared to December 31, 2016. Should the Company determine that it would be able to realize its deferred tax assets in the foreseeable future, an adjustment to the deferred tax assets may cause a material increase to income in the period such determination is made. Significant management judgment is required in determining the period in which the reversal of a valuation allowance should occur.

On December 22, 2017, H.R. 1 (the "Act") was enacted and included broad tax reforms. The Act reduced the U.S. corporate tax rate from 35% to 21% effective January 1, 2018. The rate change resulted in a $28.3 million reduction in the Company's deferred tax assets from prior year. Tax law changes created the ability for federal indefinite lived assets to be generated in the years following 2017. As such, an income tax benefit was recorded to reduce the domestic indefinite lived liability that is now partially offset by indefinite lived deferred tax assets. The Company has elected to treat taxes on Global Intangible Low Tax Income ("GILTI") as period costs. The Act also imposed a deemed repatriation of foreign earnings previously considered deferred for US tax purposes. The Company had previously recorded a deferred tax liability for such unremitted earnings that were not considered permanently reinvested in the foreign jurisdictions. As of December 31, 2017, the Company has recognized the previously deferred federal liability in accordance with the Act. The Company continues to include deferred tax liabilities for potential future tax consequences of remitting such earnings, such as foreign withholding and state taxes, as of December 31, 2017.

The Company has net operating loss carryforwards for federal and California income tax purposes of approximately $176.2 million and $89.1 million, respectively, as of December 31, 2017. The federal and state net operating loss carryforwards, if not utilized, will expire beginning in 2028.

The Company has approximately $11.3 million of federal research credit and $11.7 million of state research credit carryforwards. The federal credits begin to expire in 2026 and the state credits can be carried forward indefinitely.

Utilization of some of the federal and state net operating loss and credit carryforwards are subject to annual limitations due to the “change in ownership” provisions of the Internal Revenue Code of 1986 and similar state provisions. Company does not anticipate these limitations, if any, will significantly impact its ability to utilize the net operating losses and tax credit carryforwards.

The accounting for uncertain tax positions prescribes a recognition threshold and measurement attribute for the financial statement recognition and measurement of a tax position taken or expected to be taken in a tax return. The Company is required to recognize in the financial statements the impact of a tax position, if that position is more-likely-than-not of being sustained on audit, based on the technical merits of the position. The Company recorded a net charge for unrecognized tax benefits in 2017 of $0.1 million.

The Company does not have any tax positions for which it is reasonably possible the total amount of gross unrecognized tax benefits will increase or decrease over the next year. The unrecognized tax benefits may increase or change during the next year for items that arise in the ordinary course of business. The Company recognizes interest and penalties related to uncertain tax positions in income tax expense.

A tabular reconciliation of the total amounts of unrecognized tax benefits for the years presented is as follows (in thousands):



	Year Ended December 31,
	2017			2016			2015
Unrecognized tax benefits—at beginning of year	$	6,016		$	5,482		$	4,426
Increases in balances related to tax positions taken in prior years	—			—			14
Decreases in balances related to tax positions taken in prior years	(135		)	—			—
Increases in balances related to tax positions taken in current year	306			571			1,053
Lapses in statutes of limitations	(81		)	(37		)	(11		)
Unrecognized tax benefits—at end of year	$	6,106		$	6,016		$	5,482

The Company’s tax returns continue to remain subject to examination by U.S. federal authorities for the years 2006 through 2017 and by California state authorities for the years 2006 through 2017 due to the use of net operating losses and credits.

CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS	12 Months Ended
CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS	Dec. 31, 2017
Risks and Uncertainties [Abstract]
CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS	CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS The Company is potentially subject to financial instrument concentration of credit risk through its cash and cash equivalents and accounts receivable. The Company places its cash and cash equivalents with high quality institutions and performs periodic evaluations of their relative credit standing. Accounts receivable can be potentially exposed to a concentration of credit risk with its major customers. As of December 31, 2017, amounts due from one customer represented approximately 22% of the total accounts receivable balance. As of December 31, 2016, amounts due from one customer represented 25% of the total accounts receivable balance. In 2017, two customers accounted for approximately 15% and 11% of total net revenues. In 2016, one customer accounted for approximately 18% of total net revenues. In 2015, two customers accounted for approximately 17% and 12% of total net revenues.

NET LOSS PER SHARE

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

NET LOSS PER SHARE

Basic net loss per share is calculated by dividing net loss by the weighted average number of shares outstanding for the period. Diluted net loss per share is calculated by dividing net loss by the weighted average number of common shares and potential dilutive common share equivalents outstanding during the period if the effect is dilutive. The Company’s potentially dilutive common shares include outstanding stock options and warrants and non-vested restricted stock units.

The following table presents the potential common shares outstanding that were excluded from the computation of diluted net loss per share attributable to common stockholders for the periods presented because including them would have been anti-dilutive (in thousands):



	Years Ended December 31,
	2017	2016	2015
Stock options to purchase common stock	8,433	8,981	8,646
Unvested restricted stock units	3,029	906	1,506
Warrants to purchase common stock	1,083	—	111
Total	12,545	9,887	10,263

SEGMENT AND GEOGRAPHIC INFORMATION

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

SEGMENT AND GEOGRAPHIC INFORMATION

The Company’s chief operating decision maker is the Chief Executive Officer. The Chief Executive Officer reviews financial information presented on a consolidated basis. The Company has one business activity, which entails the design, development, manufacture and sale of microinverter systems for the solar photovoltaic industry. There are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level. Accordingly, management has determined that the Company has a single operating and reportable segment.

The following tables present net revenues (based on the destination of shipments) and long-lived assets by geographic region as of and for the periods presented (in thousands):

Net Revenues



	Years Ended December 31,
	2017		2016		2015
United States	$	199,565	$	259,080	$	303,195
International	86,601		63,511		54,054
Total	$	286,166	$	322,591	$	357,249

Long-Lived Assets



	As of December 31,
	2017		2016		2015
United States	$	16,899	$	22,634	$	21,913
China	7,164		5,727		7,950
Other	2,420		3,079		2,255
Total	$	26,483	$	31,440	$	32,118

QUARTERLY FINANCIAL INFORMATION (UNAUDITED)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

QUARTERLY FINANCIAL INFORMATION (UNAUDITED)

The following tables show a summary of the Company’s quarterly financial information for each of the four quarters of 2017 and 2016 (in thousands, except per share data):



	Year Ended December 31, 2017
	March 31			June 30			September 30			December 31

Net revenues	$	54,751		$	74,704		$	77,038		$	79,674
Cost of revenues	47,703			61,157			60,577			60,685
Gross profit	7,048			13,547			16,461			18,989
Operating expenses:
Research and development	9,605			7,947			7,397			8,208
Sales and marketing	6,458			6,274			5,453			4,940
General and administrative	5,833			4,964			5,441			5,983
Restructuring charges	7,247			3,609			4,071			1,991
Total operating expenses	29,143			22,794			22,362			21,122
Loss from operations	(22,095		)	(9,247		)	(5,901		)	(2,133		)
Other income expense, net	(1,079		)	(1,992		)	(1,137		)	(1,755		)
Loss before income taxes	(23,174		)	(11,239		)	(7,038		)	(3,888		)
Income tax benefit (provision)	(131		)	(854		)	184			948
Net loss	$	(23,305	)	$	(12,093	)	$	(6,854	)	$	(2,940	)
Net loss per share, basic and diluted	$	(0.30	)	$	(0.14	)	$	(0.08	)	$	(0.03	)

	Year Ended December 31, 2016
	March 31			June 30			September 30			December 31
Net revenues	$	64,121		$	79,185		$	88,684		$	90,601
Cost of revenues	52,361			65,049			72,805			74,367
Gross profit	11,760			14,136			15,879			16,234
Operating expenses:
Research and development	13,066			13,091			13,169			11,378
Sales and marketing	10,215			9,987			11,016			7,592
General and administrative	7,567			6,846			6,708			6,296
Restructuring charges	—			—			2,717			1,060
Total operating expenses	30,848			29,924			33,610			26,326
Loss from operations	(19,088		)	(15,788		)	(17,731		)	(10,092		)
Other income expense, net	529			(591		)	(881		)	(2,345		)
Loss before income taxes	(18,559		)	(16,379		)	(18,612		)	(12,437		)
Income tax provision	(236		)	(344		)	(144		)	(751		)
Net loss	$	(18,795	)	$	(16,723	)	$	(18,756	)	$	(13,188	)
Net loss per share, basic and diluted	$	(0.41	)	$	(0.36	)	$	(0.40	)	$	(0.21	)

SUBSEQUENT EVENTS	12 Months Ended
SUBSEQUENT EVENTS	Dec. 31, 2017
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS On February 4, 2018, the Company entered into a securities purchase agreement with an investor pursuant to which the Company, in a private placement, agreed to issue and sell to the investor 9,523,809 shares of the Company’s common stock, at a price per share of $2.10, for gross proceeds of $20.0 million. The Company intends to use the net proceeds from the Private Placement for general corporate purposes. On February 28, 2018, the Company entered into a Second Amendment to the Term Loans. The Amendment decreases by 50% the amount of principal repayments required under the Loan Agreement for the period from March 1, 2018 through December 31, 2018 and provides that the Company shall not prepay any part of the Term Loan during that same period without the Collateral Agent’s prior written consent.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (“US GAAP”). The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. The Company has taken and continues to take actions to improve its financial stability. Such actions include accessing additional capital, reducing its operating expense structure and substantially transitioning to its next generation of microinverters, which offer increased functionality and have a reduced cost profile.
Use of Estimates	Use of Estimates The preparation of the Company’s consolidated financial statements in conformity with US GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of income and expenses during the reporting period. These estimates are based on information available as of the date of the financial statements; therefore, actual results could differ materially from management’s estimates using different assumptions or under different conditions.
Revenue Recognition	Revenue Recognition The Company generates revenue from sales of its microinverter systems, which include microinverter units and related accessories, an Envoy communications gateway, the cloud-based Enlighten monitoring service, and AC Battery storage solutions to distributors, large installers, OEMs and strategic partners. Enlighten service revenue represented less than 2% of the total revenues for all periods presented. Revenue from sales of the Company’s products is recognized when: (i) persuasive evidence of an arrangement exists; (ii) delivery of the products has occurred in accordance with the terms of the sales agreement and title and risk of loss have passed to the customer; (iii) the sale price is fixed or determinable; and (iv) collection is reasonably assured. Provisions for rebates, sales incentives, and discounts to customers are accounted for as reductions in revenue in the same period the related sales are recorded. Sales of an Envoy communications gateway include the Enlighten cloud-based monitoring service. The allocation of revenue between the two deliverables is based on the Company’s best estimate of selling price determined by considering multiple factors including internal costs, gross margin and historical pricing practices. After allocating the overall consideration from such sale to each deliverable using a best estimate of the selling price, revenue from the sale of Envoy hardware devices is recognized upon shipment, assuming all other revenue recognition criteria have been met. Through September 30, 2017 the estimated economic life of the related Envoy devices was used to determine the period over which revenue from the cloud-based monitoring service was recognized as adequate historical user data was not available. During the fourth quarter of 2017 the Company determined historical user data was available to adequately assess the period over which the service obligation was met. As a result, the Company shortened the estimated service period of the Enlighten from 10 years to 6.5 years effective October 1, 2017. The impact of the change is estimate was an increase to revenue and earnings in the fourth quarter of 2017 of approximately $2.6 million and a reduction of net loss per share of approximately $0.03. Deferred revenues consist of payments received from customers in advance of revenue recognition for the Company’s products and services as described above. As of December 31, 2017 and 2016, deferred revenues consist primarily of Enlighten service revenue.
Cost of Revenues	Cost of Revenues The Company includes the following in cost of revenues: product costs, warranty, manufacturing personnel and logistics costs, freight costs, inventory write-downs, hosting services costs related to the Company’s Enlighten service offering, and depreciation and amortization of manufacturing test equipment.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments, such as certificates of deposit and money market instruments with maturities of three months or less at the time of acquisition to be cash equivalents. For all periods presented, its cash balances consist of amounts held in non-interest-bearing deposits and money market accounts.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of the Company’s cash and cash equivalents, accounts receivable, accounts payable and accrued liabilities approximate fair value because of the short maturity of those instruments.
Allowances for Doubtful Accounts	Allowances for Doubtful Accounts The Company maintains allowances for doubtful accounts for uncollectible accounts receivable. Management estimates anticipated losses from doubtful accounts based on days past due, collection history and the financial health of customers.
Inventory	Inventory Inventory is valued at the lower of cost or market. Market is current replacement cost (by purchase or by reproduction, dependent on the type of inventory). In cases where market exceeds net realizable value (i.e., estimated selling price less reasonably predictable costs of completion and disposal), inventories are stated at net realizable value. Market is not considered to be less than net realizable value reduced by an allowance for an approximately normal profit margin. The Company determines cost on a first-in first-out basis. Management assesses the valuation on a quarterly basis and writes down the value for any excess and obsolete inventory based upon expected demand, anticipated sales price, effect of new product introductions, product obsolescence, customer concentrations, product merchantability and other factors. Inventory write-downs are equal to the difference between the cost of inventories and market.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation. Cost includes amounts paid to acquire or construct the asset as well as any expenditure that substantially adds to the value of or significantly extends the useful life of an existing asset. Repair and maintenance costs are expensed as incurred. Depreciation and amortization is computed using the straight-line method over the estimated useful lives of the assets, which range from three to ten years. Leasehold improvements are amortized over the shorter of the lease term or expected useful life of the improvements.
Capitalized Software Costs	Capitalized Software Costs Internally used software, whether purchased or developed, is capitalized and amortized on a straight-line basis over its estimated useful life. Costs associated with internally developed software are expensed until the point at which the project has reached the development stage. Subsequent additions, modifications or upgrades to internal-use software are capitalized only to the extent that they provide additional functionality. Software maintenance and training costs are expensed in the period in which they are incurred. The capitalization of software requires judgment in determining when a project has reached the development stage and the period over which the Company expects to benefit from the use of that software.
Long-Lived Assets	Long-Lived Assets Property, plant and equipment, including capitalized software costs, are recorded at cost. Property, plant and equipment amounts are reviewed for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset (asset group) may not be recoverable. An impairment loss would be recognized when the carrying amount of an asset exceeds the estimated undiscounted future cash flows expected to result from the use of the asset and its eventual disposition. The amount of the impairment loss to be recorded is calculated by the excess of the asset's carrying value over its fair value. Fair value is generally determined using a discounted cash flow analysis.
Goodwill and Intangible Assets	Goodwill Goodwill results from the purchase consideration paid in excess of the fair value of the net assets recorded in connection with a business acquisition. Goodwill is not amortized, but is assessed for potential impairment at least annually during the fourth quarter of each fiscal year or between annual tests if an event occurs or circumstances change that would indicate the carrying amount may be impaired. Goodwill is tested at the reporting unit level, which the Company has determined to be the same as the entity as a whole (entity level). Once goodwill has been assigned to a reporting unit, it is no longer associated with a particular acquisition; therefore, all of the activities within a reporting unit, whether acquired or organically grown, are available to support the goodwill value. Based on management’s goodwill impairment tests, there was no impairment of goodwill in any of the years presented. Intangible Assets Intangible assets include patents and other purchased intangible assets. Intangible assets with finite lives are amortized on a straight-line basis, with estimated useful lives ranging from 3 to 5 years. Indefinite-lived intangible assets are tested for impairment annually and are also tested for impairment between annual tests if an event occurs or circumstances change that would indicate that the carrying amount may be impaired. Intangible assets with finite lives are tested for impairment whenever events or circumstances indicate that the carrying amount of an asset (asset group) may not be recoverable. An impairment loss is recognized when the carrying amount of an asset exceeds the estimated undiscounted cash flows used in determining the fair value of the asset. The amount of the impairment loss to be recorded is calculated by the excess of the asset's carrying value over its fair value. Fair value is generally determined using a discounted cash flow analysis. There was no impairment of intangible assets in any of the years presented.
Warranty Obligations	Warranty Obligations Microinverters Sold Through December 31, 2013 The Company’s warranty accrual provides for the replacement of microinverter units that fail during the product’s warranty term (15 years for first and second generation microinverters and up to 25 years for third and fourth generation microinverters). On a quarterly basis, the Company employs a consistent, systematic and rational methodology to assess the adequacy of its warranty liability. This assessment includes updating all key estimates and assumptions for each generation of product, based on historical results, trends and the most current data available as of the filing date. The key estimates and assumptions used in the warranty liability are thoroughly reviewed by management on a quarterly basis. The key estimates used by the Company to estimate its warranty liability are: (1) the number of units expected to fail over time (i.e. failure rate); (2) the number of failed units expected to result in warranty claims over time (i.e. claim rate); and (3) the per unit cost of replacement units, including outbound shipping and limited labor costs, expected to be incurred to replace failed units over time (i.e. replacement cost). Estimated Failure Rates—The Company’s Quality and Reliability department has primary responsibility to determine the estimated failure rates for each generation of microinverter. To establish initial failure rate estimates for each generation of microinverter, the Company’s quality engineers use a combination of industry standard MTBF (Mean Time Between Failure) estimates for individual components contained in its microinverters, third party data collected on similar equipment deployed in outdoor environments similar to those in which the Company’s microinverters are installed, and rigorous long term reliability and accelerated life cycle testing which simulates the service life of the microinverter in a short period of time. As units are deployed into operating environments, the Company continues to monitor product performance via its Enlighten monitoring platform. It typically takes three to nine months between the date of sale and date of end-user installation. Consequently, the Company’s ability to monitor actual failures of units sold similarly lags by three to nine months. When a microinverter fails and is returned, the Company performs diagnostic root cause failure analysis to understand and isolate the underlying mechanism(s) causing the failure. The Company then uses the results of this analysis (combined with the actual, cumulative performance data collected on those units prior to failure via Enlighten) to draw conclusions with respect to how or if the identified failure mechanism(s) will impact the remaining units deployed in the installed base. Estimated Claim Rates—Warranty claim rate estimates are based upon assumptions with respect to expected customer behavior over the warranty period. As the vast majority of the Company’s microinverters have been sold to end users for residential applications, the Company believes that warranty claim rates will be affected by changes over time in residential home ownership because the Company expects that subsequent homeowners are less likely to file claims than the homeowners who originally purchase the microinverters. Estimated Replacement Costs—three factors are considered in the Company’s analysis of estimated replacement cost: (1) the estimated cost of replacement microinverters; (2) the estimated cost to ship replacement microinverters to end users; and (3) the estimated labor reimbursement expected to be paid to third party installers performing replacement services for the end user. Because the Company’s warranty provides for the replacement of defective microinverters over long periods of time (between 15 and 25 years, depending on the generation of product purchased), the estimated per unit cost of current and future product generations is considered in the estimated replacement cost. Estimated costs to ship replacement units are based on observable, market-based shipping costs paid by the Company to third party freight carriers. The Company has a separate program that allows third-party installers to claim fixed-dollar reimbursements for labor costs they incur to replace failed microinverter units for a limited time from the date of original installation. Included in the Company’s estimated replacement cost is an analysis of the number of fixed-dollar labor reimbursements expected to be claimed by third party installers over the limited offering period. In addition to the key estimates noted above, the Company also compares actual warranty results to expected results and evaluates any significant differences. Management may make additional adjustments to the warranty provision based on performance trends or other qualitative factors. If actual failure rates, claim rates, or replacement costs differ from the Company’s estimates in future periods, changes to these estimates may be required, resulting in increases or decreases in the Company’s warranty obligations. Such increases or decreases could be material. Fair Value Option for Microinverters Sold Since January 1, 2014 The Company’s warranty obligations related to microinverters sold since January 1, 2014 provide the Company the right, but not the requirement, to assign its warranty obligations to a third-party. Under Accounting Standards Codification (“ASC”) 825—Financial Instruments, (“fair value option”), an entity may choose to elect the fair value option for such warranties at the time it first recognizes the eligible item. The Company made an irrevocable election to account for all eligible warranty obligations associated with microinverters sold since January 1, 2014 at fair value. This election was made to reflect the underlying economics of the time value of money for an obligation that will be settled over an extended period of up to 25 years. The Company estimates the fair value of warranty obligations by calculating the warranty obligations in the same manner as for sales prior to January 1, 2014 and applying an expected present value technique to that result. The expected present value technique, an income approach, converts future amounts into a single current discounted amount. In addition to the key estimates of failure rates, claim rates and replacement costs, the Company used certain inputs that are unobservable and significant to the overall fair value measurement. Such additional assumptions included compensation comprised of a profit element and risk premium required of a market participant to assume the obligation and a discount rate based on the Company’s credit-adjusted risk-free rate. See Note 8, (“Fair Value Measurements”) for additional information. Warranty obligations initially recorded at fair value at the time of sale will be subsequently re-measured to fair value at each reporting date. In addition, the fair value of the liability will be accreted over the corresponding term of the warranty of up to 25 years using the interest method. Warranty for Other Products The Company offers a 5 year warranty for its Envoy communications gateway and a 10 year warranty on its AC Battery storage solution. The warranties provide the Company with the right, but not the obligation, to assign its warranty obligations to a third-party. As such, warranties for Envoy and AC Battery storage solution products are accounted for under the fair value method of accounting.
Research and Development Costs	Research and Development Costs The Company expenses research and development costs as incurred.
Stock-Based Compensation	Stock-Based Compensation Share-based payments are required to be recognized in the Company’s consolidated statements of operations based on their fair values and the estimated number of shares expected to vest. The Company measures stock-based compensation expense for all share-based payment awards, including stock options made to employees and directors, based on the estimated fair values on the date of the grant. The fair value of stock options granted is estimated using the Black-Scholes option valuation model. The fair value of restricted stock units granted is determined based on the price of the Company’s common stock on the date of grant. Stock-based compensation, net of estimated forfeitures, is recognized on a straight-line basis over the requisite service period, which is typically four years.
Comprehensive Loss	Comprehensive Loss Comprehensive loss consists of two components, net loss and other comprehensive income (loss). Other comprehensive income (loss) refers to gains and losses that are recorded as an element of stockholders’ equity but are excluded from net income. The Company’s other comprehensive income (loss) consists of foreign currency translation adjustments for all periods presented.
Income Taxes	Income Taxes The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected tax consequences of temporary differences between the tax bases of assets and liabilities for financial reporting purposes and amounts recognized for income tax purposes. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized. The Company operates in various tax jurisdictions and is subject to audit by various tax authorities. The Company follows accounting for uncertainty in income taxes which requires that the tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. The Company considers many factors when evaluating and estimating its tax positions and tax benefits, which may require periodic adjustments and which may not accurately anticipate actual outcomes.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements Not Yet Effective	Recently Adopted Accounting Pronouncements In July 2015, the FASB issued ASU 2015-11, “Simplifying the Measurement of Inventory,” which requires most entities to measure most inventories at the lower of cost or net realizable value ("NRV"). This simplifies the evaluation from the current method of lower of cost or market, where market is based on one of three measures (i.e. replacement cost, net realizable value, or net realizable value less a normal profit margin). ASU 2015-11 does not apply to inventories measured under the last-in, first-out method or the retail inventory method, and defines NRV as the “estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation.” This standard, which was adopted in the first quarter of 2017, did not have a material impact on the consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, “Improvements to Employee Share-Based Payment Accounting,” which will simplify the income tax consequences, accounting for forfeitures and classification on the Statements of Consolidated Cash Flows. This standard, which was adopted in the first quarter of 2017, did not have a material impact on the consolidated financial statements. In January 2017, the FASB issued ASU 2017-04, “Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment.” This ASU simplifies the subsequent measurement of goodwill, the FASB eliminated Step 2 from the goodwill impairment test. Under the amendments in this ASU, an entity should perform its annual, or interim, goodwill impairment test by comparing the fair value of a reporting unit with its carrying amount. An entity should recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value; however, the loss recognized should not exceed the total amount of goodwill allocated to that reporting unit. Additionally, an entity should consider income tax effects from any tax deductible goodwill on the carrying amount of the reporting unit when measuring the goodwill impairment loss, if applicable. The FASB also eliminated the requirements for any reporting unit with a zero or negative carrying amount to perform a qualitative assessment and, if it fails that qualitative test, to perform Step 2 of the goodwill impairment test. Therefore, the same impairment assessment applies to all reporting units. An entity is required to disclose the amount of goodwill allocated to each reporting unit with a zero or negative carrying amount of net assets. An entity still has the option to perform the qualitative assessment for a reporting unit to determine if the quantitative impairment test is necessary. A public business entity that is an SEC filer should adopt the amendments in this Update for its annual or any interim goodwill impairment tests in fiscal years beginning after December 15, 2019. Early adoption is permitted for interim or annual goodwill impairment tests performed on testing dates after January 1, 2017. ASU 2017-04 was early adopted by the Company for the year beginning January 1, 2017. The Company has a single reporting unit, and adoption of the standard did not have a material impact on the Company's consolidated financial statements. Recent Accounting Pronouncements Not Yet Effective In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers: Topic 606 and issued subsequent amendments to the initial guidance in August 2015, March 2016, April 2016, May 2016 and December 2016, collectively “Topic 606”). Topic 606 supersedes nearly all existing revenue recognition guidance under GAAP. The standard is effective for and was adopted by the Company on January 1, 2018. The updated standard’s core principle is that revenue is recognized when the customer obtains control of promised goods or services in an amount that reflects the consideration to which an entity expects to be received in exchange for those goods or services. The standard generally requires an entity to identify performance obligations in its contracts, estimate the amount of variable consideration to be received in the transaction price, allocate the transaction price to each separate performance obligation, and recognize revenue as obligations are satisfied. In addition, the updated standard requires additional disclosure about the nature, amount, timing and uncertainty of revenue and cash flows arising from customer contracts. The guidance permits two methods of adoption, the full retrospective method applying the standard to each prior reporting period presented, or the modified retrospective method with a cumulative effect of initially applying the guidance recognized at the date of initial application. The Company will adopt the standard using the modified retrospective method with a cumulative catch up adjustment to accumulated deficit and will provide additional disclosures comparing results to previous GAAP in its 2018 consolidated financial statements. The most significant impacts upon adoption of the standard will be how the Company accounts for revenue related to its envoy communications device and related enlighten service and the timing of when certain sales incentives will be recognized. Under ASC 605 the Company’s monitoring hardware and service are considered two units of accounting with a portion of the consideration related to the hardware recognized upfront and the remaining deferred over the estimated service period. Under ASC 606 the full consideration for these products represents a single performance obligation and is deferred over the estimated service period. This treatment will result in an increase in deferred revenue of approximately $77 million, an increase in deferred costs of approximately $43 million and an increase in accumulated deficit of approximately $34 million upon adoption of ASC 606. Under ASC 605 the Company recorded certain contra revenue promotions at the later of the date revenue was recognized or the date at which the promotional offer was extended. Under ASC 606 all such contra revenue programs will be treated as variable consideration and recognized at the time the related revenue is recorded. This change in timing will result in an increase in accrued liabilities of approximately $6 million and an increase to accumulated deficit in the same amount upon adoption of ASC 606. The change in accounting treatment affects the timing of the recognition of certain contra revenue programs, but the overall income statement impact of this new accounting method is expected to be immaterial. Under ASC 605, the Company expensed commission costs as incurred. The new standard requires upfront contract acquisition costs, such as sales commissions, to be capitalized and amortized over the estimated life of the asset. Under the new guidance, the Company will utilize the practical expedient permitting expensing of costs to obtain a contract when the expected amortization period is one year or less, which typically results in expensing commissions paid. Commissions related to the Company’s sale of monitoring hardware and service will be capitalized and amortized over the period of the associated revenue, which is 6.5 years. This treatment will result in an increase in deferred costs of approximately $0.8 million and an increase in accumulated deficit by the same amount upon adoption of ASC 606. The amortization of these deferred costs is immaterial to the Company’s income statement. The Company does not expect the adoption of ASC 606 to have a material impact on the amount or timing of revenue recognition related to specific customer contracts. In January 2016, the FASB issued ASU 2016-01, “Recognition and Measurement of Financial Assets and Financial Liabilities,” which amends certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. Changes to the current guidance include the accounting for equity investments, the presentation and disclosure requirements for financial instruments, and the assessment of valuation allowance on deferred tax assets related to available-for-sale securities. In addition, ASU 2016-01 establishes an incremental recognition and disclosure requirement related to the presentation of fair value changes of financial liabilities for which the fair value option has been elected. Under this guidance, an entity would be required to separately present in other comprehensive income the portion of the total fair value change attributable to instrument-specific credit risk as opposed to reflecting the entire amount in earnings. ASU 2016-01 is effective for fiscal years and interim periods beginning after December 15, 2017, and upon adoption, an entity should apply the amendments by means of a cumulative-effect adjustment to the balance sheet at the beginning of the first reporting period in which the guidance is effective. Early adoption is not permitted except for the provision to record fair value changes for financial liabilities under the fair value option resulting from instrument-specific credit risk in other comprehensive income. The Company does not expect the adoption of this standard to have a material impact on the consolidated financial statements. In February 2016, the FASB issued Accounting Standards Codification (“ASC”) 842 (“ASC 842”), “Leases” which replaces the existing guidance in ASC 840, Leases. ASC 842 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. ASC 842 requires a dual approach for lessee accounting under which a lessee would account for leases as finance leases or operating leases. Both finance leases and operating leases will result in the lessee recognizing a right-of-use (ROU) asset and a corresponding lease liability. For finance leases the lessee would recognize interest expense and amortization of the ROU asset and for operating leases the lessee would recognize a straight-line total lease expense. The Company is currently evaluating the impact of adoption on the consolidated financial statements. In November 2016, the FASB issued Accounting Standards Update No. 2016-18 (ASU 2016-18), “Statement of Cash Flows,” which requires companies to include amounts generally described as restricted cash and restricted cash equivalents in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company does not expect the adoption of this guidance to have a material impact on the consolidated financial statements. In May 2017, the FASB issued ASU 2017-09 (ASU 2017-09), "Compensation - Stock Compensation." ASU 2017-09 was issued to provide clarity and reduce both 1) diversity in practice and 2) cost and complexity when applying the guidance in Topic 718 to a change in the terms or conditions of a share-based payment award. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting under Topic 718. ASU 2017-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The Company is currently evaluating the impact of adoption on the consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2017

Accounting Policies [Abstract]

Schedule of Activity in Allowance for Doubtful Accounts

The following table sets forth activities in the allowance for doubtful accounts for the periods indicated (in thousands):



	December 31,
	2017			2016			2015
Balance, at beginning of year	$	2,921		$	1,808		$	569
Net charges to expenses	476			3,097			1,502
Write-offs, net of recoveries	(1,019		)	(1,984		)	(263		)
Balance, at end of year	$	2,378		$	2,921		$	1,808

INVENTORY (Tables)

12 Months Ended

Dec. 31, 2017

Inventory Disclosure [Abstract]

Summary of Inventory

Inventory as of December 31, 2017 and 2016, consists of the following (in thousands):



	December 31,
	2017		2016
Raw materials	$	2,341	$	5,095
Finished goods	23,658		26,865
Total inventory	$	25,999	$	31,960

PROPERTY AND EQUIPMENT, NET (Tables)

12 Months Ended

Dec. 31, 2017

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

As of December 31, 2017 and 2016, property and equipment consists of the following (in thousands):



	Estimated Useful Life (Years)	December 31,
	Estimated Useful Life (Years)	2017			2016
Equipment and machinery	7-10	$	41,148		$	38,486
Furniture and fixtures	5–7	2,188			2,635
Computer equipment	3–5	2,627			2,913
Capitalized software costs	3–5	11,749			11,324
Leasehold improvements	4–10	8,537			9,477
Construction in process		4,672			6,275
Total		70,921			71,110
Less accumulated depreciation and amortization		(44,438		)	(39,670		)
Property and equipment, net		$	26,483		$	31,440

GOODWILL AND INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2017

Goodwill and Intangible Assets Disclosure [Abstract]

Summary of Goodwill and Purchased Intangible Assets



	December 31, 2017							December 31, 2016
	Gross		Accumulated Amortization			Net		Gross		Accumulated Amortization			Net
Goodwill	$	3,664	$	—		$	3,664	$	3,664	$	—		$	3,664

Other indefinite-lived intangibles	$	286	$	—		$	286	$	286	$	—		$	286
Intangibles assets with finite lives:
Patents and licensed technology	1,665		(1,436		)	229		1,665		(1,006		)	659
Total purchased intangibles	$	1,951	$	(1,436	)	$	515	$	1,951	$	(1,006	)	$	945

ACCRUED LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2017

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities

As of December 31, 2017 and 2016 accrued liabilities consists of the following (in thousands):



	December 31,
	2017		2016
Salaries, commissions, incentive compensation and benefits	$	3,608	$	4,227
Customer rebates and sales incentives	8,988		11,786
Freight	3,853		2,321
Other	5,998		4,603
Total	$	22,447	$	22,937

WARRANTY OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2017

Product Warranties Disclosures [Abstract]

Summary of Warranty Activity

The Company’s warranty activities during 2017, 2016 and 2015 were as follows (in thousands):



	December 31,
	2017			2016			2015
Balance, at beginning of year	$	31,414		$	30,547		$	33,940
Accruals for warranties issued during the year	3,797			4,130			4,383
Changes in estimates	(732		)	2,562			31
Settlements	(7,037		)	(8,523		)	(7,269		)
Increase due to accretion expense	2,053			1,772			1,001
Fair value adjustments	321			926			(1,539		)
Balance, at end of year	29,816			31,414			30,547
Less current portion	(7,427		)	(8,596		)	(7,072		)
Long-term portion	$	22,389		$	22,818		$	23,475

FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Financial Instruments Measured at Fair Value on a Recurring Basis



		December 31,
	Fair Value Hierarchy	2017		2016
Liabilities:
Warranty obligations	Level 3	$	9,790	$	10,332
Third party option to purchase receivables at a discount	Level 3	700		—

Summary of Significant Unobservable Inputs used in the Fair Value Measurements of the Company's Liabilities Designated as Level 3

As of December 31, 2017, the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows:



Item Measured at Fair Value	Valuation Technique	Description of Significant Unobservable Input	Percent Used (Weighted-Average)
Warranty obligations for microinverters sold since January 1, 2014	Discounted cash flows	Profit element and risk premium	17%
	Discounted cash flows	Credit-adjusted risk-free rate	17%
Third party option to purchase receivables at a discount	Discounted cash flows	Counter party credit-adjusted risk-free rate	4%

As of December 31, 2016, the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows:



Item Measured at Fair Value	Valuation Technique	Description of Significant Unobservable Input	Percent Used (Weighted-Average)
Warranty obligations for microinverters sold since January 1, 2014	Discounted cash flows	Profit element and risk premium	17%
	Discounted cash flows	Credit-adjusted risk-free rate	19%

Warranty obligations

Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]

Schedule of Reconciliation of Beginning and Ending Balances of Warranty Obligations/Contingent Consideration Measured at Fair Value

The following table provides a reconciliation of the beginning and ending balances of warranty obligations measured at fair value for the periods indicated (in thousands):



Balance—December 31, 2014	$	3,562
Accruals for warranties issued during period	4,140
Changes in estimates	(755		)
Settlements	(227		)
Increase due to accretion expense	1,001
Fair value adjustments	(1,539		)
Balance—December 31, 2015	$	6,182
Accruals for warranties issued during period	4,091
Changes in estimates	(1,616		)
Settlements	(1,023		)
Increase due to accretion expense	1,772
Fair value adjustments	926
Balance—December 31, 2016	$	10,332
Accruals for warranties issued during period	3,591
Changes in estimates	(4,551		)
Settlements	(1,956		)
Increase due to accretion expense	2,053
Fair value adjustments	321
Balance—December 31, 2017	$	9,790

RESTRUCTURING AND OTHER (Tables)

12 Months Ended

Dec. 31, 2017

Restructuring and Related Activities [Abstract]

Restructuring and Related Costs



	Business Divestiture
Consideration	$	1,375
Identifiable assets	(979		)
Contingent Consideration	244
Gain on business divestiture	$	640

The following table presents the details of the Company’s restructuring charges for the periods indicated (in thousands):



	Years Ended December 31,
	2017		2016			2015
Employee severance and benefit arrangements	$	2,827	$	1,263		$	—
Asset impairments	522		2,575			—
Consultants engaged in restructuring activities	12,100		—			—
Lease loss and other	1,468		579			—
Gain on business divestiture	—		(640		)	—
Total restructuring and other	$	16,917	$	3,777		$	—

Schedule of Restructuring Reserve by Type of Cost

The following table provides information regarding changes in the Company’s accrued restructuring balance for the periods indicated (in thousands):



	Employee Severance and Benefits			Asset Impairments			Lease Loss Reserves and Contractual Obligations			Total
Balance as of December 31, 2015	$	—		$	—		$	—		$	—
Charges	1,263			2,575			579			4,417
Cash payments	(1,065		)	—			(95		)	(1,160		)
Non-cash settlement	—			(2,575		)	—			(2,575		)
Balance as of December 31, 2016	$	198		$	—		$	484		$	682
Charges	2,827			522			13,568			16,917
Cash payments	(2,796		)	—			(12,958		)	(15,754		)
Non-cash settlement	—			(522		)	—			(522		)
Balance at end of period as of December 31, 2017	$	229		$	—		$	1,094		$	1,323

DEBT - (Tables)

12 Months Ended

Dec. 31, 2017

Debt Disclosure [Abstract]

Schedule of Maturities of Long-term Debt

As of December 31, 2017, the estimated schedule of principal payments due on the term loan (without regard to the February 28, 2018 amendment described above) is as follows (in thousands):



Year	Amounts
2018	$	15,715
2019	20,939
2020	13,346
Total	$	50,000

The amount of estimated schedule of principal payments due on the term loan including the impact of the February 28, 2018 amendment described above is as follows (in thousands):



Year	Amounts
2018	$	8,521
2019	25,333
2020	16,146
Total	$	50,000

Schedule of Debt

Total long-term debt was comprised of the following at December 31, 2017 and 2016 (in thousands):



	December 31, 2017			December 31, 2016
Term loan	$	50,000		$	25,000
Less unamortized discount and issuance costs	(2,111		)	(1,200		)
Carrying amount of term loan	47,889			23,800
Sale of long term financing receivable recorded as debt	2,562			—
Less value of future purchase option	(700		)	—
Carrying amount of sale of long term financing receivable recorded as debt	1,862			—
Total carrying amount of debt	49,751			23,800
Less current portion term loan	(15,715		)	(3,032		)
Less current portion of long term financing receivable recorded as debt	(1,714		)	—
Long-term debt	$	32,322		$	20,768

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2017

Commitments and Contingencies Disclosure [Abstract]

Schedule of Minimum Lease Payments Under Noncancelable Operating Leases

The Company’s minimum lease payments under noncancelable operating leases, exclusive of executory costs, as of December 31, 2017 are as follows (in thousands):



2018	$	3,011
2019	3,065
2020	2,919
2021	2,678
2022	1,973
Thereafter	1,544
Total minimum lease payments	$	15,190

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2017

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Schedule of Weighted Average Assumptions used to Estimate Fair Value of Stock Options Granted

A summary of the weighted-average assumptions used to estimate the fair values of the stock options granted during the periods presented is as follows:



	Years Ended December 31,
	2017			2016			2015
Expected term (in years)	4.4			4.5			4.5
Expected volatility	83.9		%	80.0		%	72.5		%
Annual risk-free rate of return	1.8		%	1.1		%	1.4		%
Dividend yield	—		%	—		%	—		%
Weighted-average fair value on grant date	$	0.76		$	1.29		$	4.68

Summary of Total Stock Based Compensation Expense Components

The following table summarizes the components of total stock-based compensation expense included in the consolidated statements of operations for the periods presented (in thousands):



	Years Ended December 31,
	2017		2016		2015
Cost of revenues	$	1,072	$	1,188	$	1,217
Research and development	2,573		3,879		4,559
Sales and marketing	1,157		2,144		3,162
General and administrative	1,925		3,115		3,758
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

Summary of Stock Based Compensation Expense Associated with Each Type of Award

A summary of stock-based compensation expense associated with each type of award for the periods presented is as follows (in thousands):



	Years Ended December 31,
	2017		2016		2015
Stock options and restricted stock units	$	5,559	$	8,384	$	10,685
ESPP	1,168		1,942		2,011
Total stock-based compensation expense	$	6,727	$	10,326	$	12,696

Summary of Stock Option Activity

A summary of the Company’s stock option activity for the periods presented is as follows (in thousands, except per share data):



	Shares		Weighted- Average Exercise Price per Share
Options outstanding — December 31, 2014	8,632		$	4.75
Granted	1,289		8.20
Exercised	(1,079	)	1.40
Canceled	(672	)	9.31
Options outstanding — December 31, 2015	8,170		5.36
Granted	2,440		2.12
Exercised	(375	)	0.39
Canceled	(1,505	)	6.01
Options outstanding — December 31, 2016	8,730		4.55
Granted	4,500		1.22
Exercised	(425	)	0.51
Canceled	(4,379	)	6.91
Options outstanding — December 31, 2017	8,426		1.77

Summary of Stock Options Outstanding

The following table summarizes information about stock options outstanding at December 31, 2017:



	Options Outstanding				Options Exercisable
Range of Exercise Prices	Number of Shares (in thousands)	Weighted- Average Remaining Life (in years)	Weighted- Average Exercise Price		Number of Shares (in thousands)	Weighted- Average Exercise Price
$0.27 —– $0.79	1,690	4.0	$	0.51	1,117	$	0.38
$0.83 —– $1.29	1,565	6.8	1.17		34	1.06
$1.31 —– $1.31	1,751	6.3	1.31		500	1.31
$1.37 —– $1.98	1,726	2.8	1.67		1,415	1.66
$2.00 —– $12.57	1,694	3.8	4.14		1,245	4.62
Total	8,426				4,311

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity for the periods presented is as follows: (in thousands, except per share data):



	Restricted Stock Units		Weighted Average Fair Value per Share at Grant Date
Outstanding at December 31, 2014	1,345		$	8.25
Granted	683		11.22
Vested	(488	)	8.58
Canceled	(227	)	10.32
Outstanding at December 31, 2015	1,313		9.31
Granted	54		1.99
Vested	(464	)	9.06
Canceled	(297	)	8.32
Outstanding at December 31, 2016	606		9.33
Granted	5,418		1.46
Vested	(885	)	3.81
Canceled	(1,634	)	1.90
Outstanding at December 31, 2017	3,505		2.03

Summary of ESPP Activity

A summary of ESPP activity for the years presented is as follows: (in thousands, except per share data):



	Years Ended December 31,
	2017		2016		2015
Proceeds from common stock issued under ESPP	$	313	$	999	$	2,497
Shares of common stock issued	478		659		499
Weighted-average price per share	$	0.65	$	1.52	$	5.00

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2017

Income Tax Disclosure [Abstract]

Schedule of Domestic and Foreign Components of Loss before Provision for Income Taxes

The domestic and foreign components of loss before provision for income taxes consisted of the following (in thousands):



	Years Ended December 31,
	2017			2016			2015
United States	$	(47,882	)	$	(67,631	)	$	(22,120	)
Foreign	2,541			1,644			1,417
Total	$	(45,341	)	$	(65,987	)	$	(20,703	)

Schedule of Provision for Income Taxes

The (benefit) provision for income taxes for the years presented is as follows (in thousands):



	Years Ended December 31,
	2017			2016		2015
Current:
Federal	$	—		$	—	$	—
State	21			36		44
Foreign	1,224			785		693
	1,245			821		737
Deferred:
Federal	(1,092		)	594		652
State	(21		)	59		41
Foreign	(281		)	1		(51		)
	(1,394		)	654		642
(Benefit) provision for income taxes	$	(149	)	$	1,475	$	1,379

Schedule of Effective Income Tax Rate Reconciliation



	Years Ended December 31,
	2017			2016			2015
Income tax benefit at statutory federal rate	$	(15,416	)	$	(22,435	)	$	(7,039	)
State taxes, net of federal benefit	(64		)	63			56
Change in valuation allowance	(20,571		)	21,370			7,812
Foreign tax rate and tax law differential	(133		)	27			(29		)
Tax credits	(382		)	(1,179		)	(1,553		)
Stock-based compensation	761			1,775			1,932
Other permanent items	479			776			61
Other nondeductible/nontaxable items	930			920			(72		)
Uncertain tax positions	106			158			211
Tax law changes	34,141			—			—
(Benefit) provision for income taxes	$	(149	)	$	1,475		$	1,379

Schedule of Deferred Tax Assets and Liabilities

A summary of significant components of the Company’s deferred tax assets and liabilities as of December 31, 2017 and 2016 is as follows (in thousands):



	December 31,
	2017			2016
Deferred tax assets:
Allowances and reserves	$	9,748		$	16,032
Net operating loss and tax credit carryforwards	66,243			67,875
Stock-based compensation	2,528			3,033
Deferred revenue	7,210			8,289
Fixed assets and intangibles	4,369			7,661
Other	278			2,857
Subtotal	90,376			105,747
Less valuation allowance	(88,789		)	(104,554		)
Total deferred tax assets, net of valuation allowance	1,587			1,193
Deferred tax liabilities:
Goodwill	(992		)	(1,346		)
Unremitted foreign earnings	(10		)	(748		)
Total deferred tax liabilities	(1,002		)	(2,094		)
Net deferred tax asset/(liability)	$	585		$	(901	)

Schedule of Reconciliation of Total Amounts of Unrecognized Tax Benefits

A tabular reconciliation of the total amounts of unrecognized tax benefits for the years presented is as follows (in thousands):



	Year Ended December 31,
	2017			2016			2015
Unrecognized tax benefits—at beginning of year	$	6,016		$	5,482		$	4,426
Increases in balances related to tax positions taken in prior years	—			—			14
Decreases in balances related to tax positions taken in prior years	(135		)	—			—
Increases in balances related to tax positions taken in current year	306			571			1,053
Lapses in statutes of limitations	(81		)	(37		)	(11		)
Unrecognized tax benefits—at end of year	$	6,106		$	6,016		$	5,482

NET LOSS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2017

Earnings Per Share [Abstract]

Schedule of Potential Common Shares Outstanding Excluded from the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders



	Years Ended December 31,
	2017	2016	2015
Stock options to purchase common stock	8,433	8,981	8,646
Unvested restricted stock units	3,029	906	1,506
Warrants to purchase common stock	1,083	—	111
Total	12,545	9,887	10,263

SEGMENT AND GEOGRAPHIC INFORMATION (Tables)

12 Months Ended

Dec. 31, 2017

Segment Reporting [Abstract]

Summary of Net Revenues and Long-Lived Assets by Geographic Region

The following tables present net revenues (based on the destination of shipments) and long-lived assets by geographic region as of and for the periods presented (in thousands):

Net Revenues



	Years Ended December 31,
	2017		2016		2015
United States	$	199,565	$	259,080	$	303,195
International	86,601		63,511		54,054
Total	$	286,166	$	322,591	$	357,249

Long-Lived Assets



	As of December 31,
	2017		2016		2015
United States	$	16,899	$	22,634	$	21,913
China	7,164		5,727		7,950
Other	2,420		3,079		2,255
Total	$	26,483	$	31,440	$	32,118

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) (Tables)

12 Months Ended

Dec. 31, 2017

Quarterly Financial Information Disclosure [Abstract]

Schedule of Quarterly Financial Information

The following tables show a summary of the Company’s quarterly financial information for each of the four quarters of 2017 and 2016 (in thousands, except per share data):



	Year Ended December 31, 2017
	March 31			June 30			September 30			December 31

Net revenues	$	54,751		$	74,704		$	77,038		$	79,674
Cost of revenues	47,703			61,157			60,577			60,685
Gross profit	7,048			13,547			16,461			18,989
Operating expenses:
Research and development	9,605			7,947			7,397			8,208
Sales and marketing	6,458			6,274			5,453			4,940
General and administrative	5,833			4,964			5,441			5,983
Restructuring charges	7,247			3,609			4,071			1,991
Total operating expenses	29,143			22,794			22,362			21,122
Loss from operations	(22,095		)	(9,247		)	(5,901		)	(2,133		)
Other income expense, net	(1,079		)	(1,992		)	(1,137		)	(1,755		)
Loss before income taxes	(23,174		)	(11,239		)	(7,038		)	(3,888		)
Income tax benefit (provision)	(131		)	(854		)	184			948
Net loss	$	(23,305	)	$	(12,093	)	$	(6,854	)	$	(2,940	)
Net loss per share, basic and diluted	$	(0.30	)	$	(0.14	)	$	(0.08	)	$	(0.03	)

	Year Ended December 31, 2016
	March 31			June 30			September 30			December 31
Net revenues	$	64,121		$	79,185		$	88,684		$	90,601
Cost of revenues	52,361			65,049			72,805			74,367
Gross profit	11,760			14,136			15,879			16,234
Operating expenses:
Research and development	13,066			13,091			13,169			11,378
Sales and marketing	10,215			9,987			11,016			7,592
General and administrative	7,567			6,846			6,708			6,296
Restructuring charges	—			—			2,717			1,060
Total operating expenses	30,848			29,924			33,610			26,326
Loss from operations	(19,088		)	(15,788		)	(17,731		)	(10,092		)
Other income expense, net	529			(591		)	(881		)	(2,345		)
Loss before income taxes	(18,559		)	(16,379		)	(18,612		)	(12,437		)
Income tax provision	(236		)	(344		)	(144		)	(751		)
Net loss	$	(18,795	)	$	(16,723	)	$	(18,756	)	$	(13,188	)
Net loss per share, basic and diluted	$	(0.41	)	$	(0.36	)	$	(0.40	)	$	(0.21	)

DESCRIPTION OF BUSINESS - Narrative (Details) system in Thousands, microinverter in Millions, watt in Billions	Dec. 31, 2017 system watt microinverter	Mar. 31, 2016 country
Microinverter
Product Information [Line Items]
Number of product shipped, more than \| microinverter	16
Gigawatts, over \| watt	3
Residential and Commercial Systems
Product Information [Line Items]
Number of product deployed, more than \| system	739
Number of countries in which product is deployed, over \| country		100

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)			1 Months Ended	3 Months Ended								12 Months Ended
	Feb. 28, 2018	Feb. 04, 2018 USD ($)	Feb. 28, 2018 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Sep. 30, 2017 USD ($) $ / shares	Jun. 30, 2017 USD ($) $ / shares	Mar. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($) $ / shares	Sep. 30, 2016 USD ($) $ / shares	Jun. 30, 2016 USD ($) $ / shares	Mar. 31, 2016 USD ($) $ / shares	Dec. 31, 2017 USD ($) deliverable factor $ / shares	Dec. 31, 2016 USD ($) $ / shares	Dec. 31, 2015 USD ($) $ / shares	Dec. 31, 2014 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Ongoing reduction in operating expense												$ 38,400,000
Restructuring and other charges				$ 1,991,000	$ 4,071,000	$ 3,609,000	$ 7,247,000	$ 1,060,000	$ 2,717,000	$ 0	$ 0	16,917,000	$ 3,777,000	$ 0
Proceeds from issuance of common stock												26,425,000	16,142,000	0
Increase to revenue				79,674,000	77,038,000	74,704,000	54,751,000	90,601,000	88,684,000	79,185,000	64,121,000	286,166,000	322,591,000	357,249,000
Increase to earnings				$ (2,940,000)	$ (6,854,000)	$ (12,093,000)	$ (23,305,000)	$ (13,188,000)	$ (18,756,000)	$ (16,723,000)	$ (18,795,000)	$ (45,192,000)	$ (67,462,000)	$ (22,082,000)
Reduction of net loss per share (in usd per share) \| $ / shares				$ (0.03)	$ (0.08)	$ (0.14)	$ (0.30)	$ (0.21)	$ (0.40)	$ (0.36)	$ (0.41)	$ (0.54)	$ (1.34)	$ (0.49)
Allowance for doubtful accounts				$ 2,378,000				$ 2,921,000				$ 2,378,000	$ 2,921,000	$ 1,808,000	$ 569,000
Asset impairments												800,000	2,600,000
Goodwill, impairment loss												0	0	0
Impairment of intangible assets												$ 0	0	0
Number of factors considered in estimating replacement cost \| factor												3
Research and development expense				8,208,000	$ 7,397,000	$ 7,947,000	$ 9,605,000	11,378,000	$ 13,169,000	$ 13,091,000	$ 13,066,000	$ 33,157,000	50,703,000	$ 50,819,000
Stock-based compensation requisite service period												4 years
Increase in accumulated deficit				295,727,000				250,535,000				$ 295,727,000	250,535,000
Increase in accrued liabilities				22,447,000				$ 22,937,000				$ 22,447,000	$ 22,937,000
Envoy Communications Gateway Device and Enlighten Web-Based Monitoring Service
Fair Value, Option, Quantitative Disclosures [Line Items]
Revenue recognition, number of deliverables \| deliverable												2
First and Second Generation
Fair Value, Option, Quantitative Disclosures [Line Items]
Product warranty, term												15 years
Third and Fourth Generation
Fair Value, Option, Quantitative Disclosures [Line Items]
Product warranty, term												25 years
Envoy Communications Gateway
Fair Value, Option, Quantitative Disclosures [Line Items]
Product warranty, term												5 years
AC Battery Storage Solution
Fair Value, Option, Quantitative Disclosures [Line Items]
Product warranty, term												10 years
Minimum
Fair Value, Option, Quantitative Disclosures [Line Items]
Property and equipment estimated useful life												3 years
Intangible assets, estimated useful life												3 years
Product warranty, term												15 years
Product installation period												3 months
Period failure rate measurement lags product sale												3 months
Maximum
Fair Value, Option, Quantitative Disclosures [Line Items]
Property and equipment estimated useful life												10 years
Intangible assets, estimated useful life												5 years
Product warranty, term												25 years
Product installation period												9 months
Period failure rate measurement lags product sale												9 months
Product concentration risk \| Revenue \| Enlighten
Fair Value, Option, Quantitative Disclosures [Line Items]
Percent of revenue represented by product line or service, less than												2.00%
Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606 \| Enlighten
Fair Value, Option, Quantitative Disclosures [Line Items]
Revenue recognition period												6 years 6 months
Subsequent Event \| Private Placement
Fair Value, Option, Quantitative Disclosures [Line Items]
Proceeds from issuance of common stock		$ 20,000,000	$ 20,000,000
Second amendment to term loans \| Secured Debt \| Subsequent Event
Fair Value, Option, Quantitative Disclosures [Line Items]
Percent decrease in principal payments	50.00%		50.00%
Service period \| Envoy Communications Gateway Device and Enlighten Web-Based Monitoring Service
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase to revenue				2,600,000
Increase to earnings				$ 2,600,000
Reduction of net loss per share (in usd per share) \| $ / shares				$ 0.03
Service period \| Minimum \| Enlighten
Fair Value, Option, Quantitative Disclosures [Line Items]
Property and equipment estimated useful life				6 years 6 months
Service period \| Maximum \| Enlighten
Fair Value, Option, Quantitative Disclosures [Line Items]
Property and equipment estimated useful life				10 years
Pro Forma \| Accounting Standards Update 2014-09 \| Difference between Revenue Guidance in Effect before and after Topic 606
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase in deferred revenue				$ 77,000,000								$ 77,000,000
Increase in deferred costs				43,000,000								43,000,000
Increase in accumulated deficit				34,000,000								34,000,000
Pro Forma \| Accounting Standards Update 2014-09, Contra Revenue \| Difference between Revenue Guidance in Effect before and after Topic 606
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase in accumulated deficit				6,000,000								6,000,000
Increase in accrued liabilities				6,000,000								6,000,000
Pro Forma \| Accounting Standards Update 2014-09, Capitalization And Amortization Contract Acquisition Costs \| Difference between Revenue Guidance in Effect before and after Topic 606
Fair Value, Option, Quantitative Disclosures [Line Items]
Increase in accumulated deficit				800,000								800,000
Increase in deferred costs, commissions				$ 800,000								$ 800,000

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Activity in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, at beginning of year	$ 2,921	$ 1,808	$ 569
Net charges to expenses	476	3,097	1,502
Write-offs, net of recoveries	(1,019)	(1,984)	(263)
Balance, at end of year	$ 2,378	$ 2,921	$ 1,808

INVENTORY - Summary of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Inventory Disclosure [Abstract]
Raw materials	$ 2,341	$ 5,095
Finished goods	23,658	26,865
Total inventory	$ 25,999	$ 31,960

PROPERTY AND EQUIPMENT, NET - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 70,921	$ 71,110
Less accumulated depreciation and amortization	(44,438)	(39,670)
Property and equipment, net	$ 26,483	31,440
Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	10 years
Equipment and machinery
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 41,148	38,486
Equipment and machinery \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Equipment and machinery \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	10 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,188	2,635
Furniture and fixtures \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Furniture and fixtures \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	7 years
Computer equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,627	2,913
Computer equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Computer equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Capitalized software costs
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,749	11,324
Capitalized software costs \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	3 years
Capitalized software costs \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	5 years
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 8,537	9,477
Leasehold improvements \| Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	4 years
Leasehold improvements \| Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (Years)	10 years
Construction in process
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,672	$ 6,275

PROPERTY AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 8.6	$ 10.0	$ 8.1
Unamortized capitalized software costs	$ 1.1	$ 1.9

GOODWILL AND INTANGIBLE ASSETS - Summary of Goodwill and Purchased Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Finite-Lived Intangible Assets [Line Items]
Goodwill, gross	$ 3,664	$ 3,664
Goodwill	3,664	3,664
Other indefinite-lived intangibles	286	286
Intangibles assets with finite lives:
Total purchased intangibles, gross	1,951	1,951
Total purchased intangibles, accumulated amortization	(1,436)	(1,006)
Total purchased intangibles, net	515	945
Patents and licensed technology
Intangibles assets with finite lives:
Gross	1,665	1,665
Accumulated Amortization	(1,436)	(1,006)
Total	$ 229	$ 659

GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		12 Months Ended
	Oct. 31, 2015	Jul. 31, 2014	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Aggregate amortization expense			$ 0.4	$ 0.7	$ 0.5
ASIC
Finite-Lived Intangible Assets [Line Items]
Licensed technology term	3 years
Patents
Finite-Lived Intangible Assets [Line Items]
Intangible assets, estimated useful life		3 years
Patents and licensed technology
Finite-Lived Intangible Assets [Line Items]
Patents and licensed technology amortized in 2018			$ 0.2

ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Accrued Liabilities [Abstract]
Salaries, commissions, incentive compensation and benefits	$ 3,608	$ 4,227
Customer rebates and sales incentives	8,988	11,786
Freight	3,853	2,321
Other	5,998	4,603
Total	$ 22,447	$ 22,937

WARRANTY OBLIGATIONS - Summary of Warranty Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Changes in the Company's product warranty liability
Balance, at beginning of year	$ 31,414	$ 30,547	$ 33,940
Accruals for warranties issued during the year	3,797	4,130	4,383
Changes in estimates	(732)	2,562	31
Settlements	(7,037)	(8,523)	(7,269)
Increase due to accretion expense	2,053	1,772	1,001
Fair value adjustments	321	926	(1,539)
Balance, at end of year	29,816	31,414	30,547
Less current portion	(7,427)	(8,596)	(7,072)
Long-term portion	$ 22,389	$ 22,818	$ 23,475

WARRANTY OBLIGATIONS - Narrative (Details) microinverter in Millions, $ in Millions	12 Months Ended			42 Months Ended	54 Months Ended
	Dec. 31, 2017 USD ($) microinverter	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2015 microinverter	Dec. 31, 2017 microinverter	Jun. 30, 2012 microinverter
Second generation
Product Liability Contingency [Line Items]
Number of units sold \| microinverter						1.0
Second generation \| Labor reimbursement cost
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates \| $	$ (1.9)	$ 1.5	$ 0.7
Second generation \| Failure rate
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates \| $	3.9	3.0	0.8
Sixth generation \| Replacement cost
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates \| $	$ (2.2)	$ (2.1)
Third generation
Product Liability Contingency [Line Items]
Number of units sold \| microinverter				3.9
Fourth generation
Product Liability Contingency [Line Items]
Number of units sold \| microinverter					10.2
Fourth generation \| Replacement cost
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates \| $			$ (1.5)
IQ Series
Product Liability Contingency [Line Items]
Number of units sold \| microinverter	1.2

FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - Recurring - Level 3 - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Warranty obligations
Liabilities:
Warranty obligations/ Third party option to purchase receivables at a discount	$ 9,790	$ 10,332	$ 6,182	$ 3,562
Third party option to purchase receivables at a discount
Liabilities:
Warranty obligations/ Third party option to purchase receivables at a discount	$ 700	$ 0

FAIR VALUE MEASUREMENTS - Schedule of Reconciliation of Beginning and Ending Balances of Warranty Obligations Measured at Fair Value (Details) - Recurring - Level 3 - Warranty obligations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Warranty Obligations at Fair Value [Roll Forward]
Beginning balance	$ 10,332	$ 6,182	$ 3,562
Accruals for warranties issued during period	3,591	4,091	4,140
Changes in estimates	(4,551)	(1,616)	(755)
Settlements	(1,956)	(1,023)	(227)
Increase due to accretion expense	2,053	1,772	1,001
Fair value adjustments	321	926	(1,539)
Ending balance	$ 9,790	$ 10,332	$ 6,182

FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2017 USD ($)
Derivative [Line Items]
Value of future purchase option	$ 700
Warranty obligations \| Discounted cash flows \| Recurring \| Level 3
Derivative [Line Items]
Decrease to fair value measurement as a result of 100 basis point increase	443
Increase to fair value measurement as a result of 100 basis point decrease	$ 485

FAIR VALUE MEASUREMENTS - Summary of Significant Unobservable Inputs used in the Fair Value Measurements of the Company's Liabilities Designated as Level 3 (Details) - Recurring - Level 3 - Discounted cash flows	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Warranty obligations for microinverters sold since January 1, 2014
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Profit element and risk premium	17.00%	17.00%
Credit-adjusted risk-free rate	17.00%	19.00%
Third party option to purchase receivables at a discount
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Counter party credit-adjusted risk-free rate	4.00%

RESTRUCTURING AND OTHER - Schedule Restructuring Charges (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Employee severance and benefit arrangements	$ 2,827	$ 1,263	$ 0
Asset impairments	522	2,575	0
Consultants engaged in restructuring activities	12,100	0	0
Lease loss and other	1,468	579	0
Gain on business divestiture	0	(640)	0
Total restructuring and other	$ 16,917	$ 3,777	$ 0

RESTRUCTURING AND OTHER - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring Cost and Reserve [Line Items]
Charges	$ 1,991	$ 4,071	$ 3,609	$ 7,247	$ 1,060	$ 2,717	$ 0	$ 0	$ 16,917	$ 3,777	$ 0
Restructuring Plan 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning				682				0	682	0
Charges									16,917	4,417
Cash payments									(15,754)	(1,160)
Non-cash settlement									(522)	(2,575)
Restructuring reserve, ending	1,323				682				1,323	682	0
Employee Severance and Benefits \| Restructuring Plan 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning				198				0	198	0
Charges									2,827	1,263
Cash payments									(2,796)	(1,065)
Non-cash settlement									0	0
Restructuring reserve, ending	229				198				229	198	0
Asset Impairments \| Restructuring Plan 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning				0				0	0	0
Charges									522	2,575
Cash payments									0	0
Non-cash settlement									(522)	(2,575)
Restructuring reserve, ending	0				0				0	0	0
Lease Loss Reserves and Contractual Obligations \| Restructuring Plan 2016
Restructuring Cost and Reserve [Line Items]
Restructuring reserve, beginning				$ 484				$ 0	484	0
Charges									13,568	579
Cash payments									(12,958)	(95)
Non-cash settlement									0	0
Restructuring reserve, ending	$ 1,094				$ 484				$ 1,094	$ 484	$ 0

RESTRUCTURING AND OTHER - Gain on business divestiture (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restructuring and Related Activities [Abstract]
Consideration		$ 1,375
Identifiable assets		(979)
Contingent Consideration		244
Gain on business divestiture	$ 0	$ 640	$ 0

DEBT - Term Loan (Details)		1 Months Ended			12 Months Ended
DEBT - Term Loan (Details)	Feb. 28, 2018	Feb. 28, 2018	Feb. 28, 2017 USD ($) $ / shares shares	Jul. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) $ / shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Line of Credit Facility [Line Items]
Repayments of lines of credit					$ 10,100,000	$ 16,900,000	$ 29,150,000
Warrants not settleable in cash					$ 1,400,000
Tennenbaum Capital Partners, LLC \| Secured Debt
Line of Credit Facility [Line Items]
Debt instrument principal amount				$ 25,000,000.0
Proceeds from term loan, net of issuance costs				$ 25,000,000
Line of credit facility, interest rate during period				10.25%
Commitment fee percentage				3.30%
Closing fee, percentage				10.00%
LIBOR \| Tennenbaum Capital Partners, LLC \| Secured Debt
Line of Credit Facility [Line Items]
Line of credit facility, interest rate during period				9.5625%
Reduction of interest rate during period, percent				1.00%
Minimum \| Tennenbaum Capital Partners, LLC \| Secured Debt
Line of Credit Facility [Line Items]
Prepayment fee, percent				1.00%
Maximum \| Tennenbaum Capital Partners, LLC \| Secured Debt
Line of Credit Facility [Line Items]
Prepayment fee, percent				3.00%
Amended Term Loan Agreement \| Tennenbaum Capital Partners, LLC \| Secured Debt
Line of Credit Facility [Line Items]
Debt instrument principal amount			$ 25,000,000.0
Secured Debt \| Amended Term Loan Agreement \| Tennenbaum Capital Partners, LLC
Line of Credit Facility [Line Items]
Line of credit facility, interest rate during period			10.3125%
Commitment fee percentage			3.00%
Closing fee, percentage			4.00%
Unrestricted cash requirement, minimum			$ 10,000,000.0
Number of securities called by warrants (shares) \| shares			1,220,000
Warrant to purchase common stock, price per share (usd per share) \| $ / shares			$ 1.05
Class of warrant term year			7 years
Secured Debt \| Amended Term Loan Agreement \| LIBOR \| Tennenbaum Capital Partners, LLC
Line of Credit Facility [Line Items]
Basis spread on variable rate			9.25%
Secured Debt \| Amended Term Loan Agreement \| Minimum \| Tennenbaum Capital Partners, LLC
Line of Credit Facility [Line Items]
Prepayment fee, percent			1.00%
Secured Debt \| Amended Term Loan Agreement \| Maximum \| Tennenbaum Capital Partners, LLC
Line of Credit Facility [Line Items]
Prepayment fee, percent			3.00%
Secured Debt \| Term Loan Agreement, July 2016 \| Tennenbaum Capital Partners, LLC
Line of Credit Facility [Line Items]
Debt instrument principal amount				$ 25,000,000.0
Line of Credit \| Wells Fargo Bank \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Repayments of lines of credit			$ 10,100,000	$ 10,300,000
Closing date to March 31, 2018 \| Secured Debt \| Amended Term Loan Agreement
Line of Credit Facility [Line Items]
Liquidity ratio required			1.5
April 1, 2019 and thereafter \| Secured Debt \| Amended Term Loan Agreement
Line of Credit Facility [Line Items]
Liquidity ratio required			1.75
Warrants Not Settleable in Cash
Line of Credit Facility [Line Items]
Warrant to purchase common stock, price per share (usd per share) \| $ / shares					$ 1.05
Common stock issued, price per share (usd per share) \| $ / shares					$ 1.56
Expected volatility rate					85.90%
Risk free interest rate					2.23%
Expected dividend rate					0.00%
Expected term					7 years
Subsequent Event \| Second amendment to term loans \| Secured Debt
Line of Credit Facility [Line Items]
Percent decrease in principal payments	50.00%	50.00%

DEBT - Maturity Schedule (Details) - Secured Debt - USD ($) $ in Thousands	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2016
Term Loan Agreement, July 2016
Debt Instrument [Line Items]
2018		$ 15,715
2019		20,939
2020		13,346
Total		$ 50,000	$ 25,000
Subsequent Event \| Second amendment to term loans
Debt Instrument [Line Items]
2018	$ 8,521
2019	25,333
2020	16,146
Total	$ 50,000

DEBT - Sale of Long Term Financing Receivables (Details) $ in Millions	1 Months Ended
	Dec. 31, 2017 USD ($)
Line of Credit Facility [Line Items]
Value of future purchase option	$ 0.7
Financing Receivable Recorded As Debt \| Financing Receivable
Line of Credit Facility [Line Items]
Proceeds from term loan, net of issuance costs	$ 2.8

DEBT - Long-term debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Carrying amount of debt	$ 49,751	$ 23,800
Long-term debt	32,322	20,768
Secured Debt \| Term Loan Agreement, July 2016
Debt Instrument [Line Items]
Long-term debt gross	50,000	25,000
Less unamortized discount and issuance costs	(2,111)	(1,200)
Carrying amount of debt	47,889	23,800
Less current portion	(15,715)	(3,032)
Financing Receivable \| Financing Receivable Recorded As Debt
Debt Instrument [Line Items]
Long-term debt gross	2,562	0
Less value of future purchase option	(700)	0
Carrying amount of debt	1,862	0
Less current portion	$ (1,714)	$ 0

DEBT - Revolving Credit Facility (Details) - USD ($)	1 Months Ended		12 Months Ended
DEBT - Revolving Credit Facility (Details) - USD ($)	Feb. 28, 2017	Jul. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 18, 2015	Nov. 30, 2012
Line of Credit Facility [Line Items]
Revolving credit facility			$ 0	$ 10,100,000
Repayments of lines of credit			$ 10,100,000	16,900,000	$ 29,150,000
Line of Credit \| Wells Fargo Bank \| Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity							$ 50,000,000.0
Accordion feature						$ 25,000,000.0
Revolving credit facility				$ 10,100,000
Repayments of lines of credit	$ 10,100,000	$ 10,300,000

- Definition

The carrying value as of the balance sheet date of the current portion of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References + Details

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 2.8	$ 3.8	$ 3.2
Purchase obligation	$ 26.9

COMMITMENTS AND CONTINGENCIES - Schedule of Minimum Lease Payments Under Noncancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2017 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2018	$ 3,011
2019	3,065
2020	2,919
2021	2,678
2022	1,973
Thereafter	1,544
Total minimum lease payments	$ 15,190

SALE OF COMMON STOCK (Details) - USD ($) $ in Thousands, shares in Millions	1 Months Ended		3 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2016	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsidiary, Sale of Stock [Line Items]
Issuance of common stock, net of offering costs				$ 26,425	$ 15,924
Proceeds from issuance of common stock				$ 26,425	$ 16,142	$ 0
Private Placement
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (shares)	10.8
Gross proceeds from issuance of common stock	$ 10,000
At The Market Issuance Sales Agreement (ATM)
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued (shares)			11.1
Issuance of common stock, net of offering costs		$ 17,000
Proceeds from issuance of common stock			$ 16,600

STOCK-BASED COMPENSATION - Narrative (Details)				12 Months Ended
STOCK-BASED COMPENSATION - Narrative (Details)	Jan. 01, 2018 shares	May 18, 2017 shares	Apr. 03, 2017 shares	Dec. 31, 2017 USD ($) purchase_period $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares	Jan. 01, 2017 shares	Dec. 31, 2014 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (shares)				8,426,000	8,730,000	8,170,000		8,632,000
Total unrecognized compensation cost \| $				$ 10,400,000
Weighted-average period				3 years
Income tax benefit recognized relating to stock-based compensation expense \| $				$ 0
Income tax benefit realized from exercised stock options \| $				0
Intrinsic value of options exercised \| $				$ 500,000	$ 700,000	$ 4,900,000
Number of options outstanding that were vested and expected to vest (shares)				8,400,000
Weighted-average fair value, vested (usd per share) \| $ / shares				$ 1.77
Weighted-average remaining contractual term, vested				4 years 8 months 12 days
Aggregate intrinsic value, exercisable shares \| $				$ 4,000,000
Number of shares exercisable (shares)				4,311,000
Common stock fair value (usd per share) \| $ / shares				$ 2.41
Common stock to be purchased in exchange for options (in shares)				4,379,000	1,505,000	672,000
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Replacement awards of restricted stock units (in shares)				5,418,000	54,000	683,000
Intrinsic value of units vested \| $				$ 900,000	$ 900,000	$ 4,200,000
Weighted average remaining contractual term				3 years 1 month 6 days
Intrinsic value of restricted stock units outstanding \| $				$ 8,400,000
2006 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards granted period, vest over				4 years
Equity awards granted contractual term				10 years
Options outstanding (shares)				2,300,000
Number of shares available for issuance (shares)				0
2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards granted period, vest over				4 years
Number of shares available for issuance (shares)				743,329
Issue of common stock (shares)				2,643,171
Increase on each January 1 in number of shares of common stock reserved for issuance under the stock incentive plan				4.50%
2011 Plan \| Before August 1, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expiration term of ESPP				10 years
2011 Plan \| After August 1, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Equity awards granted contractual term				7 years
2011 Employee Stock Purchase Plan (ESPP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for issuance (shares)				290,658
Issue of common stock (shares)				669,603
Increase in shares authorized for issuance under plan (shares)		400,000
Annual share increase in reserved shares on each January 1 (shares)				330,396			330,396
Increase in shares authorized as a percentage of the total number of shares of common stock outstanding				1.00%
Number of interim purchase periods, up to \| purchase_period				4
General duration (months) of employee stock purchase plan				24 months
Payroll deductions				15.00%
Fair market value				85.00%
Look-back feature in ESPP				2 years
Recognition period for additional expense triggered by the reset feature				24 months
Purchase of common stock limit \| $				$ 25,000
Tender Offer, Exchange Out Of The Money Stock Options For Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be purchased in exchange for options (in shares)			2,362,470
Replacement awards of restricted stock units (in shares)			733,559
Subsequent Event \| 2011 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares authorized for issuance under plan (shares)	3,866,120
Subsequent Event \| 2011 Employee Stock Purchase Plan (ESPP)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual share increase in reserved shares on each January 1 (shares)	700,000

STOCK-BASED COMPENSATION - Schedule of Weighted Average Assumptions used to Estimate Fair Value of Stock Options Granted (Details) - Stock options - $ / shares	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
The Fair Value of Each Option Granted During the Period [Abstract]
Expected term (in years)	4 years 4 months 13 days	4 years 6 months	4 years 6 months
Expected volatility	83.90%	80.00%	72.50%
Annual risk-free rate of return	1.80%	1.10%	1.40%
Dividend yield	0.00%	0.00%	0.00%
Weighted-average fair value on grant date (usd per share)	$ 0.76	$ 1.29	$ 4.68

STOCK-BASED COMPENSATION - Summary of Total Stock Based Compensation Expense Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,727	$ 10,326	$ 12,696
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,072	1,188	1,217
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,573	3,879	4,559
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,157	2,144	3,162
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,925	$ 3,115	$ 3,758

STOCK-BASED COMPENSATION - Summary of Stock Based Compensation Expense Associated with Each Type of Award (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,727	$ 10,326	$ 12,696
Stock options and restricted stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	5,559	8,384	10,685
ESPP
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,168	$ 1,942	$ 2,011

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Options outstanding, beginning (shares)	8,730	8,170	8,632
Granted (shares)	4,500	2,440	1,289
Exercised (shares)	(425)	(375)	(1,079)
Canceled (shares)	(4,379)	(1,505)	(672)
Options outstanding, ending (shares)	8,426	8,730	8,170
Weighted- Average Exercise Price per Share
Options outstanding, beginning (usd per share)	$ 4.55	$ 5.36	$ 4.75
Granted (usd per share)	1.22	2.12	8.20
Exercised (usd per share)	0.51	0.39	1.40
Canceled (usd per share)	6.91	6.01	9.31
Options outstanding, ending (usd per share)	$ 1.77	$ 4.55	$ 5.36

STOCK-BASED COMPENSATION - Summary of Stock Options Outstanding (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2017 $ / shares shares
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Options Outstanding - Number of Shares (shares) \| shares	8,426
Options Outstanding - Weighted- Average Remaining Life
Options Outstanding - Weighted- Average Exercise Price (usd per share)
Options Exercisable - Number of Shares Exercisable (shares) \| shares	4,311
Options Exercisable - Weighted- Average Exercise Price (usd per share)
$0.27 – $1.63
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Range of Exercise Prices - Lower Range Limit (usd per share)	0.27
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 0.79
Options Outstanding - Number of Shares (shares) \| shares	1,690
Options Outstanding - Weighted- Average Remaining Life	4 years
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 0.51
Options Exercisable - Number of Shares Exercisable (shares) \| shares	1,117
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 0.38
$1.88 - $6.90
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Range of Exercise Prices - Lower Range Limit (usd per share)	0.83
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 1.29
Options Outstanding - Number of Shares (shares) \| shares	1,565
Options Outstanding - Weighted- Average Remaining Life	6 years 9 months 18 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 1.17
Options Exercisable - Number of Shares Exercisable (shares) \| shares	34
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 1.06
$6.98 – $8.57
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Range of Exercise Prices - Lower Range Limit (usd per share)	1.31
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 1.31
Options Outstanding - Number of Shares (shares) \| shares	1,751
Options Outstanding - Weighted- Average Remaining Life	6 years 3 months 18 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 1.31
Options Exercisable - Number of Shares Exercisable (shares) \| shares	500
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 1.31
$8.58 - $15.15
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Range of Exercise Prices - Lower Range Limit (usd per share)	1.37
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 1.98
Options Outstanding - Number of Shares (shares) \| shares	1,726
Options Outstanding - Weighted- Average Remaining Life	2 years 9 months 18 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 1.67
Options Exercisable - Number of Shares Exercisable (shares) \| shares	1,415
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 1.66
$16.01 - $16.01
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Range of Exercise Prices - Lower Range Limit (usd per share)	2.00
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 12.57
Options Outstanding - Number of Shares (shares) \| shares	1,694
Options Outstanding - Weighted- Average Remaining Life	3 years 9 months 18 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 4.14
Options Exercisable - Number of Shares Exercisable (shares) \| shares	1,245
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 4.62

STOCK-BASED COMPENSATION - Summary of Restricted Stock Unit Activity (Details) - Restricted stock units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Units
Outstanding units, beginning (shares)	606	1,313	1,345
Granted (shares)	5,418	54	683
Vested (shares)	(885)	(464)	(488)
Canceled (shares)	(1,634)	(297)	(227)
Outstanding units, ending (shares)	3,505	606	1,313
Weighted Average Fair Value per Share at Grant Date
Outstanding units, beginning (usd per share)	$ 9.33	$ 9.31	$ 8.25
Granted (usd per share)	1.46	1.99	11.22
Vested (usd per share)	3.81	9.06	8.58
Canceled (usd per share)	1.90	8.32	10.32
Outstanding units, ending (usd per share)	$ 2.03	$ 9.33	$ 9.31

STOCK-BASED COMPENSATION - Summary of ESPP Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Proceeds from common stock issued under ESPP	$ 313	$ 999	$ 2,497
Shares of common stock issued (shares)	478	659	499
Weighted-average price per share (usd per share)	$ 0.65	$ 1.52	$ 5.00

INCOME TAXES - Schedule of Domestic and Foreign Components of Loss before Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
United States									$ (47,882)	$ (67,631)	$ (22,120)
Foreign									2,541	1,644	1,417
Loss before income taxes	$ (3,888)	$ (7,038)	$ (11,239)	$ (23,174)	$ (12,437)	$ (18,612)	$ (16,379)	$ (18,559)	$ (45,341)	$ (65,987)	$ (20,703)

INCOME TAXES - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Federal									$ 0	$ 0	$ 0
State									21	36	44
Foreign									1,224	785	693
Total									1,245	821	737
Deferred:
Federal									(1,092)	594	652
State									(21)	59	41
Foreign									(281)	1	(51)
Total									(1,394)	654	642
(Benefit) provision for income taxes	$ (948)	$ (184)	$ 854	$ 131	$ 751	$ 144	$ 344	$ 236	$ (149)	$ 1,475	$ 1,379

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Operating Loss Carryforwards [Line Items]
Federal statutory income tax rate percent	34.00%
Valuation allowance on its U.S. and state deferred tax assets	$ 88,789	$ 104,554
Decrease in valuation allowance	15,800
Reduction in deferred tax assets	28,300
Increase to unrecognized tax benefits	100
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	176,200
Federal \| Research tax credit carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	11,300
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	89,100
State \| Research tax credit carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	$ 11,700

INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax benefit at statutory federal rate									$ (15,416)	$ (22,435)	$ (7,039)
State taxes, net of federal benefit									(64)	63	56
Change in valuation allowance									(20,571)	21,370	7,812
Foreign tax rate and tax law differential									(133)	27	(29)
Tax credits									(382)	(1,179)	(1,553)
Stock-based compensation									761	1,775	1,932
Other permanent items									479	776	61
Other nondeductible/nontaxable items									930	920	(72)
Uncertain tax positions									106	158	211
Tax law changes									34,141	0	0
(Benefit) provision for income taxes	$ (948)	$ (184)	$ 854	$ 131	$ 751	$ 144	$ 344	$ 236	$ (149)	$ 1,475	$ 1,379

INCOME TAXES - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred tax assets:
Allowances and reserves	$ 9,748	$ 16,032
Net operating loss and tax credit carryforwards	66,243	67,875
Stock-based compensation	2,528	3,033
Deferred revenue	7,210	8,289
Fixed assets and intangibles	4,369	7,661
Other	278	2,857
Subtotal	90,376	105,747
Less valuation allowance	(88,789)	(104,554)
Total deferred tax assets, net of valuation allowance	1,587	1,193
Deferred tax liabilities:
Goodwill	(992)	(1,346)
Unremitted foreign earnings	(10)	(748)
Total deferred tax liabilities	(1,002)	(2,094)
Net deferred tax asset	$ 585
Net deferred tax liability		$ (901)

INCOME TAXES - Schedule of Reconciliation of Total Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits—at beginning of year	$ 6,016	$ 5,482	$ 4,426
Increases in balances related to tax positions taken in prior years	0	0	14
Decreases in balances related to tax positions taken in prior years	(135)	0	0
Increases in balances related to tax positions taken in current year	306	571	1,053
Lapses in statutes of limitations	(81)	(37)	(11)
Unrecognized tax benefits—at end of year	$ 6,106	$ 6,016	$ 5,482

CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS - Narrative (Details)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Customer Accounting for the largest concentration of accounts payable \| Accounts receivable \| Credit concentration risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk	22.00%	25.00%
Customer accounting for the largest concentration of revenue \| Net revenue \| Customer concentration risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk	15.00%	18.00%	17.00%
Customer accounting for second largest concentration of revenue \| Net revenue \| Customer concentration risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk	11.00%		12.00%

NET LOSS PER SHARE - Schedule of Potential Common Shares Outstanding Excluded from the Computation of Diluted Net Loss Per Share Attributable to Common Stockholders (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	12,545	9,887	10,263
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	8,433	8,981	8,646
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	3,029	906	1,506
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	1,083	0	111

SEGMENT AND GEOGRAPHIC INFORMATION - Narrative (Details)	12 Months Ended
	Dec. 31, 2017 business_activity segment
Segment Reporting [Abstract]
Number of business activities \| business_activity	1
Number of operating segments	1
Number of reportable segments	1

SEGMENT AND GEOGRAPHIC INFORMATION - Summary of Net Revenues by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues	$ 79,674	$ 77,038	$ 74,704	$ 54,751	$ 90,601	$ 88,684	$ 79,185	$ 64,121	$ 286,166	$ 322,591	$ 357,249
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									199,565	259,080	303,195
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Net revenues									$ 86,601	$ 63,511	$ 54,054

SEGMENT AND GEOGRAPHIC INFORMATION - Summary of Long-Lived Assets by Geographic Region (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	$ 26,483	$ 31,440	$ 32,118
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	16,899	22,634	21,913
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	7,164	5,727	7,950
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	$ 2,420	$ 3,079	$ 2,255

QUARTERLY FINANCIAL INFORMATION (UNAUDITED) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 79,674	$ 77,038	$ 74,704	$ 54,751	$ 90,601	$ 88,684	$ 79,185	$ 64,121	$ 286,166	$ 322,591	$ 357,249
Cost of revenues	60,685	60,577	61,157	47,703	74,367	72,805	65,049	52,361	230,123	264,583	249,032
Gross profit	18,989	16,461	13,547	7,048	16,234	15,879	14,136	11,760	56,043	58,008	108,217
Operating expenses:
Research and development	8,208	7,397	7,947	9,605	11,378	13,169	13,091	13,066	33,157	50,703	50,819
Sales and marketing	4,940	5,453	6,274	6,458	7,592	11,016	9,987	10,215	23,126	38,810	45,877
General and administrative	5,983	5,441	4,964	5,833	6,296	6,708	6,846	7,567	22,221	27,418	30,830
Restructuring and other charges	1,991	4,071	3,609	7,247	1,060	2,717	0	0	16,917	3,777	0
Total operating expenses	21,122	22,362	22,794	29,143	26,326	33,610	29,924	30,848	95,421	120,708	127,526
Loss from operations	(2,133)	(5,901)	(9,247)	(22,095)	(10,092)	(17,731)	(15,788)	(19,088)	(39,378)	(62,700)	(19,309)
Other income expense, net	(1,755)	(1,137)	(1,992)	(1,079)	(2,345)	(881)	(591)	529	(5,963)	(3,287)	(1,394)
Loss before income taxes	(3,888)	(7,038)	(11,239)	(23,174)	(12,437)	(18,612)	(16,379)	(18,559)	(45,341)	(65,987)	(20,703)
Income tax benefit (provision)	948	184	(854)	(131)	(751)	(144)	(344)	(236)	149	(1,475)	(1,379)
Net loss	$ (2,940)	$ (6,854)	$ (12,093)	$ (23,305)	$ (13,188)	$ (18,756)	$ (16,723)	$ (18,795)	$ (45,192)	$ (67,462)	$ (22,082)
Net loss per share, basic and diluted (usd per share)	$ (0.03)	$ (0.08)	$ (0.14)	$ (0.30)	$ (0.21)	$ (0.40)	$ (0.36)	$ (0.41)	$ (0.54)	$ (1.34)	$ (0.49)

SUBSEQUENT EVENTS (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended	12 Months Ended
	Feb. 28, 2018	Feb. 04, 2018	Feb. 28, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Subsequent Event [Line Items]
Proceeds from issuance of common stock				$ 26,425	$ 16,142	$ 0
Subsequent Event \| Private Placement
Subsequent Event [Line Items]
Number of shares issued (in shares)		9,523,809
Price per share issued (in USD per share)		$ 2.10
Proceeds from issuance of common stock		$ 20,000	$ 20,000
Secured Debt \| Second amendment to term loans \| Subsequent Event
Subsequent Event [Line Items]
Percent decrease in principal payments	50.00%		50.00%