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Document and Entity Information - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Feb. 26, 2016	Jun. 30, 2015
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, 2015
Amendment Flag	false
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		46.4
Entity Well-Known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 154.5

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 28,452	$ 42,032
Accounts receivable, net of allowances of $1,808 and $569 at December 31, 2015 and 2014, respectively	46,099	45,119
Inventory	40,800	21,590
Prepaid expenses and other	6,417	6,155
Total current assets	121,768	114,896
Property and equipment, net	32,118	30,824
Goodwill	3,745	3,745
Intangibles, net	2,220	1,811
Other assets	5,677	916
Total assets	165,528	152,192
Current liabilities:
Accounts payable	25,569	22,316
Accrued liabilities	19,292	26,036
Deferred revenues	3,915	2,747
Warranty obligations, current portion (includes $2,601 and $1,125 measured at fair value at December 31, 2015 and 2014, respectively)	7,072	7,607
Borrowings under revolving credit facility	17,000	0
Total current liabilities	72,848	58,706
Deferred revenues, non-current	25,115	16,612
Warranty obligations, non-current (includes $3,581 and $2,437 measured at fair value at December 31, 2015 and 2014, respectively)	23,475	26,333
Other non-current liabilities	2,641	3,589
Total liabilities	124,079	105,240
Commitments and contingencies
Stockholders’ equity:
Preferred stock, $0.00001 par value, 10,000 shares authorized; none issued and outstanding	0	0
Common stock, $0.00001 par value, 100,000 shares authorized; 45,821 and 43,756 shares issued and outstanding at December 31, 2015 and 2014, respectively	0	0
Additional paid-in capital	224,732	208,022
Accumulated deficit	(183,073)	(160,991)
Accumulated other comprehensive loss	(210)	(79)
Total stockholders’ equity	41,449	46,952
Total liabilities and stockholders’ equity	$ 165,528	$ 152,192

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Allowances, accounts receivable	$ 1,808	$ 569
Warrant obligations at fair value, current	2,601	1,125
Warrant obligations at fair value, noncurrent	$ 3,581	$ 2,437
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)	100,000,000	100,000,000
Common stock, shares issued (shares)	45,821,000	43,756,000
Common stock, shares outstanding (shares)	45,821,000	43,756,000

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Net revenues	$ 357,249	$ 343,904	$ 232,846
Cost of revenues	249,032	230,861	165,430
Gross profit	108,217	113,043	67,416
Operating expenses:
Research and development	50,819	45,386	34,524
Sales and marketing	45,877	41,003	31,080
General and administrative	30,830	31,083	23,970
Total operating expenses	127,526	117,472	89,574
Income (loss) from operations	(19,309)	(4,429)	(22,158)
Other income (expense), net:
Interest expense	(501)	(1,863)	(2,055)
Other expense	(893)	(994)	(837)
Total other expense, net	(1,394)	(2,857)	(2,892)
Income (loss) before income taxes	(20,703)	(7,286)	(25,050)
Provision for income taxes	(1,379)	(766)	(863)
Net income (loss)	$ (22,082)	$ (8,052)	$ (25,913)
Net loss per share, basic and diluted (usd per share)	$ (0.49)	$ (0.19)	$ (0.62)
Shares used in computing net loss per share, basic and diluted (shares)	44,632	42,903	41,647

Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net loss	$ (22,082)	$ (8,052)	$ (25,913)
Other comprehensive loss:
Foreign currency translation adjustments	(131)	(308)	177
Other comprehensive loss:	(131)	(308)	177
Comprehensive loss	$ (22,213)	$ (8,360)	$ (25,736)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References + Details

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Income (Loss)
BALANCE, Beginning at Dec. 31, 2012	$ 56,655	$ 0	$ 183,629	$ (127,026)	$ 52
BALANCE, Beginning (shares) at Dec. 31, 2012		40,856
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans	2,438		2,438
Issuance of common stock under employee stock plans (shares)		1,255
Stock-based compensation	6,849		6,849
Issuance of common stock upon cashless exercise of warrants	0
Issuance of common stock upon cashless exercise of warrants (shares)		12
Net loss	(25,913)			(25,913)
Foreign currency translation adjustment	177				177
BALANCE, Ending at Dec. 31, 2013	40,206	$ 0	192,916	(152,939)	229
BALANCE, Ending (shares) at Dec. 31, 2013		42,123
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock under employee stock plans	5,366		5,366
Issuance of common stock under employee stock plans (shares)		1,577
Stock-based compensation	9,740		9,740
Issuance of common stock upon cashless exercise of warrants	0
Issuance of common stock upon cashless exercise of warrants (shares)		56
Net loss	(8,052)			(8,052)
Foreign currency translation adjustment	(308)				(308)
BALANCE, Ending at Dec. 31, 2014	46,952	$ 0	208,022	(160,991)	(79)
BALANCE, Ending (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)
BALANCE, Ending at Dec. 31, 2015	$ 41,449	$ 0	$ 224,732	$ (183,073)	$ (210)
BALANCE, Ending (shares) at Dec. 31, 2015		45,821

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash flows from operating activities:
Net loss	$ (22,082)	$ (8,052)	$ (25,913)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	10,539	8,259	6,981
Provision for doubtful accounts	1,502	711	678
Net loss on disposal of assets	522	249	82
Non-cash interest expense	163	483	429
Stock-based compensation	12,696	9,740	6,849
Revaluation of contingent consideration liability	(1,827)	0	0
Deferred income tax expense (benefit)	642	(35)	(2)
Changes in operating assets and liabilities (net of acquisition):
Accounts receivable	(2,482)	(13,746)	(5,019)
Inventory	(19,210)	(5,010)	3,263
Prepaid expenses and other assets	(5,281)	(2,512)	(1,448)
Accounts payable, accrued and other liabilities	(2,620)	25,325	(1,453)
Warranty obligations	(3,393)	3,508	9,094
Deferred revenues	9,671	5,302	5,587
Net cash (used in) provided by operating activities	(21,160)	24,222	(872)
Cash flows from investing activities:
Purchases of property and equipment	(12,525)	(13,249)	(6,257)
Purchases of intangible assets	(237)	(750)	0
Acquisition of a business	0	(2,235)	0
Change in restricted cash	300	(300)	0
Net cash used in investing activities	(12,462)	(16,534)	(6,257)
Cash flows from financing activities:
Principal payments under capital leases	0	0	(40)
Proceeds from borrowings under revolving credit facility	46,000	0	0
Payments under revolving credit facility	(29,000)	0	0
Payments of deferred financing costs	(150)	0	0
Holdback payment related to prior acquisition	(300)	0	0
Repayments of term loans	0	(8,708)	(2,447)
Proceeds from issuance of common stock under employee stock plans	4,014	5,366	2,429
Net cash provided by (used in) financing activities	20,564	(3,342)	(58)
Effect of exchange rate changes on cash	(522)	(504)	83
Net (decrease) increase in cash and cash equivalents	(13,580)	3,842	(7,104)
Cash and cash equivalents — Beginning of period	42,032	38,190	45,294
Cash and cash equivalents — End of period	28,452	42,032	38,190
Supplemental disclosures of cash flow information:
Cash paid for interest	358	1,389	1,391
Cash paid for income taxes	594	472	899
Noncash financing and investing activities:
Purchases of fixed and intangible assets included in accounts payable	1,718	1,840	837
Acquisition-related contingent consideration liability	$ 0	$ 2,300	$ 0

DESCRIPTION OF BUSINESS	12 Months Ended
DESCRIPTION OF BUSINESS	Dec. 31, 2015
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. Our 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, we have shipped more than 10.3 million microinverters, representing over 2.5 gigawatts of solar PV generating capacity, and more than 430,000 Enphase residential and commercial systems have been deployed in over 100 countries.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES

12 Months Ended

Dec. 31, 2015

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.

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, and an Enlighten cloud-based monitoring service, to distributors, large installers, OEMs and strategic partners. Enlighten service revenue represented less than 2% of the total revenues for all periods presented.

Revenues from sales of microinverters and related accessories, and communication gateways are 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, (i) revenue from the sale of Envoy devices is recognized upon shipment, assuming all other revenue recognition criteria have been met and (ii) revenue from the cloud-based monitoring service is recognized ratably over the estimated economic life of the related Envoy devices of 10 years.

Deferred revenues consist of payments received from customers in advance of revenue recognition for the Company’s products and services described above. As of December 31, 2015 and 2014, 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.

Foreign Currency Forward Contracts

The Company operates and conducts business in foreign countries where its foreign entities use the local currency as their respective functional currency. As a result, the Company is exposed to movements in foreign currency exchange rates. The Company utilizes foreign currency forward contracts to reduce the impact of foreign currency fluctuations related to anticipated cash receipts from expected future revenues denominated in Euros and British Pounds as well as from intercompany transaction gains or losses. The foreign currency forward contracts are accounted for as derivatives whereby the fair value of the contracts is reported as other current assets or current liabilities in the accompanying consolidated balance sheets, and gains and losses resulting from changes in the fair value are reported in other income (expense), net, in the accompanying consolidated statements of operations.

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 $1.8 million and $0.6 million at December 31, 2015 and 2014, respectively. The following table sets forth activities in the allowance for doubtful accounts for the periods indicated:



	December 31,
	2015			2014			2013
Balance, at beginning of year	$	569		$	2,000		$	1,177
Net charges to expenses	1,502			711			678
Write-offs, net of recoveries	(263		)	(2,142		)	145
Balance, at end of year	$	1,808		$	569		$	2,000

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 did not record any significant impairments in any of the years presented.

Business Combinations

The Company allocates the fair value of purchase consideration (including contingent consideration) to the assets acquired and liabilities assumed based on their estimated fair values at the acquisition date. The excess of the fair value of purchase consideration over the fair value of these assets acquired and liabilities assumed in the acquisition is recorded as goodwill. The primary items that generate goodwill include the value of the synergies between the acquiree and the Company and the value of the acquired assembled workforce, neither of which qualifies for recognition as an intangible asset. Acquisition-related expenses are recognized separately from the business combination and are expensed as incurred. The results of operations of NPS have been included in the Company’s consolidated results prospectively from the date of acquisition. See Note 5, “Business Combination, Goodwill and Intangible Assets” to the consolidated financial statements for further discussion.

Goodwill

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.

Intangible Assets

Intangible assets include patents, customer relationships 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 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 a 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 has been 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.

If actual failure rates, claim rates, or replacement costs differ from the Company’s estimates in future periods, changes to these estimates would 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 typically offers a one year warranty for its Envoy communications gateway. The terms of the warranty do not provide the Company the right to assign its warranty obligations to a third-party. As such, the fair value option is not available and warranty obligations related to sales for Envoy communications gateway devices will continue to be accounted for on an undiscounted basis.

Research and Development Costs

The Company expenses research and development costs as incurred. Research and development costs totaled $50.8 million, $45.4 million and $34.5 million in 2015, 2014 and 2013, 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.

Contingent Consideration Liability

The estimated fair value of the contingent consideration liability, initially measured and recorded on the acquisition date, is reviewed at each reporting period and revalued to its then fair value until the contingency is resolved. Increases or decreases in the fair value of the contingent consideration liability subsequent to the acquisition date can result from changes in the assumed probabilities applied to the achievement of certain revenue targets and the corresponding payout amounts. These changes in the fair value will be recognized in the consolidated statements of operations for the period in which the estimated fair value changes.

Recently Adopted Accounting Pronouncements

In November 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” to simplify the presentation of deferred income taxes. The amendments in this update require that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. The amendments in this update apply to all entities that present a classified statement of financial position. The current requirement that deferred tax liabilities and assets of a tax-paying component of an entity be offset and presented as a single amount is not affected by the amendments in this update. The Company adopted ASU 2015-17 during the fourth quarter of 2015 and applied it retrospectively to all periods presented. The adoption of this update did not have a material impact on the consolidated balance sheets for all periods presented and had no impact on the results of operations.

Recent Accounting Pronouncements Not Yet Effective

In May 2014, the FASB issued ASU 2014-09 (Topic 606), “Revenue from Contracts with Customers,” which will replace most existing revenue recognition guidance under U.S. GAAP. The updated standard’s core principle is that revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled 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. In 2015, the FASB issued guidance to defer the effective date to fiscal years beginning after December 15, 2017 with early adoption for fiscal years beginning December 15, 2016. The guidance permits the use of either a retrospective or cumulative effect transition method. The Company has not yet selected a transition method and is currently evaluating the impact of adoption on the consolidated financial statements.

In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements—Going Concern.” The update provides U.S. GAAP guidance on management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and about related footnote disclosures. For each reporting period, management will be required to evaluate whether there are conditions or events that raise substantial doubt about a company’s ability to continue as a going concern within one year from the date the financial statements are issued. The amendments in this update are effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. The Company is currently evaluating the impact of adoption on the consolidated financial statements.

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.” ASU 2015-11 is effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. Early adoption is permitted for any interim and annual financial statements that have not yet been issued. The Company is currently evaluating the impact of adoption on the consolidated financial statements.

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 is currently evaluating the impact of adoption on our 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.

INVENTORY

12 Months Ended

Dec. 31, 2015

Inventory Disclosure [Abstract]

INVENTORY

Inventory as of December 31, 2015 and 2014, consists of the following (in thousands):



	December 31,
	2015		2014
Raw materials	$	2,202	$	3,429
Finished goods	38,598		18,161
Total inventory	$	40,800	$	21,590

PROPERTY AND EQUIPMENT, NET

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

PROPERTY AND EQUIPMENT, NET

As of December 31, 2015 and 2014, property and equipment consists of the following (in thousands):



	Estimated Useful Life (Years)	December 31,
	Estimated Useful Life (Years)	2015			2014
Equipment and machinery	5	$	34,694		$	28,923
Furniture and fixtures	5–7	3,556			3,032
Computer equipment	3–5	2,699			2,194
Capitalized software costs	3–5	11,041			8,905
Leasehold improvements	4–10	8,643			6,636
Construction in process		2,994			4,911
Total		63,627			54,601
Less accumulated depreciation and amortization		(31,509		)	(23,777		)
Property and equipment, net		$	32,118		$	30,824

Depreciation and amortization expense for property and equipment was $10.0 million, $8.1 million and $7.0 million, in 2015, 2014 and 2013, respectively.

As of December 31, 2015 and 2014, unamortized capitalized software costs were $3.3 million.

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS

12 Months Ended

Dec. 31, 2015

Business Combinations [Abstract]

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS

Acquisition

On December 12, 2014, the Company acquired substantially all of the assets of Next Phase Solar, Inc. (“NPS”). Founded in 2009 and based in Berkeley, California, NPS is a provider of services designed specifically for the solar industry. The acquisition complemented the Company’s then existing asset management and operations and maintenance service offering.

The following table summarizes the allocation of the total purchase price to acquired tangible and identifiable intangible assets based on their estimated fair values as of the date of acquisition (in thousands):



Cash consideration	$	2,535
Contingent consideration	2,300
Total purchase consideration	$	4,835

Property and equipment	$	190
Customer relationships	900
Goodwill	3,745
Net assets acquired	$	4,835

This acquisition has been accounted for as a business combination. The total purchase consideration of $4.8 million consisted of $2.5 million in cash (of which $0.3 million was held back for potential breaches of representations and warranties) and $2.3 million of contingent consideration (described below). The indemnity holdback was released in 2015 and has been reflected as a cash outflow from financing activities in the statement of cash flows

The fair values assigned to the net assets acquired are based on management’s estimates and assumptions. The goodwill of $3.7 million is attributable to the value of the synergies expected to arise upon the integration of NPS into the Company’s operations and the value of the acquired workforce. A portion of goodwill related to this acquisition is deductible for income tax purposes.

The fair value of the acquired customer relationships was calculated by discounting the projected discrete after-tax cash flows from these existing customers (less an anticipated customer attrition rate) to its present value.

The purchase consideration includes a contingent consideration arrangement that requires additional cash payments by the Company based on certain defined 2015 and 2016 revenue targets. Amounts are payable in early 2016 and 2017. The range of the undiscounted amounts the Company could pay under the contingent consideration arrangement is between zero and $5.5 million. The fair value of the contingent consideration was estimated based on significant inputs not observed in the market and thus represents a Level 3 input as defined in connection with the fair value hierarchy. See Note 8, “Fair Value Measurements” for further discussion. Any future change in the estimated fair value of the contingent consideration will be recognized in the consolidated statements of operations for the period in which the estimated fair value changes. Amounts earned for achieving 2015 revenue targets were not material. As of December 31, 2015, the estimated fair value of contingent consideration relates to achieving 2016 revenue targets (see Note 8).

The acquisition was not material to the Company’s financial position or results of operations, and therefore proforma operating results for NPS have not been presented. The results of operations of NPS have been included in the Company’s consolidated results prospectively from the date of acquisition. The Company recognized approximately $0.2 million of acquisition related costs in 2014, which were recorded in general and administrative expenses in the Company’s consolidated statements of operations.

Goodwill and Intangible Assets



	December 31, 2015							December 31, 2014
	Gross		Accumulated Amortization			Net		Gross		Accumulated Amortization			Net
Goodwill	$	3,745	$	—		$	3,745	$	3,745	$	—		$	3,745

Other indefinite-lived intangibles	$	286	$	—		$	286	$	286	$	—		$	286
Intangibles assets with finite lives:
Customer relationships	900		(180		)	720		900		—			900
Patents and licensed technology	1,665		(451		)	1,214		750		(125		)	625
Total purchased intangibles	$	2,851	$	(631	)	$	2,220	$	1,936	$	(125	)	$	1,811

In July 2014, the Company purchased certain patents related to system interconnection and photovoltaic AC module construction. The patents are being amortized over their legal life of 3 years. The customer relationship intangible resulted from the Company’s NPS acquisition and is being amortized on a straight-line basis over its estimated useful life of 5 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 $0.5 million and $0.1 million for the years ended December 31, 2015 and 2014, respectively. As of December 31, 2015, estimated future amortization expense related to finite-lived intangible assets was as follows:



Year	(In thousands)
2016	$	735
2017	610
2018	409
2019	180
Total	$	1,934

ACCRUED LIABILITIES

12 Months Ended

Dec. 31, 2015

Payables and Accruals [Abstract]

ACCRUED LIABILITIES

Accrued liabilities consisted of the following (in thousands):



	December 31,
	2015		2014
Salaries, commissions, incentive compensation and benefits	$	5,402	$	14,871
Customer rebates and sales incentives	8,274		5,083
Freight	3,063		1,917
Other	2,553		4,165
Total	19,292		26,036

WARRANTY OBLIGATIONS

12 Months Ended

Dec. 31, 2015

Product Warranties Disclosures [Abstract]

WARRANTY OBLIGATIONS

The Company’s warranty activities during 2015, 2014 and 2013 were as follows (in thousands):



	December 31,
	2015			2014			2013
Balance, at beginning of year	$	33,940		30,432			$	21,338
Accruals for warranties issued during the year	4,383			4,309			6,303
Changes in estimates	31			8,391			10,303
Settlements	(7,269		)	(8,793		)	(7,512		)
Increase due to accretion expense	1,001			195			—
Fair value adjustments	(1,539		)	(594		)	—
Balance, at end of year	30,547			33,940			30,432
Less current portion	(7,072		)	(7,607		)	(4,942		)
Long-term portion	$	23,475		$	26,333		$	25,490

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 5.4 million fourth generation microinverters since mid-2013 and continues to sell the fourth generation microinverters. In the fourth quarter of 2015, the Company started selling its fifth generation microinverters.

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:

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.

2014

In 2014, primarily in the second and fourth quarters, the Company experienced actual failures of its second generation microinverters that exceeded its then current failure rate estimate. Based on continuing analysis of field performance data and diagnostic root-cause failure analysis performed on returned units, the Company concluded that it was necessary to increase the estimated failure rates for its second generation product and recorded additional warranty expense $8.6 million in 2014. In addition, net changes in estimates related to replacement costs reduced warranty expense for all product generations by $0.2 million and were comprised of increased estimates of certain labor reimbursement costs expected to be paid to third party installers performing replacement services for its second generation product of $1.3 million, offset by a $1.5 million decrease to estimated costs of replacement microinverter units for all product generations.

2013

In 2013, primarily in the second, third and fourth quarters, the Company experienced actual failures of its second generation microinverters that exceeded its then current failure rate estimate. Based on continuing analysis of field performance data and diagnostic root-cause failure analysis performed on returned units, the Company concluded that it was necessary to increase the estimated failure rates for its second generation product and recorded additional warranty expense of $19.5 million in 2013. During the third quarter of 2013, the Company recorded a reduction to warranty expense of $3.1 million related to a decrease in the expected failure rate of the Company’s third generation product. The Company concluded that there was sufficient historical data of actual field performance of previously sold third generation products to support a lower estimated failure rate.

In addition, the Company updated its estimated claim rates for its second and third generation products resulting in a decrease to warranty expense of $4.2 million. The revision to estimated claim rates was based on the Company’s observed historical end user behavior and assumptions with respect to expected customer behavior over the 15 or 25 year warranty term.

Also, the Company decreased warranty expense by $1.9 million primarily to reflect estimated lower costs to produce fourth generation microinverters to fulfill warranty obligations for second and third generation microinverters.

FAIR VALUE MEASUREMENTS

12 Months Ended

Dec. 31, 2015

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 assets and liabilities that were measured at fair value on a recurring basis and its categorization within the fair value hierarchy at December 31, 2015 and 2014 (in thousands):



	Fair Value Hierarchy	December 31, 2015		December 31, 2014
Assets:
Foreign currency forward contracts	Level 2	$	86	$	76

Liabilities:
Foreign currency forward contracts	Level 2	$	9	$	—
Warranty obligations	Level 3	6,182		3,562
Contingent consideration	Level 3	473		2,300

Foreign Currency Forward Contracts

The Company utilizes foreign currency forward contracts from time to time to reduce the impact of foreign currency fluctuations arising from both sales and purchases denominated in Euros and the British Pound Sterling.

As of December 31, 2015 and 2014, the aggregate gross notional amounts of outstanding foreign currency forward contracts, all with maturities of less than one year, were $2.4 million and $1.5 million, respectively.

The Company recorded $0.3 million and $0.3 million of net gains in 2015 and 2014, respectively, and $0.4 million of net losses in 2013 related to foreign currency forward contracts.

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, 2013	$	—
Accruals for warranties issued during period	3,989
Changes in estimates	26
Settlements	(54		)
Increase due to accretion expense	195
Fair value adjustments	(594		)
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

Contingent Consideration

The fair value of the contingent consideration recognized on the acquisition date of $2.3 million was estimated by applying the income approach. That measure is based on significant Level 3 inputs not observable in the market. Key assumptions include (1) probability adjusted level of revenues between $2.6 million and $17.0 million and the resultant payout; and (2) a risk-adjusted discount rate was estimated using a capital asset pricing model, which reflects an expected rate of return required by a market participant holding a similarly risky asset.

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



Balance—December 31, 2014	$	2,300
Fair value adjustment to contingent consideration	(1,827		)
Balance—December 31, 2015	$	473

The decrease in fair value of contingent consideration was due to amounts earned for achieving 2015 revenue targets was lower than originally forecasted and revisions to sales projections related to achieving 2016 revenue targets.

Quantitative and Qualitative Information about Level 3 Fair Value Measurements

As of December 31, 2015, 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	25%

Contingent consideration	Probability-weighted discounted cash flows	Risk-adjusted discount rate	17%

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 ($162,000) $173,000 (decrease) increase, respectively, to the fair value measurement of the liability.

Contingent Consideration

Changes in assumed probability adjustments with respect to achievement of target metric can materially impact the fair value measurement of contingent consideration as of the acquisition date and for each subsequent period. Assumptions about the probability and amount of payout will require less subjectivity over the course of the earnout period as management refines estimates based on actual events. Due to the short duration of the remaining earnout period of one year, increasing (decreasing) the risk-adjusted discount rate by 100 basis points would not have a material impact on the fair value measurement of contingent consideration.

REVOLVING CREDIT FACILITY	12 Months Ended
REVOLVING CREDIT FACILITY	Dec. 31, 2015
Debt Disclosure [Abstract]
REVOLVING CREDIT FACILITY	REVOLVING CREDIT FACILITY The Company maintains a $50.0 million revolving credit facility with Wells Fargo Bank, N.A. (“Wells Fargo”) that was entered into on November 7, 2012, as first amended on February 14, 2014. On December 18, 2015, the Company entered into an amended and restated revolving credit agreement (the “Revolver”) which extended the maturity date from November 7, 2016 to November 7, 2019 and added an uncommitted accordion feature that could increase the size of the facility by $25.0 million, subject to certain approvals and meeting certain criteria. Availability under the Revolver is subject to a borrowing base calculation that limits availability to a percentage of eligible domestic accounts receivable plus a percentage of the value of eligible domestic inventory, less certain reserves. Borrowings under the Revolver bear interest in cash at an annual rate equal to, at the Company’s option, either LIBOR or a “base rate” that is comprised of, among other things, the prime rate, plus a margin that is between 1.0% and 3.75% depending on the currency borrowed and the specific term of repayment. The Revolver requires the Company to pay a commitment fee between 0.25% and 0.375% based on the average daily unused portion of the revolving credit commitment. The Revolver is secured by a pledge of substantially all assets of the Company other than intellectual property and contains customary affirmative and negative covenants (including restrictions on the Company’s ability to make dividend payments) and events of default. In addition, the Revolver requires the Company to maintain at least $15.0 million of liquidity at all times, of which at least $5.0 million must be undrawn availability. As of December 31, 2015, the Company was in compliance with such covenants under the Revolver. As of December 31, 2015, the amount outstanding under the Revolver was $17.0 million leaving an unused borrowing capacity of $27.7 million. The weighted-average interest rate related to these borrowings was 4.3%. No amounts were outstanding under the Revolver at December 31, 2014.

COMMITMENTS AND CONTINGENCIES

12 Months Ended

Dec. 31, 2015

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 2015, 2014 and 2013 was $3.2 million, $2.6 million and $2.4 million, respectively.

The Company’s minimum lease payments under noncancelable operating leases, exclusive of executory costs, as of December 31, 2015 are as follows (in thousands):



2016	$	2,618
2017	2,711
2018	2,700
2019	2,739
2020	2,577
Thereafter	4,789
Total minimum lease payments	$	18,134

Purchase Obligations—The Company has contractual obligations related to component inventory that our primary contract manufacturer procures on our behalf in accordance with our production forecast and a take-or-pay supply agreement for the purchase of silicone encapsulates that expires on December 31, 2018. As of December 31, 2015, these purchase obligations totaled approximately $51.0 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.

STOCK-BASED COMPENSATION

12 Months Ended

Dec. 31, 2015

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, 2015, there were 3.5 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 may, 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 will automatically increase, 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, 2015, 1,035,944 shares of common stock remained available for issuance pursuant to future grants under the 2011 Plan. On January 1, 2016, the shares authorized for issuance under the 2011 Plan automatically increased by 2,061,949 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 initially authorizes 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 330,396 shares of the Company’s common stock or a lesser number of shares of common stock 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 1 and November 1 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, 2015, there were 366,432 shares of the Company’s common stock available for issuance under the ESPP. On January 1, 2016, the shares authorized for issuance under the ESPP automatically increased by 330,396 shares.

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 stock price volatility for option awards granted prior to March 31, 2014 was determined based on an average of the historical volatilities of the common stock of several peer companies with characteristics similar to those of the Company. For option awards granted after March 31, 2014, the Company used a blended volatility estimate consisting of its own historical share price volatility (as the Company had at least two years of historical stock price data) augmented with historical volatility of peer companies for periods preceding the Company’s initial public offering such that the time period over which historical volatility data used was at least equal to the expected term of the option award.


•	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,
	2015			2014			2013
Expected term (in years)	4.5			4.5			4.4
Expected volatility	72.5		%	67.7		%	68.4		%
Annual risk-free rate of return	1.4		%	1.4		%	1.0		%
Dividend yield	—		%	—		%	—		%
Weighted-average fair value on grant date	$	4.68		$	5.64		$	3.84

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,
	2015		2014		2013
Cost of revenues	$	1,217	$	816	$	438
Research and development	4,559		3,127		2,110
Sales and marketing	3,162		2,487		1,812
General and administrative	3,758		3,310		2,489
Total stock-based compensation expense	$	12,696	$	9,740	$	6,849

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,
	2015		2014		2013
Stock options and restricted stock units	$	10,685	$	8,845	$	6,314
ESPP	2,011		895		535
Total stock-based compensation expense	$	12,696	9,740		$	6,849

As of December 31, 2015, there was approximately $18.6 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 2.5 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, 2012	8,169		$	3.28
Granted	1,506		7.17
Exercised	(822	)	1.69
Canceled	(344	)	7.74
Options outstanding — December 31, 2013	8,509		3.94
Granted	1,311		10.36
Exercised	(886	)	4.33
Canceled	(302	)	7.58
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

The following table summarizes information about stock options outstanding at December 31, 2015:



	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 —– $1.63	2,995	3.9	$	0.94	2,995	$	0.94
$1.88 —– $6.90	1,853	5.1	5.14		1,095	5.51
$6.98 —– $8.57	1,667	4.9	7.81		1,203	7.84
$8.58 —– $15.15	1,525	5.7	10.72		658	10.34
$16.01 —– $16.01	130	5.3	16.01		50	16.01
Total	8,170	4.7	5.36		6,001	4.31

The intrinsic value of options exercised in 2015, 2014 and 2013 was $4.9 million, $5.5 million and $3.2 million, respectively. As of December 31, 2015, there were 8.0 million options outstanding that were vested and expected to vest. Such options have a weighted-average exercise price of $5.31 and a weighted-average remaining contractual term of 4.7 years. As of December 31, 2015, the aggregate intrinsic value was $7.8 million for the 6.0 million exercisable shares. The intrinsic value is based on the Company’s common stock fair value of $3.51 per share as of December 31, 2015.

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, 2012	248		$	5.53
Granted	285		6.92
Vested	(107	)	6.08
Canceled	(8	)	7.07
Outstanding at December 31, 2013	418		6.31
Granted	1,250		8.68
Vested	(281	)	7.38
Canceled	(42	)	7.56
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

The intrinsic value of restricted stock units vested during 2015, 2014 and 2013 was $4.2 million, $3.2 million and $0.8, respectively. As of December 31, 2015, the restricted stock units outstanding had a weighted average remaining contractual term of 1.4 years with an intrinsic value of $4.6 million.

ESPP

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



	Years Ended December 31,
	2015		2014		2013
Proceeds from common stock issued under ESPP	$	2,497	$	1,531	$	1,047
Shares of common stock issued	499		410		327
Weighted-average price per share	$	5.00	$	3.73	$	3.20

INCOME TAXES

12 Months Ended

Dec. 31, 2015

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,
	2015			2014			2013
United States	$	(22,120	)	$	(8,732	)	$	(26,118	)
Foreign	1,417			1,446			1,068
Total	$	(20,703	)	$	(7,286	)	$	(25,050	)

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



	Year Ended December 31,
	2015			2014			2013
Current:
Federal	$	—		$	—		$	—
State	44			85			—
Foreign	693			716			865
	737			801			865
Deferred:
Federal	652			—			—
State	41			—			—
Foreign	(51		)	(35		)	(2		)
	642			(35		)	(2		)
Provision for income taxes	$	1,379		$	766		$	863

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):



	Year Ended December 31,
	2015			2014			2013
Income tax benefit at statutory federal rate	$	(7,039	)	$	(2,477	)	$	(8,517	)
State taxes, net of federal benefit	56			(4,576		)	(883		)
Change in valuation allowance	7,812			16,646			8,353
Foreign tax rate and tax law differential	(29		)	(43		)	237
Tax credits	(1,553		)	(5,619		)	—
Stock-based compensation	1,932			957			1,191
Other permanent items	61			231			220
Other nondeductible/nontaxable items	(72		)	(4,586		)	(2		)
Uncertain tax positions	211			233			264
Provision for income taxes	$	1,379		$	766		$	863

A summary of significant components of the Company’s deferred tax assets and liabilities as of December 31, 2015 and 2014 is as follows (in thousands):



	December 31,
	2015			2014
Deferred tax assets:
Allowances and reserves	$	14,639		$	18,771
Net operating loss and tax credit carryforwards	46,812			28,511
Stock-based compensation	3,055			2,154
Deferred revenue	5,966			3,843
Fixed assets and intangibles	6,830			9,163
Other	3,327			2,023
Subtotal	80,629			64,465
Less valuation allowance	(80,529		)	(64,428		)
Total deferred tax assets, net of valuation allowance	100			37
Deferred tax liabilities:
Goodwill	(693		)	—
Total deferred tax liabilities	(693		)	—
Net deferred tax asset/(liability)	$	(593	)	$	37

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, 2015. Therefore, the Company has recorded a full valuation allowance on its U.S. and state deferred tax assets at December 31, 2015. 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.

The Company considers the earnings of certain non-U.S. subsidiaries to be indefinitely invested outside the United States on the basis of estimates that future domestic cash generation will be sufficient to meet future domestic cash needs and the Company’s specific plans for reinvestment of those subsidiary earnings. Accordingly, the Company has not recorded a deferred tax liability related to the U.S. federal and state income taxes and foreign withholding taxes on approximately $3.5 million of undistributed earnings of foreign subsidiaries indefinitely invested outside the United States. If such earnings were repatriated, additional tax provisions may result.

The Company has net operating loss carryforwards for federal and California income tax purposes of approximately $83.2 million and $78.3 million, respectively, as of December 31, 2015. The federal and state net operating loss carryforwards, if not utilized, will expire beginning in 2026 and 2016, respectively. Utilization of the net operating loss carryforwards may be subject to a substantial annual limitation due to the ownership change limitations provided by the Internal Revenue Code of 1986, as amended (the “Code”), and similar state provisions. The annual limitation may result in the expiration of net operating losses before utilization. The Company has completed a study to assess whether an ownership change has occurred or whether there have been multiple ownership changes since the Company became a loss corporation under the Code. However, the Company does not anticipate these limitations will significantly impact its ability to utilize the net operating losses and tax credit carryforwards.

The Company has approximately $7.2 million of federal research credit and $7.1 million of state research credit carryforwards. The federal credits begin to expire in 2026 and the state credits can be carried forward indefinitely.

As a result of certain realization requirements under income tax accounting for stock-based compensation, the table of deferred tax assets and liabilities shown above does not include certain deferred tax assets as of December 31, 2015 and 2014 that arose directly from tax deductions related to equity compensation greater than compensation recognized for financial reporting. Equity will be increased by $6.0 million if and when such deferred tax assets are ultimately realized.

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. There were no significant unrecognized tax benefits recorded upon adoption and the increase to the unrecognized tax benefits in 2015 was $1.1 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,
	2015			2014		2013
Unrecognized tax benefits—at beginning of year	$	4,426		$	376	$	160
Increases in balances related to tax positions taken in prior years	14			1,895		79
Increases in balances related to tax positions taken in current year	1,053			2,155		137
Lapses in statutes of limitations	(11		)	—		—
Unrecognized tax benefits—at end of year	$	5,482		$	4,426	$	376

The Company’s tax returns continue to remain subject to examination by U.S. federal authorities for the years 2006 through 2015 and by California state authorities for the years 2006 through 2015 due to the use of net operating losses generated in tax years prior to the statutory three-year limit.

CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS	12 Months Ended
CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS	Dec. 31, 2015
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, 2015, amounts due from one customer represented 15% of the total accounts receivable balance. As of December 31, 2014, the Company’s two largest accounts receivable balances represented 15% and 11% of the total accounts receivable balance. In 2015, two customers accounted for 17% and 12% of total net revenues. In 2014, two customers accounted for 24% and 16% of total net revenues. In 2013, three customers accounted for 15%, 14% and 11% of total net revenues.

NET LOSS PER SHARE

12 Months Ended

Dec. 31, 2015

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,
	2015	2014	2013
Stock options to purchase common stock	8,646	8,502	8,196
Unvested restricted stock units	1,506	1,258	381
Warrants to purchase common stock	111	195	308
Total	10,263	9,955	8,885

SEGMENT AND GEOGRAPHIC INFORMATION

12 Months Ended

Dec. 31, 2015

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,
	2015		2014		2013
United States	$	303,195	$	294,549	$	192,881
International	54,054		49,355		39,965
Total	$	357,249	$	343,904	$	232,846

Long-Lived Assets



	As of December 31,
	2015		2014		2013
United States	$	21,913	$	20,037	$	16,262
China	7,950		9,585		7,130
Other	2,255		1,202		1,461
Total	$	32,118	$	30,824	$	24,853

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 7: http://www.xbrl.org/2003/role/presentationRef
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-SubTopic 10
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-Name Accounting Standards Codification
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Reference 14: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

Quarterly Financial Information (Unaudited)

12 Months Ended

Dec. 31, 2015

Quarterly Financial Information Disclosure [Abstract]

Quarterly Financial Information (unaudited)

Quarterly Financial Information (Unaudited)

The following tables show a summary of the Company’s quarterly financial information for each of the four quarters of 2015 and 2014 (in thousands, except per share data):



	Years Ended December 31, 2015
	March 31			June 30			September 30			December 31

Net revenues	$	86,653		$	102,093		$	102,874		$	65,629
Cost of revenues	58,629			69,066			71,408			49,929
Gross profit	28,024			33,027			31,466			15,700
Operating expenses:
Research and development	13,430			12,786			12,059			12,544
Sales and marketing	11,937			12,508			10,510			10,922
General and administrative	8,205			8,102			7,118			7,405
Total operating expenses	33,572			33,396			29,687			30,871
Income (loss) from operations	(5,548		)	(369		)	1,779			(15,171		)
Other expense, net	(605		)	(8		)	(844		)	63
Income (loss) before income taxes	(6,153		)	(377		)	935			(15,108		)
Provision for income taxes	(167		)	(226		)	(311		)	(675		)
Net income (loss)	$	(6,320	)	$	(603	)	$	624		$	(15,783	)
Net income (loss) per share, basic	$	(0.14	)	$	(0.01	)	$	0.01		$	(0.35	)
Net income (loss) per share, diluted	$	(0.14	)	$	(0.01	)	$	0.01		$	(0.35	)

	Years Ended December 31, 2014
	March 31			June 30			September 30			December 31
Net revenues	$	57,580		$	82,004		$	99,113		$	105,207
Cost of revenues	38,925			55,172			66,592			70,172
Gross profit	18,655			26,832			32,521			35,035
Operating expenses:
Research and development	9,086			11,148			12,112			13,040
Sales and marketing	8,828			10,493			9,884			11,798
General and administrative	6,526			7,679			8,632			8,246
Total operating expenses	24,440			29,320			30,628			33,084
Income (loss) from operations	(5,785		)	(2,488		)	1,893			1,951
Other expense, net	(342		)	(428		)	(953		)	(1,134		)
Income (loss) before income taxes	(6,127		)	(2,916		)	940			817
Provision for income taxes	(109		)	(115		)	(127		)	(415		)
Net income (loss)	$	(6,236	)	$	(3,031	)	$	813		$	402
Net income (loss) per share, basic	$	(0.15	)	$	(0.07	)	$	0.02		$	0.01
Net income (loss) per share, diluted	$	(0.15	)	$	(0.07	)	$	0.02		$	0.01

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	12 Months Ended
SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	Dec. 31, 2015
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.
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, and an Enlighten cloud-based monitoring service, to distributors, large installers, OEMs and strategic partners. Enlighten service revenue represented less than 2% of the total revenues for all periods presented. Revenues from sales of microinverters and related accessories, and communication gateways are 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, (i) revenue from the sale of Envoy devices is recognized upon shipment, assuming all other revenue recognition criteria have been met and (ii) revenue from the cloud-based monitoring service is recognized ratably over the estimated economic life of the related Envoy devices of 10 years. Deferred revenues consist of payments received from customers in advance of revenue recognition for the Company’s products and services described above.
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.
Foreign Currency Forward Contracts	Foreign Currency Forward Contracts The Company operates and conducts business in foreign countries where its foreign entities use the local currency as their respective functional currency. As a result, the Company is exposed to movements in foreign currency exchange rates. The Company utilizes foreign currency forward contracts to reduce the impact of foreign currency fluctuations related to anticipated cash receipts from expected future revenues denominated in Euros and British Pounds as well as from intercompany transaction gains or losses. The foreign currency forward contracts are accounted for as derivatives whereby the fair value of the contracts is reported as other current assets or current liabilities in the accompanying consolidated balance sheets, and gains and losses resulting from changes in the fair value are reported in other income (expense), net, in the accompanying consolidated statements of operations.
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.
Business Combinations	Business Combinations The Company allocates the fair value of purchase consideration (including contingent consideration) to the assets acquired and liabilities assumed based on their estimated fair values at the acquisition date. The excess of the fair value of purchase consideration over the fair value of these assets acquired and liabilities assumed in the acquisition is recorded as goodwill. The primary items that generate goodwill include the value of the synergies between the acquiree and the Company and the value of the acquired assembled workforce, neither of which qualifies for recognition as an intangible asset. Acquisition-related expenses are recognized separately from the business combination and are expensed as incurred. The results of operations of NPS have been included in the Company’s consolidated results prospectively from the date of acquisition.
Goodwill and Intangible Assets	Goodwill 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. Intangible Assets Intangible assets include patents, customer relationships 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 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 a 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.
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. If actual failure rates, claim rates, or replacement costs differ from the Company’s estimates in future periods, changes to these estimates would 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 typically offers a one year warranty for its Envoy communications gateway. The terms of the warranty do not provide the Company the right to assign its warranty obligations to a third-party. As such, the fair value option is not available and warranty obligations related to sales for Envoy communications gateway devices will continue to be accounted for on an undiscounted basis.
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.
Contingent Consideration Liability	Contingent Consideration Liability The estimated fair value of the contingent consideration liability, initially measured and recorded on the acquisition date, is reviewed at each reporting period and revalued to its then fair value until the contingency is resolved. Increases or decreases in the fair value of the contingent consideration liability subsequent to the acquisition date can result from changes in the assumed probabilities applied to the achievement of certain revenue targets and the corresponding payout amounts. These changes in the fair value will be recognized in the consolidated statements of operations for the period in which the estimated fair value changes.
Recently Adopted Accounting Pronouncements and Recent Accounting Pronouncements Not Yet Effective	Recently Adopted Accounting Pronouncements In November 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” to simplify the presentation of deferred income taxes. The amendments in this update require that deferred tax liabilities and assets be classified as noncurrent in a classified statement of financial position. The amendments in this update apply to all entities that present a classified statement of financial position. The current requirement that deferred tax liabilities and assets of a tax-paying component of an entity be offset and presented as a single amount is not affected by the amendments in this update. The Company adopted ASU 2015-17 during the fourth quarter of 2015 and applied it retrospectively to all periods presented. The adoption of this update did not have a material impact on the consolidated balance sheets for all periods presented and had no impact on the results of operations. Recent Accounting Pronouncements Not Yet Effective In May 2014, the FASB issued ASU 2014-09 (Topic 606), “Revenue from Contracts with Customers,” which will replace most existing revenue recognition guidance under U.S. GAAP. The updated standard’s core principle is that revenue is recognized when promised goods or services are transferred to customers in an amount that reflects the consideration to which an entity expects to be entitled 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. In 2015, the FASB issued guidance to defer the effective date to fiscal years beginning after December 15, 2017 with early adoption for fiscal years beginning December 15, 2016. The guidance permits the use of either a retrospective or cumulative effect transition method. The Company has not yet selected a transition method and is currently evaluating the impact of adoption on the consolidated financial statements. In August 2014, the FASB issued ASU 2014-15, “Presentation of Financial Statements—Going Concern.” The update provides U.S. GAAP guidance on management’s responsibility in evaluating whether there is substantial doubt about a company’s ability to continue as a going concern and about related footnote disclosures. For each reporting period, management will be required to evaluate whether there are conditions or events that raise substantial doubt about a company’s ability to continue as a going concern within one year from the date the financial statements are issued. The amendments in this update are effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. The Company is currently evaluating the impact of adoption on the consolidated financial statements. 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.” ASU 2015-11 is effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years. Early adoption is permitted for any interim and annual financial statements that have not yet been issued. The Company is currently evaluating the impact of adoption on the consolidated financial statements. 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 is currently evaluating the impact of adoption on our 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.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)

12 Months Ended

Dec. 31, 2015

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:



	December 31,
	2015			2014			2013
Balance, at beginning of year	$	569		$	2,000		$	1,177
Net charges to expenses	1,502			711			678
Write-offs, net of recoveries	(263		)	(2,142		)	145
Balance, at end of year	$	1,808		$	569		$	2,000

INVENTORY (Tables)

12 Months Ended

Dec. 31, 2015

Inventory Disclosure [Abstract]

Summary of Inventory

Inventory as of December 31, 2015 and 2014, consists of the following (in thousands):



	December 31,
	2015		2014
Raw materials	$	2,202	$	3,429
Finished goods	38,598		18,161
Total inventory	$	40,800	$	21,590

PROPERTY AND EQUIPMENT, NET (Tables)

12 Months Ended

Dec. 31, 2015

Property, Plant and Equipment [Abstract]

Summary of Property and Equipment

As of December 31, 2015 and 2014, property and equipment consists of the following (in thousands):



	Estimated Useful Life (Years)	December 31,
	Estimated Useful Life (Years)	2015			2014
Equipment and machinery	5	$	34,694		$	28,923
Furniture and fixtures	5–7	3,556			3,032
Computer equipment	3–5	2,699			2,194
Capitalized software costs	3–5	11,041			8,905
Leasehold improvements	4–10	8,643			6,636
Construction in process		2,994			4,911
Total		63,627			54,601
Less accumulated depreciation and amortization		(31,509		)	(23,777		)
Property and equipment, net		$	32,118		$	30,824

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS (Tables)

12 Months Ended

Dec. 31, 2015

Business Combinations [Abstract]

Summary of Allocated Purchase Price to Acquired Tangible and Identifiable Intangible Assets Based on Estimated Fair Value



Cash consideration	$	2,535
Contingent consideration	2,300
Total purchase consideration	$	4,835

Property and equipment	$	190
Customer relationships	900
Goodwill	3,745
Net assets acquired	$	4,835

Summary of Goodwill and Purchased Intangible Assets



	December 31, 2015							December 31, 2014
	Gross		Accumulated Amortization			Net		Gross		Accumulated Amortization			Net
Goodwill	$	3,745	$	—		$	3,745	$	3,745	$	—		$	3,745

Other indefinite-lived intangibles	$	286	$	—		$	286	$	286	$	—		$	286
Intangibles assets with finite lives:
Customer relationships	900		(180		)	720		900		—			900
Patents and licensed technology	1,665		(451		)	1,214		750		(125		)	625
Total purchased intangibles	$	2,851	$	(631	)	$	2,220	$	1,936	$	(125	)	$	1,811

Schedule of Estimated Future Amortization Expense Related to Finite-lived Intangible Assets

As of December 31, 2015, estimated future amortization expense related to finite-lived intangible assets was as follows:



Year	(In thousands)
2016	$	735
2017	610
2018	409
2019	180
Total	$	1,934

ACCRUED LIABILITIES (Tables)

12 Months Ended

Dec. 31, 2015

Payables and Accruals [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities consisted of the following (in thousands):



	December 31,
	2015		2014
Salaries, commissions, incentive compensation and benefits	$	5,402	$	14,871
Customer rebates and sales incentives	8,274		5,083
Freight	3,063		1,917
Other	2,553		4,165
Total	19,292		26,036

WARRANTY OBLIGATIONS (Tables)

12 Months Ended

Dec. 31, 2015

Product Warranties Disclosures [Abstract]

Summary of Warranty Activity

The Company’s warranty activities during 2015, 2014 and 2013 were as follows (in thousands):



	December 31,
	2015			2014			2013
Balance, at beginning of year	$	33,940		30,432			$	21,338
Accruals for warranties issued during the year	4,383			4,309			6,303
Changes in estimates	31			8,391			10,303
Settlements	(7,269		)	(8,793		)	(7,512		)
Increase due to accretion expense	1,001			195			—
Fair value adjustments	(1,539		)	(594		)	—
Balance, at end of year	30,547			33,940			30,432
Less current portion	(7,072		)	(7,607		)	(4,942		)
Long-term portion	$	23,475		$	26,333		$	25,490

FAIR VALUE MEASUREMENTS (Tables)

12 Months Ended

Dec. 31, 2015

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



	Fair Value Hierarchy	December 31, 2015		December 31, 2014
Assets:
Foreign currency forward contracts	Level 2	$	86	$	76

Liabilities:
Foreign currency forward contracts	Level 2	$	9	$	—
Warranty obligations	Level 3	6,182		3,562
Contingent consideration	Level 3	473		2,300

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

As of December 31, 2015, 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	25%

Contingent consideration	Probability-weighted discounted cash flows	Risk-adjusted discount rate	17%

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, 2013	$	—
Accruals for warranties issued during period	3,989
Changes in estimates	26
Settlements	(54		)
Increase due to accretion expense	195
Fair value adjustments	(594		)
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

Contingent consideration

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 contingent consideration measured at fair value for the periods indicated (in thousands):



Balance—December 31, 2014	$	2,300
Fair value adjustment to contingent consideration	(1,827		)
Balance—December 31, 2015	$	473

COMMITMENTS AND CONTINGENCIES (Tables)

12 Months Ended

Dec. 31, 2015

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, 2015 are as follows (in thousands):



2016	$	2,618
2017	2,711
2018	2,700
2019	2,739
2020	2,577
Thereafter	4,789
Total minimum lease payments	$	18,134

STOCK-BASED COMPENSATION (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015			2014			2013
Expected term (in years)	4.5			4.5			4.4
Expected volatility	72.5		%	67.7		%	68.4		%
Annual risk-free rate of return	1.4		%	1.4		%	1.0		%
Dividend yield	—		%	—		%	—		%
Weighted-average fair value on grant date	$	4.68		$	5.64		$	3.84

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,
	2015		2014		2013
Cost of revenues	$	1,217	$	816	$	438
Research and development	4,559		3,127		2,110
Sales and marketing	3,162		2,487		1,812
General and administrative	3,758		3,310		2,489
Total stock-based compensation expense	$	12,696	$	9,740	$	6,849

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,
	2015		2014		2013
Stock options and restricted stock units	$	10,685	$	8,845	$	6,314
ESPP	2,011		895		535
Total stock-based compensation expense	$	12,696	9,740		$	6,849

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, 2012	8,169		$	3.28
Granted	1,506		7.17
Exercised	(822	)	1.69
Canceled	(344	)	7.74
Options outstanding — December 31, 2013	8,509		3.94
Granted	1,311		10.36
Exercised	(886	)	4.33
Canceled	(302	)	7.58
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

Summary of Stock Options Outstanding

The following table summarizes information about stock options outstanding at December 31, 2015:



	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 —– $1.63	2,995	3.9	$	0.94	2,995	$	0.94
$1.88 —– $6.90	1,853	5.1	5.14		1,095	5.51
$6.98 —– $8.57	1,667	4.9	7.81		1,203	7.84
$8.58 —– $15.15	1,525	5.7	10.72		658	10.34
$16.01 —– $16.01	130	5.3	16.01		50	16.01
Total	8,170	4.7	5.36		6,001	4.31

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, 2012	248		$	5.53
Granted	285		6.92
Vested	(107	)	6.08
Canceled	(8	)	7.07
Outstanding at December 31, 2013	418		6.31
Granted	1,250		8.68
Vested	(281	)	7.38
Canceled	(42	)	7.56
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

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,
	2015		2014		2013
Proceeds from common stock issued under ESPP	$	2,497	$	1,531	$	1,047
Shares of common stock issued	499		410		327
Weighted-average price per share	$	5.00	$	3.73	$	3.20

INCOME TAXES (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015			2014			2013
United States	$	(22,120	)	$	(8,732	)	$	(26,118	)
Foreign	1,417			1,446			1,068
Total	$	(20,703	)	$	(7,286	)	$	(25,050	)

Schedule of Provision for Income Taxes

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



	Year Ended December 31,
	2015			2014			2013
Current:
Federal	$	—		$	—		$	—
State	44			85			—
Foreign	693			716			865
	737			801			865
Deferred:
Federal	652			—			—
State	41			—			—
Foreign	(51		)	(35		)	(2		)
	642			(35		)	(2		)
Provision for income taxes	$	1,379		$	766		$	863

Schedule of Effective Income Tax Rate Reconciliation



	Year Ended December 31,
	2015			2014			2013
Income tax benefit at statutory federal rate	$	(7,039	)	$	(2,477	)	$	(8,517	)
State taxes, net of federal benefit	56			(4,576		)	(883		)
Change in valuation allowance	7,812			16,646			8,353
Foreign tax rate and tax law differential	(29		)	(43		)	237
Tax credits	(1,553		)	(5,619		)	—
Stock-based compensation	1,932			957			1,191
Other permanent items	61			231			220
Other nondeductible/nontaxable items	(72		)	(4,586		)	(2		)
Uncertain tax positions	211			233			264
Provision for income taxes	$	1,379		$	766		$	863

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, 2015 and 2014 is as follows (in thousands):



	December 31,
	2015			2014
Deferred tax assets:
Allowances and reserves	$	14,639		$	18,771
Net operating loss and tax credit carryforwards	46,812			28,511
Stock-based compensation	3,055			2,154
Deferred revenue	5,966			3,843
Fixed assets and intangibles	6,830			9,163
Other	3,327			2,023
Subtotal	80,629			64,465
Less valuation allowance	(80,529		)	(64,428		)
Total deferred tax assets, net of valuation allowance	100			37
Deferred tax liabilities:
Goodwill	(693		)	—
Total deferred tax liabilities	(693		)	—
Net deferred tax asset/(liability)	$	(593	)	$	37

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,
	2015			2014		2013
Unrecognized tax benefits—at beginning of year	$	4,426		$	376	$	160
Increases in balances related to tax positions taken in prior years	14			1,895		79
Increases in balances related to tax positions taken in current year	1,053			2,155		137
Lapses in statutes of limitations	(11		)	—		—
Unrecognized tax benefits—at end of year	$	5,482		$	4,426	$	376

NET LOSS PER SHARE (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015	2014	2013
Stock options to purchase common stock	8,646	8,502	8,196
Unvested restricted stock units	1,506	1,258	381
Warrants to purchase common stock	111	195	308
Total	10,263	9,955	8,885

SEGMENT AND GEOGRAPHIC INFORMATION (Tables)

12 Months Ended

Dec. 31, 2015

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,
	2015		2014		2013
United States	$	303,195	$	294,549	$	192,881
International	54,054		49,355		39,965
Total	$	357,249	$	343,904	$	232,846

Long-Lived Assets



	As of December 31,
	2015		2014		2013
United States	$	21,913	$	20,037	$	16,262
China	7,950		9,585		7,130
Other	2,255		1,202		1,461
Total	$	32,118	$	30,824	$	24,853

Quarterly Financial Information (Unaudited) (Tables)

12 Months Ended

Dec. 31, 2015

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 2015 and 2014 (in thousands, except per share data):



	Years Ended December 31, 2015
	March 31			June 30			September 30			December 31

Net revenues	$	86,653		$	102,093		$	102,874		$	65,629
Cost of revenues	58,629			69,066			71,408			49,929
Gross profit	28,024			33,027			31,466			15,700
Operating expenses:
Research and development	13,430			12,786			12,059			12,544
Sales and marketing	11,937			12,508			10,510			10,922
General and administrative	8,205			8,102			7,118			7,405
Total operating expenses	33,572			33,396			29,687			30,871
Income (loss) from operations	(5,548		)	(369		)	1,779			(15,171		)
Other expense, net	(605		)	(8		)	(844		)	63
Income (loss) before income taxes	(6,153		)	(377		)	935			(15,108		)
Provision for income taxes	(167		)	(226		)	(311		)	(675		)
Net income (loss)	$	(6,320	)	$	(603	)	$	624		$	(15,783	)
Net income (loss) per share, basic	$	(0.14	)	$	(0.01	)	$	0.01		$	(0.35	)
Net income (loss) per share, diluted	$	(0.14	)	$	(0.01	)	$	0.01		$	(0.35	)

	Years Ended December 31, 2014
	March 31			June 30			September 30			December 31
Net revenues	$	57,580		$	82,004		$	99,113		$	105,207
Cost of revenues	38,925			55,172			66,592			70,172
Gross profit	18,655			26,832			32,521			35,035
Operating expenses:
Research and development	9,086			11,148			12,112			13,040
Sales and marketing	8,828			10,493			9,884			11,798
General and administrative	6,526			7,679			8,632			8,246
Total operating expenses	24,440			29,320			30,628			33,084
Income (loss) from operations	(5,785		)	(2,488		)	1,893			1,951
Other expense, net	(342		)	(428		)	(953		)	(1,134		)
Income (loss) before income taxes	(6,127		)	(2,916		)	940			817
Provision for income taxes	(109		)	(115		)	(127		)	(415		)
Net income (loss)	$	(6,236	)	$	(3,031	)	$	813		$	402
Net income (loss) per share, basic	$	(0.15	)	$	(0.07	)	$	0.02		$	0.01
Net income (loss) per share, diluted	$	(0.15	)	$	(0.07	)	$	0.02		$	0.01

DESCRIPTION OF BUSINESS - Narrative (Details)	Dec. 31, 2015 country system watt microinverter
Microinverter
Product Information [Line Items]
Number of product shipped, more than \| microinverter	10,300,000
Gigawatts, over \| watt	2,500,000,000
Residential and Commercial Systems
Product Information [Line Items]
Number of product deployed, more than \| system	430,000
Number of countries in which product is deployed, over \| country	100

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Dec. 31, 2015 USD ($) deliverable factor	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items]
Allowance for doubtful accounts	$ 1,808,000				$ 569,000				$ 1,808,000	$ 569,000	$ 2,000,000	$ 1,177,000
Impairment of intangible assets									$ 0	0	0
Number of factors considered in estimating replacement cost \| factor									3
Research and development expense	$ 12,544,000	$ 12,059,000	$ 12,786,000	$ 13,430,000	$ 13,040,000	$ 12,112,000	$ 11,148,000	$ 9,086,000	$ 50,819,000	$ 45,386,000	$ 34,524,000
Stock-based compensation requisite service period									4 years
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									1 year
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
Maximum \| Enlighten
Fair Value, Option, Quantitative Disclosures [Line Items]
Percent of revenue represented by product line or service, less than									2.00%
Revenue recognition period									10 years

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Schedule of Activity in Allowance for Doubtful Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Doubtful Accounts Receivable [Roll Forward]
Balance, at beginning of year	$ 569	$ 2,000	$ 1,177
Net charges to expenses	1,502	711	678
Write-offs, net of recoveries	(263)	(2,142)	145
Balance, at end of year	$ 1,808	$ 569	$ 2,000

INVENTORY - Summary of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Inventory Disclosure [Abstract]
Raw materials	$ 2,202	$ 3,429
Finished goods	38,598	18,161
Total inventory	$ 40,800	$ 21,590

PROPERTY AND EQUIPMENT, NET - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 63,627	$ 54,601
Less accumulated depreciation and amortization	(31,509)	(23,777)
Property and equipment, net	$ 32,118	30,824
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]
Estimated Useful Life (Years)	5 years
Property and equipment, gross	$ 34,694	28,923
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 3,556	3,032
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	$ 2,699	2,194
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	$ 11,041	8,905
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	$ 8,643	6,636
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	$ 2,994	$ 4,911

PROPERTY AND EQUIPMENT, NET - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Abstract]
Depreciation and amortization	$ 10.0	$ 8.1	$ 7.0
Unamortized capitalized software costs	$ 3.3	$ 3.3

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS - Summary of Allocated Purchase Price to Acquired Tangible and Identifiable Intangible Assets Based on Estimated Fair Value (Details) - USD ($) $ in Thousands	Dec. 12, 2014	Dec. 31, 2015	Dec. 31, 2014
Net Assets Acquired
Goodwill		$ 3,745	$ 3,745
NPS
Total Purchase Price
Cash consideration	$ 2,535
Contingent consideration	2,300
Total purchase consideration	4,835
Net Assets Acquired
Property and equipment	190
Customer relationships	900
Goodwill	3,745	$ 3,745	$ 3,745
Net assets acquired	$ 4,835

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) - USD ($)		1 Months Ended		12 Months Ended
	Dec. 12, 2014	Oct. 31, 2015	Jul. 31, 2014	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill				$ 3,745,000	$ 3,745,000
Aggregate amortization expense				500,000	100,000
ASIC
Business Acquisition [Line Items]
Licensed technology term		3 years
Patents
Business Acquisition [Line Items]
Intangible assets, estimated useful life			3 years
Customer relationships
Business Acquisition [Line Items]
Intangible assets, estimated useful life			5 years
NPS
Business Acquisition [Line Items]
Total purchase consideration	$ 4,835,000
Purchase consideration, cash	2,535,000
Purchase consideration, cash withheld	300,000
Contingent consideration	2,300,000
Goodwill	$ 3,745,000			3,745,000	3,745,000
Contingent consideration, minimum				0
Contingent consideration, maximum				$ 5,500,000
NPS \| General and Administrative Expenses
Business Acquisition [Line Items]
Acquisition related costs					$ 200,000

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS - Summary of Goodwill and Purchased Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 12, 2014
Business Acquisition [Line Items]
Goodwill	$ 3,745	$ 3,745
Intangibles assets with finite lives:
Total	1,934
Total purchased intangibles, net	2,220	1,811
NPS
Business Acquisition [Line Items]
Goodwill, gross	3,745	3,745
Goodwill	3,745	3,745	$ 3,745
Other indefinite-lived intangibles	286	286
Intangibles assets with finite lives:
Total purchased intangibles, gross	2,851	1,936
Total purchased intangibles, accumulated amortization	(631)	(125)
Total purchased intangibles, net	2,220	1,811
Customer relationships \| NPS
Intangibles assets with finite lives:
Gross	900	900
Accumulated Amortization	(180)	0
Total	720	900
Patents and licensed technology \| NPS
Intangibles assets with finite lives:
Gross	1,665	750
Accumulated Amortization	(451)	(125)
Total	$ 1,214	$ 625

BUSINESS COMBINATION, GOODWILL AND INTANGIBLE ASSETS - Schedule of Estimated Future Amortization Expense Related to Finite-lived Intangible Assets (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract]
2016	$ 735
2017	610
2018	409
2019	180
Total	$ 1,934

ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued Liabilities [Abstract]
Salaries, commissions, incentive compensation and benefits	$ 5,402	$ 14,871
Customer rebates and sales incentives	8,274	5,083
Freight	3,063	1,917
Other	2,553	4,165
Total	$ 19,292	$ 26,036

WARRANTY OBLIGATIONS - Summary of Warranty Activity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Changes in the Company's product warranty liability
Balance, at beginning of year	$ 33,940	$ 30,432	$ 21,338
Accruals for warranties issued during the year	4,383	4,309	6,303
Changes in estimates	31	8,391	10,303
Settlements	(7,269)	(8,793)	(7,512)
Increase due to accretion expense	1,001	195	0
Fair value adjustments	(1,539)	(594)	0
Balance, at end of year	30,547	33,940	30,432
Less current portion	(7,072)	(7,607)	(4,942)
Long-term portion	$ 23,475	$ 26,333	$ 25,490

WARRANTY OBLIGATIONS - Narrative (Details) microinverter in Millions, $ in Millions	3 Months Ended	12 Months Ended			30 Months Ended	42 Months Ended	54 Months Ended
	Sep. 30, 2013 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)	Dec. 31, 2015 microinverter	Dec. 31, 2015 microinverter	Jun. 30, 2012 microinverter
Minimum
Product Liability Contingency [Line Items]
Product warranty, term		15 years
Maximum
Product Liability Contingency [Line Items]
Product warranty, term		25 years
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		$ 0.7	$ 1.3
Second generation \| Failure rate
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates		0.8	8.6	$ 19.5
Third generation
Product Liability Contingency [Line Items]
Number of units sold \| microinverter						3.9
Third generation \| Failure rate
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates	$ (3.1)
Fourth generation
Product Liability Contingency [Line Items]
Number of units sold \| microinverter					5.4
Fourth generation \| Replacement cost
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates		$ (1.5)		$ (1.9)
All product generations \| Replacement cost
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates			(1.5)
Net decrease in warranty expense due to changes in warranty variables estimates			$ 0.2
Second and third generation \| Minimum
Product Liability Contingency [Line Items]
Product warranty, term				15 years
Second and third generation \| Maximum
Product Liability Contingency [Line Items]
Increase (decrease) in warranty expense due to changes in warranty variables estimates				$ (4.2)
Product warranty, term				25 years

FAIR VALUE MEASUREMENTS - Schedule of Financial Instruments Measured at Fair Value on a Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Level 2
Assets:
Foreign currency forward contracts	$ 86	$ 76
Liabilities:
Foreign currency forward contracts	9	0
Level 3 \| Warranty obligations
Liabilities:
Warranty obligations/Contingent consideration	6,182	3,562	$ 0
Level 3 \| Contingent consideration
Liabilities:
Warranty obligations/Contingent consideration	$ 473	$ 2,300

FAIR VALUE MEASUREMENTS - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Contingent consideration earnout period	1 year
Warranty obligations \| Recurring \| Level 3
Derivative [Line Items]
Fair value of liability	$ 6,182	$ 3,562	$ 0
Contingent consideration \| Recurring \| Level 3
Derivative [Line Items]
Fair value of liability	473	2,300
Contingent consideration \| Discounted cash flows \| Recurring \| Level 3
Derivative [Line Items]
Fair value of liability	2,300
Decrease to fair value measurement as a result of 100 basis point increase	(162)
Increase to fair value measurement as a result of 100 basis point decrease	173
Contingent consideration \| Discounted cash flows \| Minimum \| Recurring \| Level 3
Derivative [Line Items]
Probability adjusted level of revenue	2,600
Contingent consideration \| Discounted cash flows \| Maximum \| Recurring \| Level 3
Derivative [Line Items]
Probability adjusted level of revenue	17,000
Foreign exchange forward \| Not designated as hedging instrument
Derivative [Line Items]
Notional amount of foreign currency	2,400	1,500
Net gain (loss) on foreign currency	$ 300	$ 300	$ (400)

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, 2015	Dec. 31, 2014
Warranty Obligations at Fair Value [Roll Forward]
Beginning balance	$ 3,562	$ 0
Accruals for warranties issued during period	4,140	3,989
Changes in estimates	(755)	26
Settlements	(227)	(54)
Increase due to accretion expense	1,001	195
Fair value adjustments	(1,539)	(594)
Ending balance	$ 6,182	$ 3,562

FAIR VALUE MEASUREMENTS - Schedule of Reconciliation of Beginning and Ending Balances of Contingent Consideration Measured at Fair Value (Details) - Recurring - Level 3 - Contingent consideration $ in Thousands	12 Months Ended
	Dec. 31, 2015 USD ($)
Contingent Consideration at Fair Value [Roll Forward]
Beginning balance	$ 2,300
Fair value adjustment to contingent consideration	(1,827)
Ending balance	$ 473

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, 2015
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%
Credit-adjusted risk-free rate	25.00%
Contingent consideration
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Risk-adjusted discount rate	17.00%

REVOLVING CREDIT FACILITY - Narrative (Details) - Line of credit - Wells Fargo Bank - Revolving credit facility - USD ($)	Nov. 07, 2012	Dec. 31, 2015	Dec. 18, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Credit line facility	$ 50,000,000.0
Uncommitted accordion feature			$ 25,000,000.0
Amount of liquidity required for debt compliance	15,000,000.0
Amount of undrawn credit for debt compliance	$ 5,000,000.0
Outstanding borrowings		$ 17,000,000		$ 0
Remaining borrowing capacity		$ 27,700,000
Weighted-average interest rate		4.30%
LIBOR \| Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	1.00%
Unused commitment fee percent	0.25%
LIBOR \| Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.75%
Unused commitment fee percent	0.375%

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Commitments and Contingencies Disclosure [Abstract]
Rent expense	$ 3.2	$ 2.6	$ 2.4
Purchase obligation	$ 51.0

COMMITMENTS AND CONTINGENCIES - Schedule of Minimum Lease Payments Under Noncancelable Operating Leases (Details) $ in Thousands	Dec. 31, 2015 USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2016	$ 2,618
2017	2,711
2018	2,700
2019	2,739
2020	2,577
Thereafter	4,789
Total minimum lease payments	$ 18,134

STOCK-BASED COMPENSATION - Narrative (Details)			12 Months Ended
STOCK-BASED COMPENSATION - Narrative (Details)	Jan. 01, 2016 shares	Mar. 31, 2014	Dec. 31, 2015 USD ($) purchase_period $ / shares shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares	Dec. 31, 2012 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options outstanding (shares)			8,170,000	8,632,000	8,509,000	8,169,000
Total unrecognized compensation cost \| $			$ 18,600,000
Weighted-average period			2 years 6 months 15 days
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 \| $			$ 4,900,000	$ 5,500,000	$ 3,200,000
Number of options outstanding that were vested and expected to vest (shares)			8,000,000
Weighted-average fair value, vested (usd per share) \| $ / shares			$ 5.31
Weighted-average remaining contractual term, vested			4 years 8 months 16 days
Aggregate intrinsic value, exercisable shares \| $			$ 7,800,000
Number of shares exercisable (shares)			6,001,000
Common stock fair value (usd per share) \| $ / shares			$ 3.51
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of units vested \| $			$ 4,200,000	$ 3,200,000	$ 800,000
Weighted average remaining contractual term			1 year 4 months 12 days
Intrinsic value of restricted stock units outstanding \| $			$ 4,600,000
After March 31, 2014 \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of years of historical stock price volatility		2 years
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)			3,500,000
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)			1,035,944
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 \| Subsequent event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in shares authorized for issuance under plan (shares)	2,061,949
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)			366,432
Issue of common stock (shares)			669,603
Annual share increase in reserved shares on each January 1 (shares)			330,396
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
2011 Employee Stock Purchase Plan (ESPP) \| Subsequent event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual share increase in reserved shares on each January 1 (shares)	330,396

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, 2015	Dec. 31, 2014	Dec. 31, 2013
The Fair Value of Each Option Granted During the Period [Abstract]
Expected term (in years)	4 years 6 months	4 years 6 months	4 years 4 months 24 days
Expected volatility	72.50%	67.70%	68.40%
Annual risk-free rate of return	1.40%	1.40%	1.00%
Dividend yield	0.00%	0.00%	0.00%
Weighted-average fair value on grant date (usd per share)	$ 4.68	$ 5.64	$ 3.84

STOCK-BASED COMPENSATION - Summary of Total Stock Based Compensation Expense Components (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 12,696	$ 9,740	$ 6,849
Cost of revenues
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,217	816	438
Research and development
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	4,559	3,127	2,110
Sales and marketing
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	3,162	2,487	1,812
General and administrative
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 3,758	$ 3,310	$ 2,489

STOCK-BASED COMPENSATION - Summary of Stock Based Compensation Expense Associated with Each Type of Award (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 12,696	$ 9,740	$ 6,849
Stock options and restricted stock units
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	10,685	8,845	6,314
ESPP
Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,011	$ 895	$ 535

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Shares
Options outstanding, beginning (shares)	8,632	8,509	8,169
Granted (shares)	1,289	1,311	1,506
Exercised (shares)	(1,079)	(886)	(822)
Canceled (shares)	(672)	(302)	(344)
Options outstanding, ending (shares)	8,170	8,632	8,509
Weighted- Average Exercise Price per Share
Options outstanding, beginning (usd per share)	$ 4.75	$ 3.94	$ 3.28
Granted (usd per share)	8.20	10.36	7.17
Exercised (usd per share)	1.40	4.33	1.69
Canceled (usd per share)	9.31	7.58	7.74
Options outstanding, ending (usd per share)	$ 5.36	$ 4.75	$ 3.94

STOCK-BASED COMPENSATION - Summary of Stock Options Outstanding (Details) shares in Thousands	12 Months Ended
	Dec. 31, 2015 $ / shares shares
Exercise Price Range of Options Outstanding and Options Exercisable [Line Items]
Options Outstanding - Number of Shares (shares) \| shares	8,170
Options Outstanding - Weighted- Average Remaining Life	4 years 8 months 24 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 5.36
Options Exercisable - Number of Shares Exercisable (shares) \| shares	6,001
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 4.31
$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)	$ 1.63
Options Outstanding - Number of Shares (shares) \| shares	2,995
Options Outstanding - Weighted- Average Remaining Life	3 years 10 months 10 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 0.94
Options Exercisable - Number of Shares Exercisable (shares) \| shares	2,995
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 0.94
$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)	1.88
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 6.9
Options Outstanding - Number of Shares (shares) \| shares	1,853
Options Outstanding - Weighted- Average Remaining Life	5 years 1 month 10 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 5.14
Options Exercisable - Number of Shares Exercisable (shares) \| shares	1,095
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 5.51
$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)	6.98
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 8.57
Options Outstanding - Number of Shares (shares) \| shares	1,667
Options Outstanding - Weighted- Average Remaining Life	4 years 11 months 6 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 7.81
Options Exercisable - Number of Shares Exercisable (shares) \| shares	1,203
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 7.84
$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)	8.58
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 15.15
Options Outstanding - Number of Shares (shares) \| shares	1,525
Options Outstanding - Weighted- Average Remaining Life	5 years 8 months 10 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 10.72
Options Exercisable - Number of Shares Exercisable (shares) \| shares	658
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 10.34
$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)	16.01
Range of Exercise Prices - Upper Range Limit (usd per share)	$ 16.01
Options Outstanding - Number of Shares (shares) \| shares	130
Options Outstanding - Weighted- Average Remaining Life	5 years 3 months 12 days
Options Outstanding - Weighted- Average Exercise Price (usd per share)	$ 16.01
Options Exercisable - Number of Shares Exercisable (shares) \| shares	50
Options Exercisable - Weighted- Average Exercise Price (usd per share)	$ 16.01

STOCK-BASED COMPENSATION - Summary of Restricted Stock Unit Activity (Details) - Restricted stock units - $ / shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock Units
Outstanding units, beginning (shares)	1,345	418	248
Granted (shares)	683	1,250	285
Vested (shares)	(488)	(281)	(107)
Canceled (shares)	(227)	(42)	(8)
Outstanding units, ending (shares)	1,313	1,345	418
Weighted Average Fair Value per Share at Grant Date
Outstanding units, beginning (usd per share)	$ 8.25	$ 6.31	$ 5.53
Granted (usd per share)	11.22	8.68	6.92
Vested (usd per share)	8.58	7.38	6.08
Canceled (usd per share)	10.32	7.56	7.07
Outstanding units, ending (usd per share)	$ 9.31	$ 8.25	$ 6.31

STOCK-BASED COMPENSATION - Summary of ESPP Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Proceeds from common stock issued under ESPP	$ 2,497	$ 1,531	$ 1,047
Shares of common stock issued (shares)	499	410	327
Weighted-average price per share (usd per share)	$ 5.00	$ 3.73	$ 3.20

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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
United States									$ (22,120)	$ (8,732)	$ (26,118)
Foreign									1,417	1,446	1,068
Income (loss) before income taxes	$ (15,108)	$ 935	$ (377)	$ (6,153)	$ 817	$ 940	$ (2,916)	$ (6,127)	$ (20,703)	$ (7,286)	$ (25,050)

INCOME TAXES - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal									$ 0	$ 0	$ 0
State									44	85	0
Foreign									693	716	865
Total									737	801	865
Deferred:
Federal									652	0	0
State									41	0	0
Foreign									(51)	(35)	(2)
Total									642	(35)	(2)
Provision for income taxes	$ 675	$ 311	$ 226	$ 167	$ 415	$ 127	$ 115	$ 109	$ 1,379	$ 766	$ 863

INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
INCOME TAXES - Narrative (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Federal statutory income tax rate	34.00%	34.00%	34.00%
Undistributed earnings of foreign subsidiaries	$ 3.5
Increase in equity if and when deferred tax assets are ultimately realized	6.0
Increase to unrecognized tax benefits	1.1
Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	83.2
Federal \| Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	7.2
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	78.3
State \| Research Tax Credit Carryforward
Operating Loss Carryforwards [Line Items]
Research tax credit carryforwards	$ 7.1

INCOME TAXES - Schedule of Effective Income Tax Rate Reconciliation (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Effective Income Tax Rate Reconciliation, Percent [Abstract]
Income tax benefit at statutory federal rate									$ (7,039)	$ (2,477)	$ (8,517)
State taxes, net of federal benefit									56	(4,576)	(883)
Change in valuation allowance									7,812	16,646	8,353
Foreign tax rate and tax law differential									(29)	(43)	237
Tax credits									(1,553)	(5,619)	0
Stock-based compensation									1,932	957	1,191
Other permanent items									61	231	220
Other nondeductible/nontaxable items									(72)	(4,586)	(2)
Uncertain tax positions									211	233	264
Provision for income taxes	$ 675	$ 311	$ 226	$ 167	$ 415	$ 127	$ 115	$ 109	$ 1,379	$ 766	$ 863

INCOME TAXES - Schedule of Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Deferred tax assets:
Allowances and reserves	$ 14,639	$ 18,771
Net operating loss and tax credit carryforwards	46,812	28,511
Stock-based compensation	3,055	2,154
Deferred revenue	5,966	3,843
Fixed assets and intangibles	6,830	9,163
Other	3,327	2,023
Subtotal	80,629	64,465
Less valuation allowance	(80,529)	(64,428)
Total deferred tax assets, net of valuation allowance	100	37
Deferred tax liabilities:
Goodwill	(693)	0
Total deferred tax liabilities	(693)	0
Net deferred tax liability	$ (593)
Net deferred tax asset		$ 37

INCOME TAXES - Schedule of Reconciliation of Total Amounts of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits—at beginning of year	$ 4,426	$ 376	$ 160
Increases in balances related to tax positions taken in prior years	14	1,895	79
Increases in balances related to tax positions taken in current year	1,053	2,155	137
Lapses in statutes of limitations	(11)	0	0
Unrecognized tax benefits—at end of year	$ 5,482	$ 4,426	$ 376

CONCENTRATION OF CREDIT RISK AND MAJOR CUSTOMERS - Narrative (Details) - customer	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Accounts Receivable \| Credit Concentration Risk
Revenue, Major Customer [Line Items]
Number of customers considered to give rise to concentration risk	1	2
Percentage of concentration risk	15.00%
Net Revenue \| Credit Concentration Risk
Revenue, Major Customer [Line Items]
Number of customers considered to give rise to concentration risk	2	2
Net Revenue \| Customer Concentration Risk
Revenue, Major Customer [Line Items]
Number of customers considered to give rise to concentration risk			3
Customer Providing Largest Concentration of Receivable \| Accounts Receivable \| Credit Concentration Risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk		15.00%
Customer Providing Second Largest Concentration of Receivable \| Accounts Receivable \| Credit Concentration Risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk		11.00%
Customer Accounting for the Largest Concentration of Revenue \| Net Revenue \| Customer Concentration Risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk	17.00%	24.00%	15.00%
Customer Accounting for Second Largest Concentration of Revenue \| Net Revenue \| Customer Concentration Risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk	12.00%	16.00%	14.00%
Customer Accounting for Third Largest Concentraion \| Net Revenue \| Customer Concentration Risk
Revenue, Major Customer [Line Items]
Percentage of concentration risk			11.00%

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, 2015	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	10,263	9,955	8,885
Stock options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	8,646	8,502	8,196
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	1,506	1,258	381
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (shares)	111	195	308

SEGMENT AND GEOGRAPHIC INFORMATION - Narrative (Details)	12 Months Ended
	Dec. 31, 2015 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, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues	$ 65,629	$ 102,874	$ 102,093	$ 86,653	$ 105,207	$ 99,113	$ 82,004	$ 57,580	$ 357,249	$ 343,904	$ 232,846
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									303,195	294,549	192,881
International
Revenues from External Customers and Long-Lived Assets [Line Items]
Revenues									$ 54,054	$ 49,355	$ 39,965

SEGMENT AND GEOGRAPHIC INFORMATION - Summary of Long-Lived Assets by Geographic Region (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	$ 32,118	$ 30,824	$ 24,853
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	21,913	20,037	16,262
China
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	7,950	9,585	7,130
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Total	$ 2,255	$ 1,202	$ 1,461

Quarterly Financial Information (Unaudited) - Schedule of Quarterly Financial Information (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Net revenues	$ 65,629	$ 102,874	$ 102,093	$ 86,653	$ 105,207	$ 99,113	$ 82,004	$ 57,580	$ 357,249	$ 343,904	$ 232,846
Cost of revenues	49,929	71,408	69,066	58,629	70,172	66,592	55,172	38,925	249,032	230,861	165,430
Gross profit	15,700	31,466	33,027	28,024	35,035	32,521	26,832	18,655	108,217	113,043	67,416
Operating expenses:
Research and development	12,544	12,059	12,786	13,430	13,040	12,112	11,148	9,086	50,819	45,386	34,524
Sales and marketing	10,922	10,510	12,508	11,937	11,798	9,884	10,493	8,828	45,877	41,003	31,080
General and administrative	7,405	7,118	8,102	8,205	8,246	8,632	7,679	6,526	30,830	31,083	23,970
Total operating expenses	30,871	29,687	33,396	33,572	33,084	30,628	29,320	24,440	127,526	117,472	89,574
Income (loss) from operations	(15,171)	1,779	(369)	(5,548)	1,951	1,893	(2,488)	(5,785)	(19,309)	(4,429)	(22,158)
Other expense, net	63	(844)	(8)	(605)	(1,134)	(953)	(428)	(342)	(1,394)	(2,857)	(2,892)
Income (loss) before income taxes	(15,108)	935	(377)	(6,153)	817	940	(2,916)	(6,127)	(20,703)	(7,286)	(25,050)
Provision for income taxes	(675)	(311)	(226)	(167)	(415)	(127)	(115)	(109)	(1,379)	(766)	(863)
Net income (loss)	$ (15,783)	$ 624	$ (603)	$ (6,320)	$ 402	$ 813	$ (3,031)	$ (6,236)	$ (22,082)	$ (8,052)	$ (25,913)
Net income (loss) per share, basic (usd per share)	$ (0.35)	$ 0.01	$ (0.01)	$ (0.14)	$ 0.01	$ 0.02	$ (0.07)	$ (0.15)
Net income (loss) per share, diluted (usd per share)	$ (0.35)	$ 0.01	$ (0.01)	$ (0.14)	$ 0.01	$ 0.02	$ (0.07)	$ (0.15)