Enphase Energy (ENPH) 10-Q 6 Nov 18 2018 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2018	Nov. 01, 2018
Document and Entity Information [Abstract]
Entity Registrant Name	Enphase Energy, Inc.
Entity Central Index Key	1,463,101
Document Type	10-Q
Document Period End Date	Sep. 30, 2018
Amendment Flag	false
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q3
Current Fiscal Year End	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		106,328,107

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 116,164	$ 29,144
Accounts receivable, net of allowances of $2,167 and $2,378 at September 30, 2018 and December 31, 2017, respectively	54,117	65,346
Inventory	17,886	25,999
Prepaid expenses and other assets	21,631	9,957
Total current assets	209,798	130,446
Property and equipment, net	20,331	26,483
Intangible assets, net	36,078	515
Goodwill	24,783	3,664
Other assets	35,520	8,039
Total assets	326,510	169,147
Current liabilities:
Accounts payable	28,103	28,747
Accrued liabilities	41,562	22,447
Deferred revenues, current	32,015	15,691
Warranty obligations, current (includes $4,110 and $2,240 measured at fair value at September 30, 2018 and December 31, 2017, respectively)	9,117	7,427
Debt, current	24,125	17,429
Total current liabilities	134,922	91,741
Long-term liabilities:
Deferred revenues, noncurrent	74,065	29,941
Warranty obligations, noncurrent (includes $9,456 and $7,551 measured at fair value at September 30, 2018 and December 31, 2017, respectively)	23,067	22,389
Other liabilities	2,393	1,880
Debt, noncurrent	87,907	32,322
Total liabilities	322,354	178,273
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, 150,000 shares and 125,000 shares authorized; and 106,322 and 85,914 shares issued and outstanding at September 30, 2018 and December 31, 2017, respectively	1	1
Additional paid-in capital	351,173	287,256
Accumulated deficit	(347,011)	(295,727)
Accumulated other comprehensive loss	(7)	(656)
Total stockholders’ equity (deficit)	4,156	(9,126)
Total liabilities and stockholders’ equity	$ 326,510	$ 169,147

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Allowances, accounts receivable	$ 2,167	$ 2,378
Warranty obligations, current at fair value	4,110	2,240
Warranty obligations, non-current at fair value	$ 9,456	$ 7,551
Preferred stock, par value (in usd per share)	$ 0.00001	$ 0.00001
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in usd per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized (in shares)	150,000,000	125,000,000
Common stock, shares issued (in shares)	106,322,000	85,914,000
Common stock, shares outstanding (in shares)	106,322,000	85,914,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Income Statement [Abstract]
Net revenues	$ 78,002	$ 77,038	$ 223,870	$ 206,492
Cost of revenues	52,738	60,577	157,589	169,438
Gross profit	25,264	16,461	66,281	37,054
Operating expenses:
Research and development	8,165	7,397	25,247	24,949
Sales and marketing	7,375	5,453	20,430	18,186
General and administrative	7,510	5,441	21,423	16,238
Restructuring charges	2,588	4,071	2,588	14,927
Total operating expenses	25,638	22,362	69,688	74,300
Loss from operations	(374)	(5,901)	(3,407)	(37,246)
Other expense, net
Interest expense	(2,469)	(1,760)	(7,031)	(5,979)
Other income (expense)	(379)	623	(1,077)	1,771
Total other expense, net	(2,848)	(1,137)	(8,108)	(4,208)
Loss before income taxes	(3,222)	(7,038)	(11,515)	(41,454)
Income tax (provision) benefit	(248)	184	(821)	(798)
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)	$ (0.08)	$ (0.13)	$ (0.52)
Shares used in per share calculation:
Basic and diluted (in shares)	102,798	84,862	97,257	81,993

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Statement of Comprehensive Income [Abstract]
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Other comprehensive loss:
Foreign currency translation adjustments	346	(296)	649	(173)
Comprehensive loss	$ (3,124)	$ (7,150)	$ (11,687)	$ (42,425)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Cash flows from operating activities:
Net loss	$ (12,336)	$ (42,252)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	6,950	6,763
Provision for doubtful accounts	668	911
Asset impairment charges	1,636	1,638
Amortization of debt issuance costs	1,880	1,337
Stock-based compensation	9,911	5,277
Changes in operating assets and liabilities:
Accounts receivable	10,671	(8,761)
Inventory	8,112	6,644
Prepaid expenses and other assets	(3,995)	(5,110)
Increase (Decrease) in Intangible Assets, Current	(6,000)	0
Accounts payable, accrued and other liabilities	4,672	3,051
Warranty obligations	2,368	(1,062)
Deferred revenues	(10,280)	5,036
Net cash provided by (used in) operating activities	14,257	(26,528)
Cash flows from investing activities:
Purchases of property and equipment	(2,384)	(3,609)
Acquisition	(9,000)	0
Net cash used in investing activities	(11,384)	(3,609)
Cash flows from financing activities:
Proceeds from issuance of common stock, net of issuance costs	19,771	26,425
Proceeds from debt	68,352	24,240
Principal payments on term debt	(5,664)	0
Payments under revolving credit facility	0	(10,100)
Proceeds from issuance of common stock under employee stock plans	2,151	174
Net cash provided by financing activities	84,610	40,739
Effect of exchange rate changes on cash	(463)	512
Net increase in cash and cash equivalents	87,020	11,114
Cash and cash equivalents—Beginning of period	29,144	17,764
Cash and cash equivalents—End of period	116,164	28,878
Supplemental disclosures of non-cash investing and financing activities:
Acquisition funded by issuance of common stock	19,219	0
Acquisition funded by accrued liabilities	6,000	0
Purchases of fixed assets included in accounts payable	125	871
Warrants issued in connection with debt	$ 0	$ 1,447

DESCRIPTION OF BUSINESS AND BAS

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION	DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION Description of Business Enphase Energy, Inc. and subsidiaries (the “Company”) deliver simple, innovative and reliable energy management solutions that advance the worldwide potential of renewable energy. The Company’s semiconductor-based microinverter system converts direct current (DC) electricity to alternating current (AC) electricity at the individual solar module level and brings a system-based, high technology approach to solar energy generation leveraging the Company’s design expertise across power electronics, semiconductors, networking, and cloud-based software technologies. Since inception, the Company has shipped over 18 million microinverters, representing over 4 gigawatts of solar photovoltaic (PV) generating capacity, and more than 820,000 Enphase residential and commercial systems have been deployed in over 120 countries. Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements are presented in accordance with accounting principles generally accepted in the U.S, or GAAP. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation. Unaudited Interim Financial Information These accompanying unaudited condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial reporting. In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments, consisting of normal recurring items, considered necessary to present fairly the Company's financial condition, results of operations, comprehensive loss and cash flows for the interim periods indicated. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the operating results for the full year. Certain information and footnote disclosures typically included in annual consolidated financial statements have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 . Other than as discussed in Note 2. “Revenue Recognition,” Note 11. “Stock-based Compensation” and Note 14. “ Acquisition ,” there have been no material changes in the Company’s significant accounting policies during the nine months ended September 30, 2018 , as compared to the significant accounting policies described in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 . Reference is made to the disclosures therein for a summary of the Company’s significant accounting policies. Use of Estimates The preparation of financial statements in conformity with 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. Significant estimates and assumptions reflected in the financial statements include revenue recognition, inventory valuation and accrued warranty obligations. 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. Recently Adopted Accounting Pronouncements In May 2014, the FASB issued Accounting Standards Update No. (“ASU”) 2014-09, “Revenue from Contracts with Customers,” amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The amended guidance, herein referred to as Topic 606, is effective for annual and interim reporting periods beginning after December 15, 2017, with early adoption permitted for public companies effective for annual and interim reporting periods beginning after December 15, 2016. The Company has adopted Topic 606 effective January 1, 2018, using the modified retrospective transition method. The Company recognized the cumulative effect of applying the new revenue standard as an adjustment to the opening balance of retained earnings on January 1, 2018. The comparative information has not been restated and continues to be reported under the accounting standards in effect for the period presented. See Note 2, “Revenue Recognition,” for additional accounting policy and transition disclosures. 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 was 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 standard, which was adopted in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows,” which requires companies to include amounts generally described as restricted cash and restricted cash equivalents in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The standard, which was adopted prospectively in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation." ASU 2017-09 was issued to provide clarity and reduce both 1) diversity in practice and 2) cost and complexity when applying the guidance in Topic 718 to a change in the terms or conditions of a share-based payment award. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting under Topic 718. ASU 2017-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The standard, which was adopted in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Effective In February 2016, the FASB issued ASU 2016-02, Leases (“ASU 2016-02”). The guidance will require lessees to recognize all leases, with certain exceptions, on their balance sheets, whether operating or financing, while continuing to recognize the expenses on their income statements in a manner similar to current practice. The guidance states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-to-use asset for the right to use the underlying asset for the lease term. The guidance will be effective for the Company beginning January 1, 2019 and early adoption is permitted. The Company will adopt ASU 2016-02 on January 1, 2019 and intends to elect the available practical expedients upon adoption. Upon adoption, the Company expects the consolidated balance sheet to include a right of use asset and a corresponding lease liability related to substantially all of the Company’s lease arrangements. The Company is evaluating the accounting, transition and disclosure requirements of the standard.

REVENUE RECOGNITION

REVENUE RECOGNITION	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
REVENUE RECOGNITION	REVENUE RECOGNITION On January 1, 2018, the Company adopted Topic 606 and applied the modified retrospective method to all contracts that were not completed as of January 1, 2018. Results for reporting periods beginning after January 1, 2018 are presented under Topic 606, while prior period amounts are not adjusted and continue to be reported under the accounting standards in effect in the prior period. The Company recorded a net reduction to opening equity of $38.9 million on January 1, 2018 for the cumulative effect of adopting Topic 606. The impact to net revenues from the adoption of Topic 606 for the nine months ended September 30, 2018 was a net increase of $2.8 million . Changes in accounting policies as a result of adopting Topic 606 and nature of goods The most significant impacts upon adoption of Topic 606 were how the Company accounts for revenue related to its Envoy communications device and related Enlighten service and the timing of when certain sales incentives are recognized. Under ASC 605 the Company’s Envoy communications device and Enlighten service were considered two units of accounting, and the portion of the consideration related to the hardware was recognized at the time of sale with the remaining consideration deferred and recognized over the estimated service period. Under ASC 606 the full consideration for these products represents a single performance obligation and is deferred and recognized over the estimated service period. This treatment resulted in a gross increase to deferred revenue of $77.5 million , an increase in deferred costs of $43.4 million and a net increase in accumulated deficit of $34.1 million upon adoption of ASC 606. The Company previously sold its Envoy communications device to certain customers under a long-term financing arrangement. Under ASC 605, this arrangement resulted in the recording of both deferred revenue and unbilled receivables on the Company’s condensed consolidated balance sheets. The Company’s opening entries related to ASC 606 included the netting of approximately $6.4 million of unbilled receivables against deferred revenue. Thus, the $77.5 million increase to deferred revenue noted above was partially offset by a $6.4 million reclassification of unbilled receivables to deferred revenue. Under ASC 605 the Company recorded certain contra revenue promotions at the later of the date revenue was recognized or the date at which the promotional offer was extended. Under ASC 606 all such contra revenue programs are treated as variable consideration and recognized at the time the related revenue is recorded. This change in timing resulted in an increase in accrued liabilities of approximately $5.6 million and an increase to accumulated deficit of the same amount upon adoption of ASC 606. This change in timing is not expected to have a material impact in subsequent periods. Topic 606 requires upfront contract acquisition costs, such as sales commissions, to be capitalized and amortized over the estimated life of the asset. For contracts that have a duration of less than one year, the Company follows the Topic 606 practical expedient and expenses these costs when incurred. Commissions related to the Company’s sale of monitoring hardware and service are capitalized and amortized over the period of the associated revenue, which is 6.5 years . This treatment resulted in an increase in deferred costs of approximately $0.8 million and a decrease in accumulated deficit of the same amount upon adoption of ASC 606. Revenues are recognized when control of the promised goods or services are transferred to the Company’s customers in an amount that reflects the consideration that is expected to be received in exchange for those goods or services. The Company generates all of its revenues from contracts with its customers. A description of principal activities from which the Company generates revenues follows. Products Delivered at a Point in Time The Company sells its products to customers in accordance with the terms of the related customer contracts. The Company generates revenues from sales of its microinverter systems, which include microinverter units and related accessories, an Envoy communications gateway and Enlighten service, communications accessories and AC Battery storage solutions to distributors, large installers, OEMs and strategic partners. Microinverter units, microinverter accessories, and AC Battery storage solutions are delivered to customers at a point in time, and in accordance with Topic 606, the Company recognizes revenue for these products when the Company transfers control of the product to the customer, which is generally upon shipment. Products Delivered Over Time The sale of an Envoy communications gateway includes the Company’s Enlighten cloud-based monitoring service. Under Topic 606 the full consideration for these products represents a single performance obligation and is deferred at the sale date and recognized over the estimated service period, which is 6.5 years . The Company also sells certain communication accessories that are delivered over time. The revenue from these products is recognized over the related service period, which is typically 5 or 12 years . Disaggregation of Revenue The Company has one business activity, which is the design, manufacture and sale of microinverter systems for the solar photovoltaic industry. The following table provides information about disaggregated revenue by primary geographical market and timing of revenue recognition for the Company’s single product line (in thousands): Three Months Ended Nine Months Ended Primary geographical markets: United States $ 54,880 $ 148,268 International 23,122 75,602 Total $ 78,002 $ 223,870 Timing of revenue recognition: Products transferred at a point in time $ 68,256 $ 193,564 Products and services transferred over time 9,746 30,306 Total $ 78,002 $ 223,870 Contract Balances As of September 30, 2018 , receivables, contract assets and contract liabilities from contracts with customers consist of the following (in thousands): September 30, 2018 Receivables $ 54,117 Short-term contract assets (Prepaid expenses and other assets) 12,876 Long-term contract assets (Other assets) 32,967 Short-term contract liabilities (Deferred revenues) 32,015 Long-term contract liabilities (Deferred revenues) 74,065 The Company receives payments from customers based upon contractual billing schedules. Accounts receivable are recorded when the right to consideration becomes unconditional. Contract assets include deferred product costs and commissions associated with the deferred revenue and will be amortized along with the associated revenue. The Company had no asset impairment charges related to contract assets in the nine months ended September 30, 2018 . Contract liabilities are recorded as deferred revenue on the accompanying condensed consolidated balance sheets and include payments received in advance of performance obligations under the contract and are realized when the associated revenue is recognized under the contract. Significant changes in the balances of contract liabilities (deferred revenues) and contract assets (prepaid expenses and other assets) during the period are as follows (in thousands): Contract Liabilities Balance on January 1, 2018 $ 116,830 Revenue recognized (36,283 ) Increase due to billings 25,533 Balance as of September 30, 2018 $ 106,080 Short-term contract liabilities (Deferred revenues) 32,015 Long-term contract liabilities (Deferred revenues) 74,065 Contract Assets Balance on January 1, 2018 $ 47,862 Amount recognized (11,741 ) Increase 9,722 Balance as of September 30, 2018 $ 45,843 Remaining Performance Obligations The following table includes estimated revenue expected to be recognized in future periods related to performance obligations that are unsatisfied or partially unsatisfied at the end of the reporting period (in thousands). September 30, 2018 (remaining 3 months) $ 8,922 2019 30,505 2020 24,352 2021 18,162 2022 13,112 Thereafter 11,027 Total $ 106,080 Practical Expedients and Exemptions The Company generally expenses sales commissions related to products delivered at a point in time when the commissions are incurred because the amortization period would have been less than one year. The Company records these costs as sales and marketing expense. The Company expenses shipping and handling costs as incurred. Impact of Adoption of Topic 606 In accordance with Topic 606, the disclosure of the impact of adoption to the Company’s condensed consolidated statements of operations and condensed consolidated balance sheets was as follows (in thousands): Three Months Ended Nine Months Ended As Reported Adjustments Without Adoption of Topic 606 As Reported Adjustments Without Adoption of Topic 606 Net revenues $ 78,002 $ 323 $ 77,679 $ 223,870 $ 2,781 $ 221,089 Cost of revenues 52,738 413 52,325 157,589 1,409 156,180 Gross profit 25,264 (90 ) 25,354 66,281 1,372 64,909 Operating expenses: — — Research and development 8,165 — 8,165 25,247 — 25,247 Sales and marketing 7,375 — 7,375 20,430 58 20,372 General and administrative 7,510 — 7,510 21,423 — 21,423 Restructuring charges 2,588 — 2,588 2,588 — 2,588 Total operating expenses 25,638 — 25,638 69,688 58 69,630 Loss from operations (374 ) (90 ) (284 ) (3,407 ) 1,314 (4,721 ) Other expense, net Interest expense (2,469 ) — (2,469 ) (7,031 ) — (7,031 ) Other expense (379 ) — (379 ) (1,077 ) — (1,077 ) Total other expense, net (2,848 ) — (2,848 ) (8,108 ) — (8,108 ) Loss before income taxes (3,222 ) (90 ) (3,132 ) (11,515 ) 1,314 (12,829 ) Income tax provision (248 ) — (248 ) (821 ) — (821 ) Net loss $ (3,470 ) $ (90 ) $ (3,380 ) $ (12,336 ) $ 1,314 $ (13,650 ) Net loss per share: Basic and diluted $ (0.03 ) $ — $ (0.03 ) $ (0.13 ) $ 0.01 $ (0.14 ) Shares used in per share calculation: Basic and diluted 102,798 — 102,798 97,257 — 97,257 September 30, 2018 As Reported Adjustments Without Adoption of Topic 606 Prepaid expenses and other $ 21,631 $ 9,465 $ 12,166 Other assets 35,520 28,450 7,070 Accrued liabilities 41,562 5,372 36,190 Deferred revenues 32,015 19,369 12,646 Deferred revenues, noncurrent 74,065 50,804 23,261 Accumulated deficit (347,011 ) (37,630 ) (309,381 )

INVENTORY

INVENTORY	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory as of September 30, 2018 and December 31, 2017 consists of the following (in thousands): September 30, December 31, Raw materials $ 1,467 $ 2,341 Finished goods 16,419 23,658 Total inventory $ 17,886 $ 25,999

WARRANTY OBLIGATIONS

WARRANTY OBLIGATIONS	9 Months Ended
	Sep. 30, 2018
Product Warranties Disclosures [Abstract]
WARRANTY OBLIGATIONS	WARRANTY OBLIGATIONS The Company’s warranty activities during the three and nine months ended September 30, 2018 and 2017 were as follows (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Warranty obligations, beginning of period $ 31,642 $ 31,613 $ 29,816 $ 31,414 Accruals for warranties issued during period 689 1,009 2,222 2,913 Changes in estimates 1,997 (1,046 ) 4,825 (826 ) Settlements (2,467 ) (1,494 ) (6,242 ) (5,092 ) Increase due to accretion expense 514 549 1,453 1,542 Other (191 ) (279 ) 110 401 Warranty obligations, end of period $ 32,184 $ 30,352 $ 32,184 $ 30,352 Less current portion $ (9,117 ) $ (7,151 ) Noncurrent $ 23,067 $ 23,201 As of September 30, 2018 , the $32.2 million of warranty obligations included $13.6 million measured at fair value. See Note 5 , “Fair Value Measurements” for additional information.

FAIR VALUE MEASUREMENTS

FAIR VALUE MEASUREMENTS	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENTS	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 recorded at fair value, the Company considers the principal or most advantageous market in which it would transact and considers assumptions that market participants would use when pricing the asset or liability, such as inherent risk, transfer restrictions, and risk of nonperformance. The fair value hierarchy requires an entity to maximize the use of observable inputs and minimize the use of unobservable inputs when measuring fair value. An asset’s or liability’s categorization within the fair value hierarchy is based upon the lowest level of input that is significant to the fair value measurement. Three levels of inputs may be used to measure fair value: • Level 1—Valuations based on quoted prices in active markets for identical assets or liabilities that the Company is able to access. Since valuations are based on quoted prices that are readily and regularly available in an active market, valuation of such assets or liabilities do not entail a significant degree of judgment. • Level 2—Valuations based on one or more quoted prices in markets that are not active or for which all significant inputs are observable, either directly or indirectly. • Level 3—Valuations based on inputs that are unobservable and significant to the overall fair value measurement. The following table presents the Company’s liabilities that were measured at fair value on a recurring basis and its categorization within the fair value hierarchy at September 30, 2018 and December 31, 2017 (in thousands): Fair Value September 30, December 31, Warranty obligations Level 3 $ 13,566 $ 9,790 Third party option to purchase receivables at a discount Level 3 — 700 Fair Value Option for Warranty Obligations Related to Microinverters Sold Since January 1, 2014 The Company’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 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 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 information regarding changes in nonfinancial liabilities related to the Company’s warranty obligations measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the periods indicated (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Balance at beginning of period $ 12,836 $ 12,564 $ 9,790 $ 10,332 Accruals for warranties issued during period 689 867 2,222 2,760 Changes in estimates 853 (1,452 ) 2,848 (2,051 ) Settlements (1,135 ) (530 ) (2,857 ) (1,265 ) Increase due to accretion expense 514 549 1,453 1,542 Other (191 ) (279 ) 110 401 Balance at end of period $ 13,566 $ 11,719 $ 13,566 $ 11,719 Quantitative and Qualitative Information about Level 3 Fair Value Measurements As of September 30, 2018 , 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 16% Credit-adjusted risk-free rate 16% As of December 31, 2017 , the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows: Item Measured at Fair Value Valuation Technique Description of Significant Unobservable Input Percent Used (Weighted-Average) Warranty obligations for microinverters sold since January 1, 2014 Discounted cash flows Profit element and risk premium 17% Credit-adjusted risk-free rate 17% Third party option to purchase receivables at a discount Discounted cash flows Counter party credit-adjusted risk-free rate 4% 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 (“discount rate”) is determined by reference to the Company’s own credit standing at the fair value measurement date. Increasing the profit element and risk premium input by 100 basis points would result in a $0.1 million increase to the liability. Decreasing the profit element and risk premium by 100 basis points would result in a $0.1 million reduction of the liability. Increasing the discount rate by 100 basis points would result in a $0.6 million reduction of the liability. Decreasing the discount rate by 100 basis points would result in a $0.6 million increase to the liability.

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
GOODWILL AND INTANGIBLE ASSETS	GOODWILL AND INTANGIBLE ASSETS The following table presents the details of the Company’s goodwill and purchased intangible assets as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Gross Additions Accumulated Amortization Net Gross Accumulated Amortization Net Goodwill $ 3,664 $ 21,119 $ — $ 24,783 $ 3,664 $ — $ 3,664 Intangible assets: Other indefinite-lived intangibles $ 286 $ — $ — $ 286 $ 286 $ — $ 286 Intangible assets with finite lives: Patents and licensed technology 1,665 — (1,665 ) — 1,665 (1,436 ) 229 Developed technology — 13,100 (408 ) 12,692 — — — Customer relationships — 23,100 — 23,100 — — — Total purchased intangible assets $ 1,951 $ 36,200 $ (2,073 ) $ 36,078 $ 1,951 $ (1,436 ) $ 515 In July 2014, the Company purchased certain patents related to system interconnection and photovoltaic AC module construction. The patents were amortized over their legal life of 3 years . In October 2015, the Company licensed certain technology related to ASIC development for a 3 year term, which is also its estimated useful life. As of September 30, 2018 , these patents were fully amortized. In August 2018, the Company acquired certain finite-lived intangible assets in its acquisition of SunPower Corporation ’s (" SunPower ") microinverter business pursuant to an Asset Purchase Agreement ("APA"), primarily developed technology and customer relationships. See Note 14 . “ Acquisition ” for additional information related to this acquisition. For the three and nine months ended September 30, 2018 and September 30, 2017 , amortization expense related to finite-lived intangible assets was $0.5 million , $0.6 million , $0.1 million and $0.4 million , respectively.

RESTRUCTURING

RESTRUCTURING	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
RESTRUCTURING	RESTRUCTURING 2018 Plan In the third quarter of 2018, the Company began implementing restructuring actions (the “2018 Plan”) to lower its operating expenses. The restructuring actions include reorganization of the Company’s global workforce, elimination of certain non-core projects and consolidation of facilities. The Company expects to complete this restructuring in 2019. The following table presents the details of the Company’s restructuring charges under the 2018 Plan for the periods indicated (in thousands): Three Months Ended Nine Months Ended Redundancy and employee severance and benefit arrangements $ 613 $ 613 Asset impairments 1,636 1,636 Lease loss reserves 339 339 Total restructuring $ 2,588 $ 2,588 The following table provides information regarding changes in the Company’s 2018 Plan accrued restructuring balance for the periods indicated (in thousands): Redundancy and Employee Severance and Benefits Lease Loss Reserves and Contractual Obligations Total Charges $ 613 $ 339 $ 952 Cash payments (297 ) — (297 ) Non-cash settlement and other — 10 10 Balance as of September 30, 2018 $ 316 $ 349 $ 665 2016 Plan In the third quarter of 2016, the Company began implementing restructuring actions (the “2016 Plan”) to lower its operating expenses. The restructuring actions have included reductions in the Company’s global workforce, the elimination of certain non-core projects, consolidation of office space at the Company’s corporate headquarters and the engagement of management consultants to assist the Company in making organizational and structural changes to improve operational efficiencies and reduce expenses. The Company substantially completed its restructuring activities in 2017. The following table presents the details of the Company’s restructuring charges under the 2016 Plan for the periods indicated (in thousands): Three Months Ended Nine Months Ended Employee severance and benefit arrangements $ 1,111 $ 2,826 Asset impairments — 522 Consultants engaged in restructuring activities 3,100 10,100 Lease loss reserves and contract termination costs (140 ) 1,479 Total restructuring $ 4,071 $ 14,927 The following table provides information regarding changes in the Company’s 2016 Plan accrued restructuring balance for the periods indicated (in thousands): Employee Severance and Benefits Lease Loss Reserves and Contractual Obligations Total Balance as of December 31, 2017 $ 229 $ 1,094 $ 1,323 Cash payments and receipts, net (229 ) 707 478 Non-cash settlement — — — Balance as of September 30, 2018 $ 0 $ 1,801 $ 1,801

DEBT

DEBT	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
DEBT	DEBT Long-term debt was comprised of the following at September 30, 2018 and December 31, 2017 (in thousands): September 30, December 31, Convertible Notes due 2023 $ 65,000 $ — Less unamortized issuance costs (2,492 ) — Carrying amount of Convertible Notes due 2023 62,508 — Term loan 44,336 50,000 Less unamortized discount and issuance costs (1,299 ) (2,111 ) Carrying amount of term loan 43,037 47,889 Sale of long term financing receivable recorded as debt 6,487 2,562 Less value of future purchase option — (700 ) Carrying amount of sale of long term financing receivable recorded as debt 6,487 1,862 Total carrying amount of debt 112,032 49,751 Less current portion term loan (21,387 ) (15,715 ) Less current portion of long term financing receivable recorded as debt (2,738 ) (1,714 ) Long-term debt $ 87,907 $ 32,322 Convertible Notes In August 2018 , the Company sold $60.0 million aggregate principal amount of convertible senior notes due 2023 (the “Convertible Notes”) in a private placement. Additionally, an individual who is a member of the Company’s Board of Directors and a stockholder, Thurman John Rodgers, purchased $5.0 million aggregate principal amount of convertible senior notes due 2023 (the “Affiliate Notes” and together with the Convertible Notes, the “Notes”) in a concurrent private placement. The Company received net proceeds of $62.4 million , after deducting the underwriters’ fees of approximately $2.0 million and other issuance costs of approximately $0.6 million . The Notes are senior, unsecured and bear interest at a rate of 4.0% per year, payable semi-annually on February 1 and August 1 of each year, beginning on February 1, 2019 . The Notes will mature on August 1, 2023 , unless earlier repurchased by the Company or converted at the option of the holders. The Company may not redeem the Notes prior to the maturity date, and no sinking fund is provided for the Notes. The Notes are convertible, at a holder’s election, in multiples of $1,000 principal amount, into shares of the Company’s common stock, based on the applicable conversion rate. The initial conversion rate for the Notes is 180.0180 shares of common stock per $1,000 principal amount of Notes (which is equivalent to an initial conversion price of approximately $5.5600 per share ). The conversion rate and the corresponding conversion price are subject to adjustment upon the occurrence of certain events, but will not be adjusted for any accrued and unpaid interest. Holders of the Notes who convert their Notes in connection with a make-whole fundamental change (as defined in the Indenture) are, under certain circumstances, entitled to an increase in the conversion rate. Additionally, in the event of a fundamental change, holders of the Notes may require the Company to repurchase all or a portion of their Notes at a price equal to 100% of the principal amount of Notes, plus any accrued and unpaid interest, including any additional interest to, but excluding, the repurchase date. Holders may convert all or any portion of their Notes at their option at any time prior to the close of business on the business day immediately preceding the maturity date, in multiples of $1,000 principal amount. As of September 30, 2018 , there were unamortized issuance costs and debt discounts of approximately $2.5 million , which were recorded as a direct deduction from the Notes on the condensed consolidated balance sheets. Term Loan In July 2016, the Company entered into a Loan and Security Agreement (the “Original Term Loan Agreement”) with lenders that are affiliates of Tennenbaum Capital Partners, LLC (the “Lenders” or “TCP”). Under the agreement, the Lenders committed to advance a term loan in an aggregate principal amount of up to $25.0 million with a maturity date of July 1, 2020. The Company borrowed the entire $25.0 million of term loan commitments on the loan closing date. Monthly payments due through June 30, 2017 were interest only, followed by consecutive equal monthly payments of principal plus accrued interest that were to begin on July 1, 2017 and continue through the maturity date. The term loan provided for an interest rate per annum equal to the higher of (i) 10.25% or (ii) LIBOR plus 9.5625% , subject to a 1.0% reduction if the Company achieves minimum levels of Revenue and EBITDA (each as defined in the Original Term Loan Agreement) for the twelve-consecutive month period ending June 30, 2017 as set forth in the Original Term Loan Agreement. In addition, the Company paid a commitment fee of 3.3% of the loan amount upon closing and a closing fee of 10.0% of the loan amount is payable in four equal installments at each anniversary of the closing date. The Company could elect to prepay the loan by incurring a prepayment fee between 1% and 3% of the principal amount of the term loan depending on the timing and circumstances of prepayment. In February 2017, the Company entered into an Amended and Restated Loan and Security Agreement (the “Loan Agreement”) that amended and restated the Original Term Loan Agreement. The Loan Agreement provides for a $25.0 million secured term loan to the Company (the “New Term Loan”), which is in addition to the $25.0 million secured term loan borrowed by the Company under the Original Term Loan Agreement (together with the “New Term Loan” the “Term Loans”). The New Term Loan has the same July 1, 2020 maturity date that was applicable to the Original Term Loan Agreement. The New Term Loan was fully drawn at closing, with approximately $10.3 million of the proceeds used to repay existing combined principal and interest due under the Company’s Revolver with Wells Fargo. Upon the repayment of loans under the Wells Fargo Revolver, the Wells Fargo Revolving Credit Agreement was terminated. The Company used the remainder of the proceeds from the New Term Loan for general corporate purposes. Monthly payments under the Term Loans through February 28, 2018 are interest only, followed by consecutive equal monthly payments of principal plus accrued interest beginning on March 1, 2018 and continuing through the maturity date. Interest on the Term Loans is the greater of (a) 10.3125% , and (b) a fluctuating rate of interest per annum equal to the three-month LIBOR Rate (rounded up to the nearest 1/16th of one percent) plus 9.25% . In addition, the Company paid a commitment fee of 3.0% of the New Term Loan amount upon closing and a closing fee of 4.0% of the New Term Loan amount, which is payable with the closing fee under the Original Term Loan Agreement in four equal installments at each anniversary of the closing date of the Original Term Loan Agreement. The Company may elect to prepay the Term Loans by incurring a prepayment fee between 1% and 3% of the principal amount of the Term Loans depending on the timing and circumstances of prepayment. On February 28, 2018, the Company entered into a Second Amendment to the Term Loans. The Second Amendment decreased by 50% the amount of principal repayments required under the Loan Agreement for the period from March 1, 2018 through December 31, 2018 and provided that the Company shall not prepay any part of the Term Loans during that same period without the Collateral Agent’s prior written consent. The Term Loans are secured by a first-priority security interest on substantially all assets of the Company; provided, however, that the security interest in the Company’s intellectual property may be released if the Company satisfies certain requirements. The Company’s obligations under the Term Loans are not guaranteed by any of the Company’s existing subsidiaries, nor have any existing subsidiaries of the Company pledged any of their assets to secure the Term Loans. The Loan Agreement requires that (i) at all times from the closing date to and including March 31, 2018, the Company, and any future guarantors, have Unrestricted Cash (as defined in the Loan Agreement) of at least $10.0 million ; (ii) at all times from the closing date to and including March 31, 2018, that the aggregate amount of Consolidated Unrestricted Cash, plus the value of Consolidated Receivables, plus the value of Consolidated Inventory (each as defined in the Loan Agreement) divided by the outstanding principal amount of Term Loans, shall equal or exceed 1.5 ; and (iii) at all times from April 1, 2018 and thereafter, that the aggregate amount of Consolidated Unrestricted Cash, plus the value of Consolidated Receivables, plus the value of Consolidated Inventory divided by the outstanding principal amount of Term Loans, shall equal or exceed 1.75 . In addition, the Loan Agreement is subject to customary affirmative and negative covenants including restrictions on creation of liens, dispositions of assets, mergers, changing the nature of its business and dividends and other distributions, in each case subject to certain exceptions. The Loan Agreement also contains certain customary events of default including, but not limited to, failure to pay interest, principal and fees or other amounts when due, material breach of any representation or warranty, covenant defaults, cross defaults to other material indebtedness, events of bankruptcy and the occurrence of a material adverse change (as defined in the agreement) to the Company’s business. The Term Loan Agreement offers TCP customary rights and remedies in any event of default, including the ability to declare all amounts outstanding immediately due and payable. In connection with the New Term Loan, the Company issued to the Lenders warrants to purchase an aggregate 1,220,000 shares of the Company’s Common Stock at an exercise price of $1.05 per share. The warrants have a term of seven years and contain a “cashless exercise” feature that allows the holder to exercise the warrant without a cash payment upon the terms set forth therein. The Company estimated the fair value of the warrants by using the Black-Scholes approach and the following assumptions: stock price of $1.56 ; strike price of $1.05 ; volatility of 85.9% , risk-free rate of 2.23% ; dividend yield of 0% ; and a 7 year term. The resulting fair value was used to allocate the proceeds from the Term Loan between liability and equity components. The Company classified the warrants as equity and allocated the proceeds from the Term Loan and warrants using the relative fair value method. Using this method, the Company allocated $1.4 million to the warrants, which was recorded as equity. This amount represents debt discount that will be amortized to interest expense over the term of the loan. The Lenders converted the warrants into 912,067 shares of the Company’s common stock in a cashless exercise in the first quarter of 2018. As of September 30, 2018 , the estimated schedule of principal payments due on the term loan is as follows (in thousands): Year Amounts 2018 (remaining 3 months) $ 2,545 2019 25,497 2020 16,294 Total $ 44,336 Sale of Long Term Financing Receivables The Company entered into an agreement with a third party in the fourth quarter of 2017 to sell certain current and future receivables at a discount. In December 2017, the third party made an initial purchase of receivables that resulted in net proceeds to the Company of $2.8 million . This transaction was recorded as debt on the accompanying consolidated balance sheets, and the debt balance will be relieved by January 2019 as the underlying receivables are settled. During the nine months ended September 30, 2018 , the third party made three additional purchases of receivables that resulted in total net proceeds to the Company of $5.6 million . These transactions were recorded as debt on the accompanying condensed consolidated balance sheets, and the total associated debt balance will be relieved by September 2021 as the underlying receivables are settled. After the initial purchase, the buyer had the option to purchase certain additional future receivables at various fixed discounts. This option was valued at $0.7 million and was recorded as a liability with a corresponding offset to debt as of December 31, 2017. As of September 30, 2018 , all purchases relating to this option had been made, and the liability has been relieved. See Note 5, “Fair Value Measurements” for additional information. Revolving Credit Facility The Company had a $50.0 million revolving credit facility with Wells Fargo Bank, N.A. (“Wells Fargo”) that was entered into in November 2012. The Revolver had a balance of $10.1 million as of December 31, 2016 and was fully repaid and terminated in February 2017.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	9 Months Ended
	Sep. 30, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND 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. The Company was previously involved in a dispute with a supplier regarding purchase volume commitments for which the Company recorded a liability of $1.8 million in the first quarter of 2018. The matter was resolved in the second quarter of 2018 for approximately $1.8 million . On April 12, 2018 , the Company entered into a lease agreement for its corporate headquarters in Fremont, California. This lease commenced on September 1, 2018 and has a term of approximately 5 years with a five year renewal option. As of September 30, 2018 , $2.2 million remain on this facility lease obligation. On August 9, 2018 , the Company completed the acquisition of SunPower ’s microinverter business pursuant to an APA by which the Company acquired certain assets and liabilities of SunPower relating to the research and development and manufacturing of microinverters. Pursuant to the APA, the Company will make an additional cash payment of $10.0 million to SunPower on the earlier of the 4 month anniversary of the Closing and December 28, 2018 . See Note 14 , “ Acquisition ,” for additional information related to this acquisition.

SALE OF COMMON STOCK

SALE OF COMMON STOCK	9 Months Ended
	Sep. 30, 2018
Equity [Abstract]
SALE OF COMMON STOCK	SALE OF COMMON STOCK On February 4, 2018, the Company entered into a Securities Purchase Agreement with an investor pursuant to which the Company, in a private placement, issued and sold to the investor 9,523,809 shares of the Company’s common stock at a price per share of $2.10 , for gross proceeds of $20.0 million .

STOCK-BASED COMPENSATION

STOCK-BASED COMPENSATION	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK-BASED COMPENSATION	STOCK-BASED COMPENSATION The Company has adopted certain equity incentive and stock purchase plans as described in the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 . Equity Awards Activity Stock Options The following is a summary of stock option activity for the nine months ended September 30, 2018 (in thousands, except per share data): Number of Weighted- Outstanding at December 31, 2017 8,426 $ 1.77 Granted 213 4.43 Exercised (1,185 ) 1.70 Canceled (292 ) 3.59 Outstanding at September 30, 2018 7,162 1.78 Vested and expected to vest at September 30, 2018 6,727 1.80 Exercisable at September 30, 2018 4,572 1.90 The intrinsic value of options exercised in the nine months ended September 30, 2018 was $4.6 million . As of September 30, 2018 , the intrinsic value of options outstanding was $23.4 million based on the closing price of the Company’s stock as of September 30, 2018 . Restricted Stock Units and Performance Stock Units The following is a summary of restricted stock unit (“RSU”) and performance stock unit (“PSU”) activity for the nine months ended September 30, 2018 (in thousands, except per share data): Number of Weighted Average Outstanding at December 31, 2017 3,505 $ 2.03 Granted 4,126 3.67 Vested (1,060 ) 2.63 Canceled (825 ) 1.91 Outstanding at September 30, 2018 5,746 3.11 Expected to vest at September 30, 2018 4,791 3.08 The total intrinsic value of RSUs and PSUs that vested in the nine months ended September 30, 2018 was $4.8 million . As of September 30, 2018 , the intrinsic value of RSUs and PSUs outstanding was $27.9 million based on the closing price of the Company’s stock as of September 30, 2018 . Stock-based compensation expense is measured at the grant date based on the fair value of the award. During the second quarter of 2018 the Company issued a PSU grant of 1.4 million shares, of which 720 thousand shares include market conditions. Each grantee is granted a target award of PSUs and may earn between 0% and 150% of the target award depending on the Company’s performance against the performance goals. For PSUs, the grant date fair value is recognized as expense when the performance condition is probable of being achieved, and then on a graded basis over the requisite service period. The fair value of awards containing market conditions was determined using a Monte Carlo simulation model based upon the terms of the conditions, the expected volatility of the underlying security, and other relevant factors. The weighted average estimated fair value of the PSUs without market conditions was $4.57 per share, and the weighted average estimated fair value of the PSUs with market conditions was $4.54 per share. During the three months ended September 30, 2018 , no RSU or PSU shares were granted. On April 3, 2017, the Company commenced a Tender Offer (the “Offer”) to exchange out of the money stock options for restricted stock units. The Offer expired on Monday, May 1, 2017. Pursuant to the Offer, the Company accepted elections to exchange options to purchase 2,362,470 shares of common stock and issued replacement awards of RSUs for 733,559 shares of common stock. As the transaction approximated a value-for-value exchange, it did not have a material impact on the Company’s stock-based compensation expense. Stock-based Compensation Expense Compensation expense 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 condensed consolidated statements of operations for the periods presented (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Cost of revenues $ 330 $ 347 $ 945 $ 796 Research and development 878 607 2,645 1,994 Sales and marketing 1,151 226 2,509 889 General and administrative 1,692 547 3,812 1,598 Total $ 4,051 $ 1,727 $ 9,911 $ 5,277 The following table summarizes the various types of stock-based compensation expense for the periods presented (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Stock options and RSUs and PSUs $ 3,708 $ 1,473 $ 9,001 $ 4,363 Employee stock purchase plan 343 254 910 914 Total $ 4,051 $ 1,727 $ 9,911 $ 5,277 The following table presents the weighted-average grant date fair value of options granted for the periods presented and the assumptions used to estimate those values using a Black-Scholes option pricing model: Three Months Ended Nine Months Ended 2018 2017 2018 2017 Weighted average grant date fair value ** $ 0.69 $ 2.83 $ 0.70 Expected term (in years) ** 4.2 4.0 4.4 Expected volatility ** 83.8 % 88.5 % 84.4 % Annual risk-free rate of return ** 1.6 % 2.6 % 1.8 % Dividend yield ** 0.0 % 0.0 % 0.0 % ** No options were granted during the three months ended September 30, 2018 . As of September 30, 2018 , there was approximately $16.3 million of total unrecognized compensation expense related to unvested equity awards expected to be recognized over a weighted-average period of 2.4 years .

INCOME TAXES

INCOME TAXES	9 Months Ended
	Sep. 30, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The Company used the discrete tax approach in calculating the tax expense for the three and nine months ended September 30, 2018 and 2017 due to the fact that a relatively small change in the Company’s projected pre-tax net income (loss) could result in a volatile effective tax rate. Under the discrete method, the Company determines its tax (expense) benefit based upon actual results as if the interim period was an annual period. The tax provision recorded was primarily related to income taxes attributable to its foreign operations.

NET LOSS PER SHARE

NET LOSS PER SHARE	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
NET LOSS PER SHARE	NET LOSS PER SHARE Basic net loss per share is computed by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Diluted loss per share is computed in a similar manner, but it also includes the effect of potential common shares outstanding during the period, when dilutive. Potential common shares include outstanding in-the-money stock options, restricted stock units, shares to be purchased under the Company’s employee stock purchase plan, warrants to purchase common stock, and the Notes. The dilutive effect of potentially dilutive common shares is reflected in diluted earnings per share by application of the treasury stock method. To the extent these potential common shares are antidilutive, they are excluded from the calculation of diluted net loss per share. The following table presents the computation of basic and diluted net loss per share for the periods presented (in thousands, except per share data): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Numerator: Net loss $ (3,470 ) $ (6,854 ) $ (12,336 ) $ (42,252 ) Denominator: Weighted average common shares outstanding 102,798 84,862 97,257 81,993 Net loss per share, basic and diluted $ (0.03 ) $ (0.08 ) $ (0.13 ) $ (0.52 ) As the Company incurred a net loss for all periods presented, potential dilutive securities from employee stock options, restricted stock units, warrants, and convertible notes have been excluded from the diluted net loss per share computations because the effect of including such shares would have been anti-dilutive. The following outstanding shares of common stock equivalents were excluded from the calculation of the diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Employee stock options 7,404 7,844 7,971 8,121 RSUs and PSUs 5,924 3,306 5,106 1,959 Warrants to purchase common stock — 1,220 — 1,033 Total 13,328 12,370 13,077 11,113 The conversion of the Notes will have a dilutive impact when the average market price of the Company’s common stock for a given period exceeds the conversion price of $5.56 per share. The Notes are convertible at the holder’s option at 180.0180 shares per $1,000 note.

ACQUISITION

ACQUISITION	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
ACQUISITION	On August 9, 2018 , the Company completed its acquisition of SunPower ’s microinverter business pursuant to an APA by which the Company acquired certain assets and liabilities of SunPower relating to the research and development and manufacturing of microinverters. The acquisition was accounted for as a business combination and, accordingly, the total purchase price was allocated to the preliminary net tangible and intangible assets and liabilities based on their preliminary fair values on the acquisition date. In conjunction with the APA, the Company entered into a Master Supply Agreement (“MSA”) with SunPower. Pursuant to the terms of the MSA, the Company becomes the exclusive supplier of Module Level Power Electronics (“MLPEs”) for SunPower ’s Residential Business in U.S for a period of five years . The resulting customer relationship intangible is accounted for as a distinct transaction from the acquired business. The acquisition date fair value of the consideration transferred was approximately $57.3 million , which consisted of the following (in thousands): Cash consideration $ 25,000 Common stock issued 32,319 Total $ 57,319 On the closing date, the Company paid $15.0 million of cash purchase price to SunPower. In addition, $10.0 million of the cash purchase price is to be paid to SunPower on December 10, 2018 and is included as part of accrued liabilities on the Company’s condensed consolidated balance sheet as of September 30, 2018. The fair value of the Company’s 7.5 million shares of common stock issued, valued at $32.3 million , was determined based on the closing market price of the Company’s common stock on the acquisition date, less a discount of 14% to 30% (depending on the year) for lack of marketability as the shares issued are subject to a restriction that limits their trade or transfer with a lock-up period of six months and restrictions on the number of shares that can be transferred by SunPower in each six -month period following the lock-up period. The following table summarizes the preliminary estimated fair values of the assets acquired and liabilities assumed at the acquisition date (in thousands): Intangible assets $ 36,200 Goodwill 21,119 Net assets acquired $ 57,319 The excess of the consideration paid over the fair values assigned to the assets acquired and liabilities assumed represents the goodwill resulting from the acquisition. The $21.1 million of goodwill recognized is attributable primarily to the benefits the Company expects to derive from enhanced scale and efficiency to better serve its markets. Goodwill is expected to be deductible over the next 15 years for income tax purposes. The fair values assigned to tangible and identifiable intangible assets acquired are based on management’s estimates and assumptions. The fair values of assets acquired are preliminary and may be subject to change within the measurement period as the fair value assessments are finalized. The following table shows the fair value of the separately identifiable intangible assets at the time of acquisition and the period over which each intangible asset will be amortized: Preliminary fair value (in thousands) Useful life (in years) Developed technology $ 13,100 6 Customer relationship 23,100 9 Total identifiable intangible assets $ 36,200 The developed technology acquired is embedded in the microinverters that SunPower sells to its customers. The Company already has developed microinverter technology and the Company will supply its microinverters to SunPower through the term of the MSA. The Company does not intend to actively use the developed technology acquired from SunPower, but does plan to hold the developed technology to prevent other potential competitors from obtaining access to the technology, therefore the Company will account for the developed technology as a defensive intangible asset. The Company expects to realize the benefits of the developed technology over the period of time in which the Company will supply microinverters to SunPower. The Company does expect changes in microinverter technology during the life of the customer relationship with SunPower and expects to benefit from preventing competitors access to the technology over a period of six years , therefore, the Company will amortize the value of the developed technology intangible asset over a period of six years . The SunPower microinverter business' contributions to revenue and income for the period from the date of acquisition to September 30, 2018 were not material. The MSA was negotiated together with the APA and provides the Company with the exclusive right to supply SunPower with MLPEs for a period of five years , with options for renewals. The exclusivity arrangement extends throughout the term of the MSA, which comprises all of the expected cash flows from the customer relationship intangible asset, and was a condition to, and was an essential part of the acquisition of the microinverter business by the Company. As the fair value ascribed to the customer relationship intangible asset represents payments to a customer, the Company will amortize the value of the customer relationship intangible asset as a reduction to revenue using a pattern of economic benefit method over a useful life of nine years . The table below shows estimated fair values of the assets acquired funded by cash and issuance of common stock at the acquisition date (in thousands): Cash Purchase Price Issuance of Common Stock Total Consideration % of Total Consideration Developed technology and goodwill $ 15,000 $ 19,219 $ 34,219 60 % Customer relationship 10,000 13,100 23,100 40 % Total consideration $ 25,000 $ 32,319 $ 57,319 100 % The Company allocated $6.0 million of the $15.0 million paid of the cash purchase price to cash flows from operating activities and the remaining $9.0 million to cash used in investing activities in the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 . The allocation was based on the valuation of the customer relationship relative to the overall consideration. In addition, the Company disclosed $19.2 million from issuance of common stock and $6.0 million of cash purchase price accrued to be paid for the developed technology and goodwill as non-cash investing activities in the condensed consolidated statements of cash flows for the nine months ended September 30, 2018 . Total acquisition related costs were approximately $0.8 million , which were included in general and administrative expenses. The Company determined it is impractical to include such pro forma information given the difficulty in obtaining the historical financial information for the SunPower microinverter business as the business was part of SunPower and did not have discrete financial information prior to the acquisition. Inclusion of such information would require the Company to make estimates and assumptions regarding the acquired business's historical financial results that the Company believes may ultimately prove inaccurate.

DESCRIPTION OF BUSINESS AND B_2

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Policies)	9 Months Ended
	Sep. 30, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The accompanying condensed consolidated financial statements are presented in accordance with accounting principles generally accepted in the U.S, or GAAP. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany balances and transactions have been eliminated in consolidation.
Unaudited Interim Financial Information	Unaudited Interim Financial Information These accompanying unaudited condensed consolidated financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the “SEC”) for interim financial reporting. In the opinion of management, these unaudited condensed consolidated financial statements reflect all adjustments, consisting of normal recurring items, considered necessary to present fairly the Company's financial condition, results of operations, comprehensive loss and cash flows for the interim periods indicated. The results of operations for the three and nine months ended September 30, 2018 are not necessarily indicative of the operating results for the full year. Certain information and footnote disclosures typically included in annual consolidated financial statements have been condensed or omitted. Accordingly, these unaudited interim condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 .
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with 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. Significant estimates and assumptions reflected in the financial statements include revenue recognition, inventory valuation and accrued warranty obligations. 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.
Recently Adopted Accounting Pronouncements and Recently Issued Accounting Pronouncements Not Yet Effective	Recently Adopted Accounting Pronouncements In May 2014, the FASB issued Accounting Standards Update No. (“ASU”) 2014-09, “Revenue from Contracts with Customers,” amending revenue recognition guidance and requiring more detailed disclosures to enable users of financial statements to understand the nature, amount, timing, and uncertainty of revenue and cash flows arising from contracts with customers. The amended guidance, herein referred to as Topic 606, is effective for annual and interim reporting periods beginning after December 15, 2017, with early adoption permitted for public companies effective for annual and interim reporting periods beginning after December 15, 2016. The Company has adopted Topic 606 effective January 1, 2018, using the modified retrospective transition method. The Company recognized the cumulative effect of applying the new revenue standard as an adjustment to the opening balance of retained earnings on January 1, 2018. The comparative information has not been restated and continues to be reported under the accounting standards in effect for the period presented. See Note 2, “Revenue Recognition,” for additional accounting policy and transition disclosures. 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 was 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 standard, which was adopted in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. In November 2016, the FASB issued ASU 2016-18, “Statement of Cash Flows,” which requires companies to include amounts generally described as restricted cash and restricted cash equivalents in cash and cash equivalents when reconciling beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The standard, which was adopted prospectively in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. In May 2017, the FASB issued ASU 2017-09, "Compensation - Stock Compensation." ASU 2017-09 was issued to provide clarity and reduce both 1) diversity in practice and 2) cost and complexity when applying the guidance in Topic 718 to a change in the terms or conditions of a share-based payment award. ASU 2017-09 provides guidance about which changes to the terms or conditions of a share-based payment award require an entity to apply modification accounting under Topic 718. ASU 2017-09 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. The standard, which was adopted in the first quarter of 2018, did not have a material impact on the condensed consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Effective In February 2016, the FASB issued ASU 2016-02, Leases (“ASU 2016-02”). The guidance will require lessees to recognize all leases, with certain exceptions, on their balance sheets, whether operating or financing, while continuing to recognize the expenses on their income statements in a manner similar to current practice. The guidance states that a lessee would recognize a lease liability for the obligation to make lease payments and a right-to-use asset for the right to use the underlying asset for the lease term. The guidance will be effective for the Company beginning January 1, 2019 and early adoption is permitted. The Company will adopt ASU 2016-02 on January 1, 2019 and intends to elect the available practical expedients upon adoption. Upon adoption, the Company expects the consolidated balance sheet to include a right of use asset and a corresponding lease liability related to substantially all of the Company’s lease arrangements. The Company is evaluating the accounting, transition and disclosure requirements of the standard.
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 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.
Options for Warranty Obligations	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 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 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.
Commitments and 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.
Income Taxes	The Company used the discrete tax approach in calculating the tax expense for the three and nine months ended September 30, 2018 and 2017 due to the fact that a relatively small change in the Company’s projected pre-tax net income (loss) could result in a volatile effective tax rate. Under the discrete method, the Company determines its tax (expense) benefit based upon actual results as if the interim period was an annual period.
Earnings Per Share	Basic net loss per share is computed by dividing net loss by the weighted average number of shares of common stock outstanding during the period. Diluted loss per share is computed in a similar manner, but it also includes the effect of potential common shares outstanding during the period, when dilutive. Potential common shares include outstanding in-the-money stock options, restricted stock units, shares to be purchased under the Company’s employee stock purchase plan, warrants to purchase common stock, and the Notes. The dilutive effect of potentially dilutive common shares is reflected in diluted earnings per share by application of the treasury stock method. To the extent these potential common shares are antidilutive, they are excluded from the calculation of diluted net loss per share.

REVENUE RECOGNITION (Tables)

REVENUE RECOGNITION (Tables)	9 Months Ended
	Sep. 30, 2018
Revenue from Contract with Customer [Abstract]
Summary of Revenue Disaggregation	The following table provides information about disaggregated revenue by primary geographical market and timing of revenue recognition for the Company’s single product line (in thousands): Three Months Ended Nine Months Ended Primary geographical markets: United States $ 54,880 $ 148,268 International 23,122 75,602 Total $ 78,002 $ 223,870 Timing of revenue recognition: Products transferred at a point in time $ 68,256 $ 193,564 Products and services transferred over time 9,746 30,306 Total $ 78,002 $ 223,870
Summary of Contract Assets and Contract Liabilities, and Changes in Balances from Contracts with Customers	As of September 30, 2018 , receivables, contract assets and contract liabilities from contracts with customers consist of the following (in thousands): September 30, 2018 Receivables $ 54,117 Short-term contract assets (Prepaid expenses and other assets) 12,876 Long-term contract assets (Other assets) 32,967 Short-term contract liabilities (Deferred revenues) 32,015 Long-term contract liabilities (Deferred revenues) 74,065 Significant changes in the balances of contract liabilities (deferred revenues) and contract assets (prepaid expenses and other assets) during the period are as follows (in thousands): Contract Liabilities Balance on January 1, 2018 $ 116,830 Revenue recognized (36,283 ) Increase due to billings 25,533 Balance as of September 30, 2018 $ 106,080 Short-term contract liabilities (Deferred revenues) 32,015 Long-term contract liabilities (Deferred revenues) 74,065 Contract Assets Balance on January 1, 2018 $ 47,862 Amount recognized (11,741 ) Increase 9,722 Balance as of September 30, 2018 $ 45,843
Summary of Estimated Revenue Expected to be Recognized in Future Periods	The following table includes estimated revenue expected to be recognized in future periods related to performance obligations that are unsatisfied or partially unsatisfied at the end of the reporting period (in thousands). September 30, 2018 (remaining 3 months) $ 8,922 2019 30,505 2020 24,352 2021 18,162 2022 13,112 Thereafter 11,027 Total $ 106,080
Summary of New Accounting Adoption Impact on Consolidated Statements of Income and Condensed Consolidated Balance Sheets	In accordance with Topic 606, the disclosure of the impact of adoption to the Company’s condensed consolidated statements of operations and condensed consolidated balance sheets was as follows (in thousands): Three Months Ended Nine Months Ended As Reported Adjustments Without Adoption of Topic 606 As Reported Adjustments Without Adoption of Topic 606 Net revenues $ 78,002 $ 323 $ 77,679 $ 223,870 $ 2,781 $ 221,089 Cost of revenues 52,738 413 52,325 157,589 1,409 156,180 Gross profit 25,264 (90 ) 25,354 66,281 1,372 64,909 Operating expenses: — — Research and development 8,165 — 8,165 25,247 — 25,247 Sales and marketing 7,375 — 7,375 20,430 58 20,372 General and administrative 7,510 — 7,510 21,423 — 21,423 Restructuring charges 2,588 — 2,588 2,588 — 2,588 Total operating expenses 25,638 — 25,638 69,688 58 69,630 Loss from operations (374 ) (90 ) (284 ) (3,407 ) 1,314 (4,721 ) Other expense, net Interest expense (2,469 ) — (2,469 ) (7,031 ) — (7,031 ) Other expense (379 ) — (379 ) (1,077 ) — (1,077 ) Total other expense, net (2,848 ) — (2,848 ) (8,108 ) — (8,108 ) Loss before income taxes (3,222 ) (90 ) (3,132 ) (11,515 ) 1,314 (12,829 ) Income tax provision (248 ) — (248 ) (821 ) — (821 ) Net loss $ (3,470 ) $ (90 ) $ (3,380 ) $ (12,336 ) $ 1,314 $ (13,650 ) Net loss per share: Basic and diluted $ (0.03 ) $ — $ (0.03 ) $ (0.13 ) $ 0.01 $ (0.14 ) Shares used in per share calculation: Basic and diluted 102,798 — 102,798 97,257 — 97,257 September 30, 2018 As Reported Adjustments Without Adoption of Topic 606 Prepaid expenses and other $ 21,631 $ 9,465 $ 12,166 Other assets 35,520 28,450 7,070 Accrued liabilities 41,562 5,372 36,190 Deferred revenues 32,015 19,369 12,646 Deferred revenues, noncurrent 74,065 50,804 23,261 Accumulated deficit (347,011 ) (37,630 ) (309,381 )

INVENTORY (Tables)

INVENTORY (Tables)	9 Months Ended
	Sep. 30, 2018
Inventory Disclosure [Abstract]
Summary of Inventory	Inventory as of September 30, 2018 and December 31, 2017 consists of the following (in thousands): September 30, December 31, Raw materials $ 1,467 $ 2,341 Finished goods 16,419 23,658 Total inventory $ 17,886 $ 25,999

WARRANTY OBLIGATIONS (Tables)

WARRANTY OBLIGATIONS (Tables)	9 Months Ended
	Sep. 30, 2018
Product Warranties Disclosures [Abstract]
Summary of Warranty Activities	The Company’s warranty activities during the three and nine months ended September 30, 2018 and 2017 were as follows (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Warranty obligations, beginning of period $ 31,642 $ 31,613 $ 29,816 $ 31,414 Accruals for warranties issued during period 689 1,009 2,222 2,913 Changes in estimates 1,997 (1,046 ) 4,825 (826 ) Settlements (2,467 ) (1,494 ) (6,242 ) (5,092 ) Increase due to accretion expense 514 549 1,453 1,542 Other (191 ) (279 ) 110 401 Warranty obligations, end of period $ 32,184 $ 30,352 $ 32,184 $ 30,352 Less current portion $ (9,117 ) $ (7,151 ) Noncurrent $ 23,067 $ 23,201

FAIR VALUE MEASUREMENTS (Tables

FAIR VALUE MEASUREMENTS (Tables)	9 Months Ended
	Sep. 30, 2018
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following table presents the Company’s liabilities that were measured at fair value on a recurring basis and its categorization within the fair value hierarchy at September 30, 2018 and December 31, 2017 (in thousands): Fair Value September 30, December 31, Warranty obligations Level 3 $ 13,566 $ 9,790 Third party option to purchase receivables at a discount Level 3 — 700
Schedule of Changes in Nonfinancial Liabilities Related to Warrant Obligations Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs	The following table provides information regarding changes in nonfinancial liabilities related to the Company’s warranty obligations measured at fair value on a recurring basis using significant unobservable inputs (Level 3) for the periods indicated (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Balance at beginning of period $ 12,836 $ 12,564 $ 9,790 $ 10,332 Accruals for warranties issued during period 689 867 2,222 2,760 Changes in estimates 853 (1,452 ) 2,848 (2,051 ) Settlements (1,135 ) (530 ) (2,857 ) (1,265 ) Increase due to accretion expense 514 549 1,453 1,542 Other (191 ) (279 ) 110 401 Balance at end of period $ 13,566 $ 11,719 $ 13,566 $ 11,719
Summary of Significant Unobservable Inputs used in the Fair Value Measurement of Liabilities Designated as Level 3	As of September 30, 2018 , 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 16% Credit-adjusted risk-free rate 16% As of December 31, 2017 , the significant unobservable inputs used in the fair value measurement of the Company’s liabilities designated as Level 3 are as follows: Item Measured at Fair Value Valuation Technique Description of Significant Unobservable Input Percent Used (Weighted-Average) Warranty obligations for microinverters sold since January 1, 2014 Discounted cash flows Profit element and risk premium 17% Credit-adjusted risk-free rate 17% Third party option to purchase receivables at a discount Discounted cash flows Counter party credit-adjusted risk-free rate 4%

GOODWILL AND INTANGIBLE ASSETS

GOODWILL AND INTANGIBLE ASSETS (Tables)	9 Months Ended
	Sep. 30, 2018
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill and Intangible Assets	The following table presents the details of the Company’s goodwill and purchased intangible assets as of September 30, 2018 and December 31, 2017 (in thousands): September 30, 2018 December 31, 2017 Gross Additions Accumulated Amortization Net Gross Accumulated Amortization Net Goodwill $ 3,664 $ 21,119 $ — $ 24,783 $ 3,664 $ — $ 3,664 Intangible assets: Other indefinite-lived intangibles $ 286 $ — $ — $ 286 $ 286 $ — $ 286 Intangible assets with finite lives: Patents and licensed technology 1,665 — (1,665 ) — 1,665 (1,436 ) 229 Developed technology — 13,100 (408 ) 12,692 — — — Customer relationships — 23,100 — 23,100 — — — Total purchased intangible assets $ 1,951 $ 36,200 $ (2,073 ) $ 36,078 $ 1,951 $ (1,436 ) $ 515

RESTRUCTURING (Tables)

RESTRUCTURING (Tables)	9 Months Ended
	Sep. 30, 2018
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	The following table presents the details of the Company’s restructuring charges under the 2018 Plan for the periods indicated (in thousands): Three Months Ended Nine Months Ended Redundancy and employee severance and benefit arrangements $ 613 $ 613 Asset impairments 1,636 1,636 Lease loss reserves 339 339 Total restructuring $ 2,588 $ 2,588 The following table presents the details of the Company’s restructuring charges under the 2016 Plan for the periods indicated (in thousands): Three Months Ended Nine Months Ended Employee severance and benefit arrangements $ 1,111 $ 2,826 Asset impairments — 522 Consultants engaged in restructuring activities 3,100 10,100 Lease loss reserves and contract termination costs (140 ) 1,479 Total restructuring $ 4,071 $ 14,927
Schedule of Restructuring Reserve by Type of Cost	The following table provides information regarding changes in the Company’s 2018 Plan accrued restructuring balance for the periods indicated (in thousands): Redundancy and Employee Severance and Benefits Lease Loss Reserves and Contractual Obligations Total Charges $ 613 $ 339 $ 952 Cash payments (297 ) — (297 ) Non-cash settlement and other — 10 10 Balance as of September 30, 2018 $ 316 $ 349 $ 665 The following table provides information regarding changes in the Company’s 2016 Plan accrued restructuring balance for the periods indicated (in thousands): Employee Severance and Benefits Lease Loss Reserves and Contractual Obligations Total Balance as of December 31, 2017 $ 229 $ 1,094 $ 1,323 Cash payments and receipts, net (229 ) 707 478 Non-cash settlement — — — Balance as of September 30, 2018 $ 0 $ 1,801 $ 1,801

DEBT (Tables)

DEBT (Tables)	9 Months Ended
	Sep. 30, 2018
Debt Disclosure [Abstract]
Schedule of Debt	Long-term debt was comprised of the following at September 30, 2018 and December 31, 2017 (in thousands): September 30, December 31, Convertible Notes due 2023 $ 65,000 $ — Less unamortized issuance costs (2,492 ) — Carrying amount of Convertible Notes due 2023 62,508 — Term loan 44,336 50,000 Less unamortized discount and issuance costs (1,299 ) (2,111 ) Carrying amount of term loan 43,037 47,889 Sale of long term financing receivable recorded as debt 6,487 2,562 Less value of future purchase option — (700 ) Carrying amount of sale of long term financing receivable recorded as debt 6,487 1,862 Total carrying amount of debt 112,032 49,751 Less current portion term loan (21,387 ) (15,715 ) Less current portion of long term financing receivable recorded as debt (2,738 ) (1,714 ) Long-term debt $ 87,907 $ 32,322
Schedule of Maturities of Long-term Debt	As of September 30, 2018 , the estimated schedule of principal payments due on the term loan is as follows (in thousands): Year Amounts 2018 (remaining 3 months) $ 2,545 2019 25,497 2020 16,294 Total $ 44,336

STOCK-BASED COMPENSATION (Table

STOCK-BASED COMPENSATION (Tables)	9 Months Ended
	Sep. 30, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Option Activity	The following is a summary of stock option activity for the nine months ended September 30, 2018 (in thousands, except per share data): Number of Weighted- Outstanding at December 31, 2017 8,426 $ 1.77 Granted 213 4.43 Exercised (1,185 ) 1.70 Canceled (292 ) 3.59 Outstanding at September 30, 2018 7,162 1.78 Vested and expected to vest at September 30, 2018 6,727 1.80 Exercisable at September 30, 2018 4,572 1.90
Summary of Restricted Stock Unit Activity	The following is a summary of restricted stock unit (“RSU”) and performance stock unit (“PSU”) activity for the nine months ended September 30, 2018 (in thousands, except per share data): Number of Weighted Average Outstanding at December 31, 2017 3,505 $ 2.03 Granted 4,126 3.67 Vested (1,060 ) 2.63 Canceled (825 ) 1.91 Outstanding at September 30, 2018 5,746 3.11 Expected to vest at September 30, 2018 4,791 3.08
Summary of the Components of Total Stock-Based Compensation Expense	The following table summarizes the components of total stock-based compensation expense included in the condensed consolidated statements of operations for the periods presented (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Cost of revenues $ 330 $ 347 $ 945 $ 796 Research and development 878 607 2,645 1,994 Sales and marketing 1,151 226 2,509 889 General and administrative 1,692 547 3,812 1,598 Total $ 4,051 $ 1,727 $ 9,911 $ 5,277
Summary of Stock-Based Compensation Associated with Each Type of Award	The following table summarizes the various types of stock-based compensation expense for the periods presented (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Stock options and RSUs and PSUs $ 3,708 $ 1,473 $ 9,001 $ 4,363 Employee stock purchase plan 343 254 910 914 Total $ 4,051 $ 1,727 $ 9,911 $ 5,277
Summary of the Weighted-Average Grant Date Fair Value of Options Granted	The following table presents the weighted-average grant date fair value of options granted for the periods presented and the assumptions used to estimate those values using a Black-Scholes option pricing model: Three Months Ended Nine Months Ended 2018 2017 2018 2017 Weighted average grant date fair value ** $ 0.69 $ 2.83 $ 0.70 Expected term (in years) ** 4.2 4.0 4.4 Expected volatility ** 83.8 % 88.5 % 84.4 % Annual risk-free rate of return ** 1.6 % 2.6 % 1.8 % Dividend yield ** 0.0 % 0.0 % 0.0 %

NET LOSS PER SHARE (Tables)

NET LOSS PER SHARE (Tables)	9 Months Ended
	Sep. 30, 2018
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss Per Share	The following table presents the computation of basic and diluted net loss per share for the periods presented (in thousands, except per share data): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Numerator: Net loss $ (3,470 ) $ (6,854 ) $ (12,336 ) $ (42,252 ) Denominator: Weighted average common shares outstanding 102,798 84,862 97,257 81,993 Net loss per share, basic and diluted $ (0.03 ) $ (0.08 ) $ (0.13 ) $ (0.52 )
Schedule of Potentially Dilutive Securities Excluded from the Computation of Diluted Net Loss Per Share	The following outstanding shares of common stock equivalents were excluded from the calculation of the diluted net loss per share attributable to common stockholders because their effect would have been anti-dilutive (in thousands): Three Months Ended Nine Months Ended 2018 2017 2018 2017 Employee stock options 7,404 7,844 7,971 8,121 RSUs and PSUs 5,924 3,306 5,106 1,959 Warrants to purchase common stock — 1,220 — 1,033 Total 13,328 12,370 13,077 11,113 The conversion of the Notes will have a dilutive impact when the average market price of the Company’s common stock for a given period exceeds the conversion price of $5.56 per share. The Notes are convertible at the holder’s option at 180.0180 shares per $1,000 note.

ACQUISITION (Tables)

ACQUISITION (Tables)	9 Months Ended
	Sep. 30, 2018
Business Combinations [Abstract]
Summary of consideration transfered for business acquisition	The acquisition date fair value of the consideration transferred was approximately $57.3 million , which consisted of the following (in thousands): Cash consideration $ 25,000 Common stock issued 32,319 Total $ 57,319 The table below shows estimated fair values of the assets acquired funded by cash and issuance of common stock at the acquisition date (in thousands): Cash Purchase Price Issuance of Common Stock Total Consideration % of Total Consideration Developed technology and goodwill $ 15,000 $ 19,219 $ 34,219 60 % Customer relationship 10,000 13,100 23,100 40 % Total consideration $ 25,000 $ 32,319 $ 57,319 100 %
Summary of fair values of assets acquired and liabilities assumed	The following table summarizes the preliminary estimated fair values of the assets acquired and liabilities assumed at the acquisition date (in thousands): Intangible assets $ 36,200 Goodwill 21,119 Net assets acquired $ 57,319
Summary of identifiable intangible assets acquired	The table below shows estimated fair values of the assets acquired funded by cash and issuance of common stock at the acquisition date (in thousands): Cash Purchase Price Issuance of Common Stock Total Consideration % of Total Consideration Developed technology and goodwill $ 15,000 $ 19,219 $ 34,219 60 % Customer relationship 10,000 13,100 23,100 40 % Total consideration $ 25,000 $ 32,319 $ 57,319 100 % The following table shows the fair value of the separately identifiable intangible assets at the time of acquisition and the period over which each intangible asset will be amortized: Preliminary fair value (in thousands) Useful life (in years) Developed technology $ 13,100 6 Customer relationship 23,100 9 Total identifiable intangible assets $ 36,200

DESCRIPTION OF BUSINESS AND B_3

DESCRIPTION OF BUSINESS AND BASIS OF PRESENTATION (Details) system in Thousands, deliverable in Millions, watt in Billions	Sep. 30, 2018systemcountrydeliverablewatt
Product Information [Line Items]
Number of countries in which product is deployed (country) | country	120
Microinverter
Product Information [Line Items]
Number of product shipped (deliverable) | deliverable	18
Number of watts (watt) | watt	4
Residential and Commercial Systems
Product Information [Line Items]
Number of product deployed (system) | system	820

REVENUE RECOGNITION - Narrative

REVENUE RECOGNITION - Narrative (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)accounting_unit	Jan. 01, 2018USD ($)
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit reduction (increase)	$ (347,011,000)		$ (347,011,000)		$ (295,727,000)	$ 43,400,000
Net increase in revenues	78,002,000	$ 77,038,000	223,870,000	$ 206,492,000
Number of accounting units (accounting unit) | accounting_unit					2
Increase in deferred revenue	106,080,000		106,080,000			116,830,000
Increase in deferred costs						800,000
Accrued liabilities	41,562,000		41,562,000		$ 22,447,000	5,600,000
Contract asset impairment charges	0
Products and services transferred over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net increase in revenues	9,746,000		30,306,000
Products transferred at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net increase in revenues	$ 68,256,000		$ 193,564,000
Envoy Communications Device and Enlighten Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Unbilled revenue						$ 77,500,000
Monitoring Hardware and Service | Incurred Commissions
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Amortization period for capitalized costs						6 years 6 months
Envoy Communications Gateway | Products and services transferred over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognition period	6 years 6 months		6 years 6 months
Communication Accessories | Minimum | Products transferred at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognition period	5 years		5 years
Communication Accessories | Maximum | Products transferred at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognition period	12 years		12 years
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit reduction (increase)	$ (37,630,000)		$ (37,630,000)			$ (38,900,000)
Net increase in revenues	323,000		2,781,000
Accrued liabilities	$ 5,372,000		$ 5,372,000
Adjustments | Accounting Standards Update 2014-09 | Envoy Communications Device and Enlighten Service
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit reduction (increase)						(34,100,000)
Unbilled revenue						6,400,000
Adjustments | Accounting Standards Update 2014-09 | Monitoring Hardware and Service | Incurred Commissions
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Accumulated deficit reduction (increase)						$ 800,000

REVENUE RECOGNITION - Summary o

REVENUE RECOGNITION - Summary of Disaggregated Revenue by Primary Geographical Market and Timing of Revenue Recognition (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 78,002	$ 77,038	$ 223,870	$ 206,492
Products transferred at a point in time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	68,256		193,564
Products and services transferred over time
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	9,746		30,306
United States
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	54,880		148,268
International
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 23,122		$ 75,602

REVENUE RECOGNITION - Summary_2

REVENUE RECOGNITION - Summary of Contract Assets and Contract Liabilities from Contracts with Customers (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Receivables	$ 54,117	$ 65,346
Short-term contract assets (Prepaid expenses and other assets)	12,876
Long-term contract assets (Other assets)	32,967
Short-term contract liabilities (Deferred revenues)	32,015	15,691
Long-term contract liabilities (Deferred revenues)	$ 74,065	$ 29,941

REVENUE RECOGNITION - Summary_3

REVENUE RECOGNITION - Summary of Significant Changes in the Balances of Contract Liabilities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Contract Liabilities
Balance, beginning of period	$ 116,830
Revenue recognized	(36,283)
Increase due to billings	25,533
Balance, end of period	106,080
Short-term contract liabilities (Deferred revenues)	32,015	$ 15,691
Long-term contract liabilities (Deferred revenues)	74,065	$ 29,941
Contract Assets
Balance, beginning of period	47,862
Amount recognized	(11,741)
Increase	9,722
Balance, end of period	$ 45,843

REVENUE RECOGNITION - Summary_4

REVENUE RECOGNITION - Summary of Estimated Revenue Expected to be Recognized in Future Periods (Details) $ in Thousands	Sep. 30, 2018USD ($)
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 106,080
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2018-10-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 8,922
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing	3 months
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2019-01-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 30,505
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2020-01-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 24,352
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-01-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 18,162
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2022-01-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 13,112
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing	1 year
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-01-01
Revenue from Contract with Customer [Abstract]
Total estimated revenue expected to be recognized in future periods	$ 11,027
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Total estimated revenue expected to be recognized in future periods, expected timing

REVENUE RECOGNITION - Summary_5

REVENUE RECOGNITION - Summary of New Accounting Adoption Impact on Consolidated Statements of Income (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 78,002	$ 77,038	$ 223,870	$ 206,492
Cost of revenues	52,738	60,577	157,589	169,438
Gross profit	25,264	16,461	66,281	37,054
Operating expenses:
Research and development	8,165	7,397	25,247	24,949
Sales and marketing	7,375	5,453	20,430	18,186
General and administrative	7,510	5,441	21,423	16,238
Restructuring charges	2,588	4,071	2,588	14,927
Total operating expenses	25,638	22,362	69,688	74,300
Loss from operations	(374)	(5,901)	(3,407)	(37,246)
Other expense, net
Interest expense	(2,469)	(1,760)	(7,031)	(5,979)
Other expense	(379)	623	(1,077)	1,771
Total other expense, net	(2,848)	(1,137)	(8,108)	(4,208)
Loss before income taxes	(3,222)	(7,038)	(11,515)	(41,454)
Income tax provision	(248)	184	(821)	(798)
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)	$ (0.08)	$ (0.13)	$ (0.52)
Shares used in per share calculation:
Basic and diluted (in shares)	102,798	84,862	97,257	81,993
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 323		$ 2,781
Cost of revenues	413		1,409
Gross profit	(90)		1,372
Operating expenses:
Research and development	0		0
Sales and marketing	0		58
General and administrative	0		0
Restructuring charges	0		0
Total operating expenses	0		58
Loss from operations	(90)		1,314
Other expense, net
Interest expense	0		0
Other expense	0		0
Total other expense, net	0		0
Loss before income taxes	(90)		1,314
Income tax provision	0		0
Net loss	$ (90)		$ 1,314
Net loss per share:
Basic and diluted (in usd per share)	$ 0		$ 0.01
Without Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net revenues	$ 77,679		$ 221,089
Cost of revenues	52,325		156,180
Gross profit	25,354		64,909
Operating expenses:
Research and development	8,165		25,247
Sales and marketing	7,375		20,372
General and administrative	7,510		21,423
Restructuring charges	2,588		2,588
Total operating expenses	25,638		69,630
Loss from operations	(284)		(4,721)
Other expense, net
Interest expense	(2,469)		(7,031)
Other expense	(379)		(1,077)
Total other expense, net	(2,848)		(8,108)
Loss before income taxes	(3,132)		(12,829)
Income tax provision	(248)		(821)
Net loss	$ (3,380)		$ (13,650)
Net loss per share:
Basic and diluted (in usd per share)	$ (0.03)		$ (0.14)
Shares used in per share calculation:
Basic and diluted (in shares)	102,798		97,257

REVENUE RECOGNITION - Summary_6

REVENUE RECOGNITION - Summary of New Accounting Adoption Impact on Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other assets	$ 21,631		$ 9,957
Other assets	35,520		8,039
Accrued liabilities	41,562	$ 5,600	22,447
Deferred revenues, current	32,015		15,691
Deferred revenues, noncurrent	74,065		29,941
Accumulated deficit	(347,011)	43,400	$ (295,727)
Adjustments | Accounting Standards Update 2014-09
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other assets	9,465
Other assets	28,450
Accrued liabilities	5,372
Deferred revenues, current	19,369
Deferred revenues, noncurrent	50,804
Accumulated deficit	(37,630)	$ (38,900)
Without Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Prepaid expenses and other assets	12,166
Other assets	7,070
Accrued liabilities	36,190
Deferred revenues, current	12,646
Deferred revenues, noncurrent	23,261
Accumulated deficit	$ (309,381)

INVENTORY - Summary of Inventor

INVENTORY - Summary of Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Schedule of inventory
Raw materials	$ 1,467	$ 2,341
Finished goods	16,419	23,658
Total inventory	$ 17,886	$ 25,999

WARRANTY OBLIGATIONS - Summary

WARRANTY OBLIGATIONS - Summary of Warranty Activities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Changes in the Company's product warranty liability
Warranty obligations, beginning of period	$ 31,642	$ 31,613	$ 29,816	$ 31,414
Accruals for warranties issued during period	689	1,009	2,222	2,913
Changes in estimates	1,997	(1,046)	4,825	(826)
Settlements	(2,467)	(1,494)	(6,242)	(5,092)
Increase due to accretion expense	514	549	1,453	1,542
Other	(191)	(279)	110	401
Warranty obligations, end of period	32,184	30,352	32,184	30,352
Less current portion	(9,117)	(7,151)	(9,117)	(7,151)	$ (7,427)
Noncurrent	$ 23,067	$ 23,201	$ 23,067	$ 23,201	$ 22,389

WARRANTY OBLIGATIONS - Narrativ

WARRANTY OBLIGATIONS - Narrative (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Product Warranties Disclosures [Abstract]
Warranty obligations	$ 32,184	$ 31,642	$ 29,816	$ 30,352	$ 31,613	$ 31,414
Fair value liabilities	$ 13,600

FAIR VALUE MEASUREMENTS - Sched

FAIR VALUE MEASUREMENTS - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016
Liabilities:
Fair value liabilities	$ 13,600
Recurring | Level 3 | Warranty obligations
Liabilities:
Fair value liabilities	13,566	$ 12,836	$ 9,790	$ 11,719	$ 12,564	$ 10,332
Recurring | Level 3 | Third party option to purchase receivables at a discount
Liabilities:
Fair value liabilities	$ 0		$ 700

FAIR VALUE MEASUREMENTS - Sch_2

FAIR VALUE MEASUREMENTS - Schedule of Changes in Nonfinancial Liabilities Related to Warrant Obligations Measured at Fair Value on a Recurring Basis Using Significant Unobservable Inputs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at end of period	$ 13,600		$ 13,600
Level 3 | Recurring | Warranty obligations
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	12,836	$ 12,564	9,790	$ 10,332
Accruals for warranties issued during period	689	867	2,222	2,760
Changes in estimates	853	(1,452)	2,848	(2,051)
Settlements	(1,135)	(530)	(2,857)	(1,265)
Increase due to accretion expense	514	549	1,453	1,542
Other	(191)	(279)	110	401
Balance at end of period	$ 13,566	$ 11,719	$ 13,566	$ 11,719

FAIR VALUE MEASUREMENTS - Summa

FAIR VALUE MEASUREMENTS - Summary of Significant Unobservable Inputs used in the Fair Value Measurement of Liabilities Designated as Level 3 (Details) - Recurring - Level 3	Sep. 30, 2018	Dec. 31, 2017
Measurement Input, Profit Element and Risk Premium | Warranty obligations for microinverters sold since January 1, 2014
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warranty obligations for microinverters sold since January 1, 2014	0.16	0.17
Measurement Input, Entity Credit Risk | Warranty obligations for microinverters sold since January 1, 2014
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Warranty obligations for microinverters sold since January 1, 2014	0.16	0.17
Measurement Input, Counterparty Credit Risk | Third party option to purchase receivables at a discount
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Third party option to purchase receivables at a discount		0.04

FAIR VALUE MEASUREMENTS - Narra

FAIR VALUE MEASUREMENTS - Narrative (Details) $ in Millions	9 Months Ended
	Sep. 30, 2018USD ($)
Fair Value Disclosures [Abstract]
Increase in liability as a result of decreasing the profit element and risk premium input by 100 basis points	$ 0.1
Decrease in liability as a result of increasing the profit element and risk premium input by 100 basis points	0.1
Increase to fair value measurement as a result of 100 basis point decrease	0.6
Decrease to fair value measurement as a result of 100 basis point increase	$ 0.6

GOODWILL AND INTANGIBLE ASSET_2

GOODWILL AND INTANGIBLE ASSETS - Schedule of Goodwill and Intangible Assets (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2018	Dec. 31, 2017
Finite-Lived Intangible Assets [Line Items]
Goodwill, Gross	$ 3,664	$ 3,664
Goodwill, Additions	21,119
Goodwill, Net	24,783	3,664
Intangible Assets, Net (Excluding Goodwill) [Abstract]
Other indefinite-lived intangibles, Gross	286	286
Other indefinite-lived intangibles, Acquired	0
Intangible assets with finite lives:
Gross	1,951	1,951
Additions	36,200
Accumulated Amortization	(2,073)	(1,436)
Net	36,078	515
Patents and licensed technology
Intangible assets with finite lives:
Gross	1,665	1,665
Additions	0
Accumulated Amortization	(1,665)	(1,436)
Net	0	229
Developed technology
Intangible assets with finite lives:
Gross	0	0
Additions	13,100
Accumulated Amortization	(408)	0
Net	12,692	0
Customer relationship
Intangible assets with finite lives:
Gross	0	0
Additions	23,100
Accumulated Amortization	0	0
Net	$ 23,100	$ 0

GOODWILL AND INTANGIBLE ASSET_3

GOODWILL AND INTANGIBLE ASSETS - Narrative (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		9 Months Ended
	Oct. 31, 2015	Jul. 31, 2014	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Finite-Lived Intangible Assets [Line Items]
Amortization expense related to intangible assets			$ 0.5	$ 0.1	$ 0.6	$ 0.4
Patents
Finite-Lived Intangible Assets [Line Items]
Useful life		3 years
ASIC development
Finite-Lived Intangible Assets [Line Items]
Useful life	3 years

RESTRUCTURING - Summary of Rest

RESTRUCTURING - Summary of Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Restructuring Plan 2018
Restructuring Cost and Reserve [Line Items]
Total restructuring	$ 2,588		$ 2,588
Restructuring Plan 2018 | Redundancy and Employee Severance and Benefits
Restructuring Cost and Reserve [Line Items]
Total restructuring	613		613
Restructuring Plan 2018 | Asset impairments
Restructuring Cost and Reserve [Line Items]
Total restructuring	1,636		1,636
Restructuring Plan 2018 | Lease loss reserves and contract termination costs
Restructuring Cost and Reserve [Line Items]
Total restructuring	$ 339		$ 339
Restructuring Plan 2016
Restructuring Cost and Reserve [Line Items]
Total restructuring		$ 4,071		$ 14,927
Restructuring Plan 2016 | Redundancy and Employee Severance and Benefits
Restructuring Cost and Reserve [Line Items]
Total restructuring		1,111		2,826
Restructuring Plan 2016 | Asset impairments
Restructuring Cost and Reserve [Line Items]
Total restructuring		0		522
Restructuring Plan 2016 | Consultants engaged in restructuring activities
Restructuring Cost and Reserve [Line Items]
Total restructuring		3,100		10,100
Restructuring Plan 2016 | Lease loss reserves and contract termination costs
Restructuring Cost and Reserve [Line Items]
Total restructuring		$ (140)		$ 1,479

RESTRUCTURING - Rollforward (De

RESTRUCTURING - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2018
Restructuring Plan 2018
Restructuring Reserve [Roll Forward]
Charges	$ 952
Cash payments	(297)
Non-cash settlement and other	10
Ending balance	665	$ 665
Restructuring Plan 2018 | Employee Severance and Benefits
Restructuring Reserve [Roll Forward]
Charges	613
Cash payments	(297)
Non-cash settlement and other	0
Ending balance	316	316
Restructuring Plan 2018 | Lease Loss Reserves and Contractual Obligations
Restructuring Reserve [Roll Forward]
Charges	339
Cash payments	0
Non-cash settlement and other	10
Ending balance	349	349
Restructuring Plan 2016
Restructuring Reserve [Roll Forward]
Beginning balance		1,323
Cash payments		478
Non-cash settlement and other		0
Ending balance	1,801	1,801
Restructuring Plan 2016 | Employee Severance and Benefits
Restructuring Reserve [Roll Forward]
Beginning balance		229
Cash payments		(229)
Non-cash settlement and other		0
Ending balance	0	0
Restructuring Plan 2016 | Lease Loss Reserves and Contractual Obligations
Restructuring Reserve [Roll Forward]
Beginning balance		1,094
Cash payments		707
Non-cash settlement and other		0
Ending balance	$ 1,801	$ 1,801

DEBT - Long term debt (Details)

DEBT - Long term debt (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Total carrying amount of debt	$ 112,032	$ 49,751
Debt, current	(24,125)	(17,429)
Debt, noncurrent	87,907	32,322
Convertible Notes Payable | Convertible Senior Notes Due 2023
Debt Instrument [Line Items]
Carrying amount of long term debt	65,000	0
Less unamortized discount and issuance costs	(2,492)	0
Total carrying amount of debt	62,508	0
Secured Debt | Term Loan Agreement, July 2016
Debt Instrument [Line Items]
Carrying amount of long term debt	44,336	50,000
Less unamortized discount and issuance costs	(1,299)	(2,111)
Total carrying amount of debt	43,037	47,889
Debt, current	(21,387)	(15,715)
Financing Receivable | Financing Receivable Recorded as Debt
Debt Instrument [Line Items]
Carrying amount of long term debt	6,487	2,562
Less value of future purchase option	0	(700)
Total carrying amount of debt	6,487	1,862
Debt, current	$ (2,738)	$ (1,714)

DEBT - Narrative (Details)

DEBT - Narrative (Details)	Feb. 28, 2018USD ($)$ / sharesshares	Aug. 31, 2018USD ($)$ / shares	Feb. 28, 2018USD ($)$ / sharesshares	Dec. 31, 2017USD ($)	Feb. 28, 2017USD ($)	Jul. 31, 2016USD ($)	Sep. 30, 2018USD ($)shares	Sep. 30, 2017USD ($)	Dec. 31, 2016USD ($)	Nov. 30, 2012USD ($)
Short-term Debt [Line Items]
Proceeds from debt							$ 68,352,000	$ 24,240,000
Payments under revolving credit facility							0	10,100,000
Fair value of warrants issued	$ 1,400,000		$ 1,400,000				0	$ 1,447,000
Value of future purchase option				$ 700,000
Measurement Input, Quoted Price | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights, measurement input | $ / shares	1.05		1.05
Measurement Input, Share Price | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights, measurement input | $ / shares	1.56		1.56
Measurement Input, Price Volatility | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights, measurement input	0.859		0.859
Measurement Input, Risk Free Interest Rate | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights, measurement input	0.0223		0.0223
Measurement Input, Expected Dividend Rate | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights, measurement input	0		0
Measurement Input, Expected Term | Cashless Exercise Warrants
Short-term Debt [Line Items]
Warrants and rights outstanding, term	7 years		7 years
Tennenbaum Capital Partners, LLC | Secured Debt
Short-term Debt [Line Items]
Debt instrument face amount						$ 25,000,000
Proceeds from debt						$ 25,000,000
Interest rate during period						10.25%
Commitment fee percentage						3.30%
Closing fee						10.00%
Tennenbaum Capital Partners, LLC | Secured Debt | Minimum
Short-term Debt [Line Items]
Prepayment fee						1.00%
Tennenbaum Capital Partners, LLC | Secured Debt | Maximum
Short-term Debt [Line Items]
Prepayment fee						3.00%
Tennenbaum Capital Partners, LLC | Secured Debt | LIBOR
Short-term Debt [Line Items]
Interest rate during period						9.5625%
Reduction of interest rate during period						1.00%
Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC | Secured Debt
Short-term Debt [Line Items]
Debt instrument face amount					$ 25,000,000
Second Amendment To Term Loans | Secured Debt
Short-term Debt [Line Items]
Percent decrease in principal payments	50.00%
Convertible Notes Payable | Convertible Senior Notes Due 2023
Short-term Debt [Line Items]
Debt instrument face amount		$ 60,000,000
Proceeds from issuance of debt		62,400,000
Debt underwriter fees		2,000,000
Debt issuance costs		$ 600,000
Interest rate		4.00%
Principal amount multiples		$ 1,000
Conversion rate of common stock (in dollars per share)		0.1800180
Debt conversion price (in usd per share) | $ / shares		$ 5.56
Redemption price percentage		100.00%
Unamortized issuance costs and debt discounts				0			$ 2,492,000
Secured Debt | Amended Term Loan Agreement, February 2017 | Closing Date to March 31, 2018
Short-term Debt [Line Items]
Liquidity ratio required			1.5
Secured Debt | Amended Term Loan Agreement, February 2017 | April 1, 2018 and Thereafter
Short-term Debt [Line Items]
Liquidity ratio required			1.75
Secured Debt | Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC
Short-term Debt [Line Items]
Interest rate during period					10.3125%
Commitment fee percentage					3.00%
Closing fee					4.00%
Unrestricted cash			$ 10,000,000
Number of securities called by warrants (in shares) | shares	1,220,000		1,220,000				912,067
Class of warrant term year			7 years
Secured Debt | Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC | Measurement Input, Quoted Price
Short-term Debt [Line Items]
Warrants and rights, measurement input | $ / shares	1.05		1.05
Secured Debt | Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC | Minimum
Short-term Debt [Line Items]
Prepayment fee					1.00%
Secured Debt | Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC | Maximum
Short-term Debt [Line Items]
Prepayment fee					3.00%
Secured Debt | Amended Term Loan Agreement, February 2017 | Tennenbaum Capital Partners, LLC | LIBOR
Short-term Debt [Line Items]
Basis spread on variable rate					9.25%
Secured Debt | Term Loan Agreement, July 2016
Short-term Debt [Line Items]
Unamortized issuance costs and debt discounts				2,111,000			$ 1,299,000
Secured Debt | Term Loan Agreement, July 2016 | Tennenbaum Capital Partners, LLC
Short-term Debt [Line Items]
Debt instrument face amount						$ 25,000,000
Line of Credit | Wells Fargo Bank | Revolving Credit Facility
Short-term Debt [Line Items]
Payments under revolving credit facility						$ 10,300,000
Maximum borrowing capacity										$ 50,000,000
Revolving credit facility									$ 10,100,000
Financing Receivable | Financing Receivable Recorded as Debt
Short-term Debt [Line Items]
Proceeds from debt				$ 2,800,000			$ 5,600,000
Thurman John Rodgers | Convertible Notes Payable | Convertible Senior Notes Due 2023
Short-term Debt [Line Items]
Debt instrument face amount		$ 5,000,000

DEBT - Maturities (Details)

DEBT - Maturities (Details) - Secured Debt - Second Amendment To Term Loans $ in Thousands	Sep. 30, 2018USD ($)
Debt Instrument [Line Items]
2018 (remaining 3 months)	$ 2,545
2,019	25,497
2,020	16,294
Total	$ 44,336

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) - USD ($) $ in Thousands	Dec. 28, 2018	Dec. 10, 2018	Aug. 09, 2018	Jun. 30, 2018	Sep. 30, 2018	Sep. 30, 2017	Apr. 12, 2018	Mar. 31, 2018
Loss Contingencies [Line Items]
Accrual for legal settlements								$ 1,800
Accrual for legal settlements				$ 1,800
Lease term							5 years
Lease renewal option							5 years
Remaining facility lease obligation					$ 2,200
Cash paid for business acquisition					$ 9,000	$ 0
SunPower’s
Loss Contingencies [Line Items]
Cash consideration			$ 15,000
Cash paid for business acquisition			$ 15,000
SunPower’s | Forecast
Loss Contingencies [Line Items]
Cash consideration		$ 10,000
Additional cash consideration, period	4 months

SALE OF COMMON STOCK (Details)

SALE OF COMMON STOCK (Details) - USD ($) $ / shares in Units, $ in Thousands	Feb. 04, 2018	Sep. 30, 2018	Sep. 30, 2017
Subsidiary, Sale of Stock [Line Items]
Proceeds from issuance of common stock		$ 19,771	$ 26,425
Private Placement
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	9,523,809
Price per share issued (in usd per share)	$ 2.10
Proceeds from issuance of common stock	$ 20,000

STOCK-BASED COMPENSATION - Narr

STOCK-BASED COMPENSATION - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 03, 2017	Sep. 30, 2018	Jun. 30, 2018	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Intrinsic value of options exercised				$ 4.6
Intrinsic value of options outstanding		$ 23.4		23.4
Fair value of stock vested during period				4.8
Intrinsic value of restricted stock units outstanding		$ 27.9		$ 27.9
Award granted (in shares)		0
Common stock to be purchased in exchange for options (in shares)	2,362,470			292,000
Total unrecognized compensation cost		$ 16.3		$ 16.3
Weighted-average recognition period for unrecognized compensation cost				2 years 5 months
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance target percentage			0.00%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance target percentage			150.00%
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award granted (in shares)			1,400,000
Weighted average estimated fair value of award (in usd per share)			$ 4.57
Performance Shares with Market Conditions
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award granted (in shares)			720,000
Weighted average estimated fair value of award (in usd per share)			$ 4.54
Restricted stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock to be purchased in exchange for options (in shares)	733,559

STOCK-BASED COMPENSATION - Summ

STOCK-BASED COMPENSATION - Summary of Stock Option Activity (Details) - $ / shares	Apr. 03, 2017	Sep. 30, 2018
Number of Shares Outstanding
Outstanding, beginning balance (in shares)		8,426,000
Granted (in shares)		213,000
Exercised (in shares)		(1,185,000)
Canceled (in shares)	(2,362,470)	(292,000)
Outstanding, ending balance (in shares)		7,162,000
Vested and expected to vest (in shares)		6,727,000
Exercisable (in shares)		4,572,000
Weighted- Average Exercise Price per Share
Outstanding, beginning balance (in usd per share)		$ 1.77
Granted (in usd per share)		4.43
Exercised (in usd per share)		1.70
Canceled (in usd per share)		3.59
Outstanding, ending balance (in usd per share)		1.78
Vested and expected (in usd per share)		1.80
Exercisable (in usd per share)		$ 1.90

STOCK-BASED COMPENSATION - Su_2

STOCK-BASED COMPENSATION - Summary of Restricted Stock Unit Activity (Details)	3 Months Ended	9 Months Ended
	Sep. 30, 2018$ / sharesshares	Sep. 30, 2018$ / sharesshares
Number of Shares Outstanding
Granted (in shares)	0
Restricted stock units
Number of Shares Outstanding
Outstanding, beginning balance (in shares)		3,505,000
Granted (in shares)		4,126,000
Vested (in shares)		(1,060,000)
Canceled (in shares)		(825,000)
Outstanding, ending balance (in shares)	5,746,000	5,746,000
Expected to vest (in shares)	4,791,000	4,791,000
Weighted Average Fair Value per Share at Grant Date
Outstanding, beginning balance (in usd per share) | $ / shares		$ 2.03
Granted (in usd per share) | $ / shares		3.67
Vested (in usd per share) | $ / shares		2.63
Canceled (in usd per share) | $ / shares		1.91
Outstanding, ending balance (in usd per share) | $ / shares	$ 3.11	3.11
Expected to vest (in usd per share) | $ / shares	$ 3.08	$ 3.08

STOCK-BASED COMPENSATION - Su_3

STOCK-BASED COMPENSATION - Summary of the Components of Total Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Allocation of Stock-based Compensation Expense Included in the Consolidated Statement of Operations [Abstract]
Total stock-based compensation expense	$ 4,051	$ 1,727	$ 9,911	$ 5,277
Cost of revenues
Allocation of Stock-based Compensation Expense Included in the Consolidated Statement of Operations [Abstract]
Total stock-based compensation expense	330	347	945	796
Research and development
Allocation of Stock-based Compensation Expense Included in the Consolidated Statement of Operations [Abstract]
Total stock-based compensation expense	878	607	2,645	1,994
Sales and marketing
Allocation of Stock-based Compensation Expense Included in the Consolidated Statement of Operations [Abstract]
Total stock-based compensation expense	1,151	226	2,509	889
General and administrative
Allocation of Stock-based Compensation Expense Included in the Consolidated Statement of Operations [Abstract]
Total stock-based compensation expense	$ 1,692	$ 547	$ 3,812	$ 1,598

STOCK-BASED COMPENSATION - Su_4

STOCK-BASED COMPENSATION - Summary of Stock-Based Compensation Associated with Each Type of Award (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 4,051	$ 1,727	$ 9,911	$ 5,277
Stock options and RSUs and PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	3,708	1,473	9,001	4,363
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation expense	$ 343	$ 254	$ 910	$ 914

STOCK-BASED COMPENSATION - Su_5

STOCK-BASED COMPENSATION - Summary of the Weighted-Average Grant Date Fair Value of Options Granted (Details) - Stock options - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
The fair value of each option granted during the periods
Weighted average grant date fair value (in usd per share)	$ 0.69	$ 2.83	$ 0.70
Expected term (in years)	4 years 2 months	4 years	4 years 5 months
Expected volatility	83.80%	88.50%	84.40%
Annual risk-free rate of return	1.60%	2.60%	1.80%
Dividend yield	0.00%	0.00%	0.00%

NET LOSS PER SHARE - Schedule o

NET LOSS PER SHARE - Schedule of Computation of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Numerator:
Net loss	$ (3,470)	$ (6,854)	$ (12,336)	$ (42,252)
Denominator:
Weighted average common shares outstanding (in shares)	102,798	84,862	97,257	81,993
Net loss per share, basic and diluted (in usd per share)	$ (0.03)	$ (0.08)	$ (0.13)	$ (0.52)

NET LOSS PER SHARE - Schedule_2

NET LOSS PER SHARE - Schedule of Potentially Dilutive Securities Excluded from the Computation of Diluted Net Loss Per Share (Details) shares in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Aug. 31, 2018$ / shares	Sep. 30, 2018shares	Sep. 30, 2017shares	Sep. 30, 2018shares	Sep. 30, 2017shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)		13,328	12,370	13,077	11,113
Convertible Notes Payable | Convertible Senior Notes Due 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Debt conversion price (in usd per share) | $ / shares	$ 5.56
Conversion rate of common stock (in dollars per share)	0.1800180
Employee stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)		7,404	7,844	7,971	8,121
RSUs and PSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)		5,924	3,306	5,106	1,959
Warrants to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Total (in shares)		0	1,220	0	1,033

ACQUISITION - Narrative (Detail

ACQUISITION - Narrative (Details) $ in Thousands	Dec. 10, 2018USD ($)	Aug. 09, 2018USD ($)shares	Sep. 30, 2018USD ($)	Sep. 30, 2017USD ($)	Dec. 31, 2017USD ($)
Business Acquisition [Line Items]
Goodwill			$ 24,783		$ 3,664
Cash purchase price allocated in cash flows from operating activities			(11,384)	$ (3,609)
Acquisition funded by issuance of common stock			19,219	0
Acquisition funded by accrued liabilities			6,000	0
Cash purchase price allocated in cash flows from investing activities			14,257	$ (26,528)
SunPower’s
Business Acquisition [Line Items]
Agreement for exclusive supplier rights, period		5 years
Consideration transfered for business acquisition		$ 57,319
Cash consideration		$ 15,000
Common stock issued for business acquisition (in shares) | shares		7,500,000
Issuance of Common Stock		$ 32,319
Limitation for trade or transfer, period		6 months
Limitation for number of shares to be transfered by acquiree, period		6 months
Goodwill		$ 21,119
Cash purchase price allocated in cash flows from operating activities		9,000
Acquisition funded by issuance of common stock			19,200
Acquisition funded by accrued liabilities			6,000
Cash purchase price allocated in cash flows from investing activities		$ 6,000
Total acquisition related costs			$ 800
SunPower’s | Developed technology
Business Acquisition [Line Items]
Amortization period for acquired intangible assets		6 years
SunPower’s | Customer relationship
Business Acquisition [Line Items]
Consideration transfered for business acquisition		$ 23,100
Issuance of Common Stock		$ 13,100
Amortization period for acquired intangible assets		9 years
SunPower’s | Forecast
Business Acquisition [Line Items]
Cash consideration	$ 10,000
Measurement Input, Discount Rate | SunPower’s | Minimum
Business Acquisition [Line Items]
Equity, measurement input		0.14
Measurement Input, Discount Rate | SunPower’s | Maximum
Business Acquisition [Line Items]
Equity, measurement input		0.3

ACQUISITION - Summary of Consid

ACQUISITION - Summary of Consideration Transfered for Business Acquisition (Details) - SunPower’s $ in Thousands	Aug. 09, 2018USD ($)
Business Acquisition [Line Items]
Cash Purchase Price	$ 25,000
Cash consideration	15,000
Common stock issued	32,319
Total	$ 57,319

ACQUISITION - Summary of Fair V

ACQUISITION - Summary of Fair Values of Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Aug. 09, 2018	Dec. 31, 2017
Business Acquisition [Line Items]
Goodwill	$ 24,783		$ 3,664
SunPower’s
Business Acquisition [Line Items]
Intangible assets		$ 36,200
Goodwill		21,119
Net assets acquired		$ 57,319

ACQUISITION - Summary of Identi

ACQUISITION - Summary of Identifiable Intangible Assets Acquired (Details) - SunPower’s $ in Thousands	Aug. 09, 2018USD ($)
Business Acquisition [Line Items]
Intangible assets	$ 36,200
Developed technology
Business Acquisition [Line Items]
Intangible assets	$ 13,100
Useful life (in years)	6 years
Customer relationship
Business Acquisition [Line Items]
Intangible assets	$ 23,100
Useful life (in years)	9 years

ACQUISITION - Summary of Alloca

ACQUISITION - Summary of Allocation of Purchase Price to Intangible Assets and Goodwill (Details) - SunPower’s $ in Thousands	Aug. 09, 2018USD ($)
Business Acquisition [Line Items]
Cash Purchase Price	$ 25,000
Issuance of Common Stock	32,319
Total	$ 57,319
Concentration Risk, Percentage	100.00%
Developed technology and goodwill
Business Acquisition [Line Items]
Cash Purchase Price	$ 15,000
Issuance of Common Stock	19,219
Total	$ 34,219
Concentration Risk, Percentage	60.00%
Customer relationship
Business Acquisition [Line Items]
Cash Purchase Price	$ 10,000
Issuance of Common Stock	13,100
Total	$ 23,100
Concentration Risk, Percentage	40.00%