Acacia Communications (ACIA) 10-Q 3 May 18 2018 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	Apr. 27, 2018
Document And Entity Information [Abstract]
Entity Registrant Name	Acacia Communications, Inc.
Trading Symbol	ACIA
Entity Central Index Key	1,651,235
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2,018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		40,149,541

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Current assets:
Cash and cash equivalents	$ 85,135	$ 67,495
Marketable securities - short-term	222,540	211,933
Accounts receivable	74,765	86,602
Inventory	57,156	62,232
Prepaid expenses and other current assets	19,481	18,985
Total current assets	459,077	447,247
Marketable securities - long-term	59,831	85,182
Property and equipment, net	30,426	28,175
Deferred tax asset	45,089	41,901
Other assets	8,517	8,745
Total assets	602,940	611,250
Current liabilities:
Accounts payable	34,527	47,819
Accrued liabilities	42,782	37,234
Deferred revenue	1,360	573
Total current liabilities	78,669	85,626
Income taxes payable	19,205	21,034
Other long-term liabilities	4,857	2,540
Total liabilities	102,731	109,200
Commitments and contingencies (Note 11)
Stockholders’ equity:
Preferred stock, $0.0001 par value; 5,000 shares authorized; none issued and outstanding at March 31, 2018 and December 31, 2017	0	0
Common stock, $0.0001 par value; 150,000 shares authorized; 40,061 and 39,606 shares issued and outstanding at March 31, 2018 and December 31, 2017, respectively	4	4
Additional paid-in capital	332,426	324,944
Accumulated other comprehensive loss	(722)	(320)
Retained earnings	168,501	177,422
Total stockholders’ equity	500,209	502,050
Total liabilities and stockholders’ equity	$ 602,940	$ 611,250

CONDENSED CONSOLIDATED BALANCE3

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares	Mar. 31, 2018	Dec. 31, 2017
Statement of Financial Position [Abstract]
Preferred stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	5,000,000	5,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in USD per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	150,000,000	150,000,000
Common stock, shares issued (in shares)	40,061,000	39,606,000
Common stock, shares outstanding (in shares)	40,061,000	39,606,000

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Income Statement [Abstract]
Revenue	$ 72,941	$ 114,667
Cost of revenue	48,870	58,367
Gross profit	24,071	56,300
Operating expenses:
Research and development	24,445	17,728
Sales, general and administrative	14,288	8,691
Total operating expenses	38,733	26,419
(Loss) income from operations	(14,662)	29,881
Other income, net:
Interest income, net	1,354	445
Other expense, net	(71)	(38)
Total other income, net	1,283	407
(Loss) income before benefit from income taxes	(13,379)	30,288
Benefit from income taxes	(4,301)	(5,421)
Net (loss) income	$ (9,078)	$ 35,709
(Loss) earnings per share:
Basic (in USD per share)	$ (0.23)	$ 0.93
Diluted (in USD per share)	$ (0.23)	$ 0.86
Weighted-average shares used to compute (loss) earnings per share:
Basic (in shares)	39,836	38,308
Diluted (in shares)	39,836	41,654

CONDENSED CONSOLIDATED STATEME5

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE (LOSS) INCOME - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Net (loss) income	$ (9,078)	$ 35,709
Other comprehensive loss:
Changes in unrealized loss on marketable securities, net of income taxes of $88 and $15 for the three months ended March 31, 2018 and 2017, respectively	(402)	(36)
Comprehensive (loss) income	$ (9,480)	$ 35,673

CONDENSED CONSOLIDATED STATEME6

CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement of Comprehensive Income [Abstract]
Changes in unrealized loss on marketable securities, tax	$ 88	$ 15

CONDENSED CONSOLIDATED STATEME7

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Loss	Retained Earnings
Beginning balance (in shares) at Dec. 31, 2016		37,998
Beginning balance at Dec. 31, 2016	$ 434,795	$ 4	$ 295,893	$ (16)	$ 138,914
Vesting of restricted common stock (in shares)		28
Exercise of common stock options (in shares)		341
Exercise of common stock options	883		883
Vesting of restricted stock units (in shares)		149
Stock-based compensation expense	4,632		4,632
Unrealized losses on marketable securities, net of tax	(36)			(36)
Net (loss) income	35,709				35,709
Ending balance (in shares) at Mar. 31, 2017		38,516
Ending balance at Mar. 31, 2017	475,983	$ 4	301,408	(52)	174,623
Adoption of ASU 2014-09, net of tax of $51 (see Note 2)	157				157
Beginning balance (in shares) at Dec. 31, 2017		39,606
Beginning balance at Dec. 31, 2017	$ 502,050	$ 4	324,944	(320)	177,422
Vesting of restricted common stock (in shares)		21
Exercise of common stock options (in shares)	220	220
Exercise of common stock options	$ 968		968
Vesting of restricted stock units (in shares)		214
Stock-based compensation expense	6,514		6,514
Unrealized losses on marketable securities, net of tax	(402)			(402)
Net (loss) income	(9,078)				(9,078)
Ending balance (in shares) at Mar. 31, 2018		40,061
Ending balance at Mar. 31, 2018	$ 500,209	$ 4	$ 332,426	$ (722)	$ 168,501

CONDENSED CONSOLIDATED STATEME8

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Statement of Stockholders' Equity [Abstract]
Changes in unrealized loss on marketable securities, tax	$ 88
Adoption of ASU 2014-09, tax	$ 51

CONDENSED CONSOLIDATED STATEME9

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
CASH FLOWS FROM OPERATING ACTIVITIES:
Net (loss) income	$ (9,078)	$ 35,709
Adjustments to reconcile net (loss) income to net cash provided by operating activities:
Depreciation	3,266	2,877
Stock-based compensation	6,538	4,632
Deferred income taxes	(3,239)	(1,490)
Other non-cash charges	45	76
Changes in operating assets and liabilities:
Accounts receivable	11,837	(6,764)
Inventory	5,076	(2,003)
Prepaid expenses and other current assets	(665)	(5,435)
Other assets	208	(3,566)
Accounts payable	(12,105)	(11,533)
Accrued liabilities	5,527	1,790
Deferred revenue	3,358	211
Income taxes payable	(1,829)	0
Other long-term liabilities	121	356
Net cash provided by operating activities	9,060	14,860
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of property and equipment	(6,704)	(5,608)
Purchases of marketable securities	(73,534)	(116,652)
Sales and maturities of marketable securities	87,830	38,900
Deposits	20	0
Net cash provided by (used in) investing activities	7,612	(83,360)
CASH FLOWS FROM FINANCING ACTIVITIES:
Payment of public offering costs	0	(188)
Proceeds from the issuance of common stock under stock-based compensation plans	968	883
Net cash provided by financing activities	968	695
Net increase (decrease) in cash, cash equivalents and restricted cash	17,640	(67,805)
Cash, cash equivalents and restricted cash—Beginning of period	67,495	208,032
Cash, cash equivalents and restricted cash—End of period	85,135	140,227
Supplemental cash flow disclosures:
Refunds received for income taxes, net	(72)	(134)
Supplemental disclosure of non-cash investing and financing activities:
Capital expenditures incurred but not yet paid	1,555	1,147
Public offering costs incurred but not yet paid	$ 0	$ 13

NATURE OF THE BUSINESS AND OPER

NATURE OF THE BUSINESS AND OPERATIONS	3 Months Ended
	Mar. 31, 2018
Organization, Consolidation and Presentation of Financial Statements [Abstract]
NATURE OF THE BUSINESS AND OPERATIONS	NATURE OF THE BUSINESS AND OPERATIONS Acacia Communications, Inc. was incorporated on June 2, 2009 , as a Delaware corporation. Acacia Communications, Inc. and its wholly-owned subsidiaries (the “Subsidiaries”) are collectively referred to as the Company. The Company is a leading provider of high-speed coherent optical interconnect products that transform communications networks, relied upon by cloud infrastructure operators and content and communication service providers, through improvements in performance and capacity and reductions in associated costs. The Company’s products include a family of low-power coherent digital signal processors and silicon photonic integrated circuits that it has integrated into families of optical interconnect modules with transmission speeds ranging from 100 to 400 gigabits per second for use in long-haul, metro and inter-data center markets. The Company is also developing its AC1200 module that will enable, across dual wavelengths, transmission capacity of 1.2 terabits (1,200 gigabits) per second and above. The Company is headquartered in Maynard, Massachusetts, and has established wholly-owned subsidiaries in North America, Europe and Asia as part of the Company’s global expansion.

BASIS OF PRESENTATION AND SUMMA

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES The unaudited condensed consolidated financial statements include the accounts of Acacia Communications, Inc. and its Subsidiaries and have been prepared in accordance with accounting principles generally accepted in the United States of America (“GAAP”) and pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). Accordingly, they do not include all of the information and footnotes required by GAAP for annual financial statements. For further information, these condensed consolidated financial statements should be read in conjunction with the audited consolidated financial statements and related notes contained in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 , which was filed with the SEC on February 22, 2018. There have been no significant changes in the Company’s accounting policies from those disclosed in the Annual Report on Form 10-K that have had a material impact on the Company’s condensed consolidated financial statements. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited consolidated financial statements as of and for the year ended December 31, 2017 , and in management’s opinion, include all adjustments, consisting of only normal recurring adjustments, necessary for the fair statement of the Company’s condensed consolidated balance sheet as of March 31, 2018 , its condensed consolidated statements of operations for the three months ended March 31, 2018 and 2017 , its condensed consolidated statements of comprehensive (loss) income for the three months ended March 31, 2018 and 2017 , its condensed consolidated statements of stockholders’ equity for the three months ended March 31, 2018 and 2017 , and its condensed consolidated statements of cash flows for the three months ended March 31, 2018 and 2017 . All intercompany balances and transactions have been eliminated in consolidation. The financial data and the other financial information disclosed in the notes to these condensed consolidated financial statements related to these three -month periods are also unaudited. The results of operations for the three months ended March 31, 2018 are not necessarily indicative of the results to be expected for the full fiscal year or any other period. Use of Estimates The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates. Reclassifications Certain prior period amounts have been reclassified to conform to the current period presentation. Specifically, as of December 31, 2017, $0.2 million of deferred product costs have now been included within “Prepaid expenses and other current assets” on the condensed consolidated balance sheet, and for the three months ended March 31, 2017 , the $0.2 million increase in deferred product costs has now been included within the increase in “Prepaid expenses and other current assets” on the condensed consolidated statement of cash flows. Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASC 606”) which supersedes the revenue recognition requirements in Accounting Standard Codification 605, Revenue Recognition (“ASC 605”) and affects any entity that enters into contracts with customers to transfer goods and services. On January 1, 2018, the Company adopted ASC 606 and all related amendments for all contracts not completed as of the adoption date using the modified retrospective method. The Company recognized the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of retained earnings. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. In accordance with ASC 606, the Company recognizes revenue under the core principle to depict the transfer of control to the Company’s customers in an amount reflecting the consideration the Company expects to be entitled. In order to achieve that core principle, the Company applies the following five step approach: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract and (5) recognize revenue when a performance obligation is satisfied. Revenue for product sales is recognized at the point in time when control transfers to the Company’s customers, which is generally when products are shipped from the Company’s manufacturing facilities or when delivered to the customer’s named location. When the Company performs shipping and handling activities after the transfer of control to the customer (e.g., when control transfers prior to delivery), they are considered to be fulfillment activities, and accordingly, the costs are accrued for when the related revenue is recognized. Taxes collected from customers relating to product sales and remitted to governmental authorities are excluded from revenue. See Note 3 for further disclosures and detail regarding revenue. As the impact of ASC 606 is not material to the Company, there is no pro-forma disclosure presented as of and for the quarter ended March 31, 2018. The Company expects the impact of the adoption of the new standard to be immaterial to its results of operations on an ongoing basis. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory (“ASU 2016-16”). ASU 2016-16 requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The amendments in ASU 2016-16 are effective for fiscal years beginning after December 15, 2017, and were adopted by the Company in the first quarter of 2018. The amendments in ASU 2016-16 have been applied using a modified retrospective approach. As the Company has not had any intra-entity transfers of assets in such period other than inventory, there is no impact from the adoption of this standard. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash (“ASU 2016-18”) . The amendments in ASU 2016-18 require that the statement of cash flows explain the change in total cash, cash equivalents and restricted cash. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company has adopted the amendments in ASU 2016-18 in the first quarter of 2018 using a retrospective transition method. Other than the revised statement of cash flows presentation of restricted cash in the prior period presented, which was immaterial, the adoption of ASU 2016-18 did not have a material impact on the Company’s condensed consolidated financial statements for the three months ended March 31, 2017 . There is no impact to the cash flow statement for the three months ended March 31, 2018 as there was no restricted cash balance as of the beginning or end of the period. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 is intended to provide more decision-useful information about expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The main provisions include presenting financial assets measured at amortized cost at the amount expected to be collected, which is net of an allowance for credit losses, and recording credit losses related to available-for-sale securities through an allowance for credit losses. The amendments in ASU 2016-13 are effective for fiscal years beginning after December 15, 2019, and must be applied using a modified retrospective approach with earlier adoption permitted for fiscal years beginning after December 15, 2018. The Company is currently evaluating the impact of this guidance on its condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize a right-of-use asset and lease liability on the balance sheet for virtually all leases. For the statement of operations, ASU 2016-02 retains a dual model requiring leases to be classified as either operating or financing leases. Operating leases will result in straight-line expense, and financing leases will have a front-loaded expense pattern with an interest expense component. The amendments in ASU 2016-02 are effective for fiscal years beginning after December 15, 2018, and must be applied using a modified retrospective approach with earlier adoption permitted. The Company expects the adoption of ASU 2016-02 will increase both its assets and liabilities presented on its condensed consolidated balance sheets to reflect the right-of-use assets and corresponding lease liabilities, as well as increase its leasing disclosures. The Company is continuing its assessment and review of existing leases, as well as policy and process changes to support the new standard.

REVENUE

REVENUE	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
REVENUE	REVENUE The Company adopted ASC 606 effective January 1, 2018 using the modified retrospective method. The Company recognized the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of retained earnings. The comparative information is accounted for in accordance with the previous revenue guidance, ASC 605, and has not been restated. Revenue recognized prior to the effective date is accounted for in accordance with the accounting policies disclosed in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2017 . The following are the policies the Company has applied beginning January 1, 2018. The Company generates all of its revenue from contracts with customers. The Company considers customer purchase orders, which in many cases are governed by master purchasing agreements, to be contracts with customers. The Company’s contracts with customers are generally for product only, and do not include other performance obligations such as services, extended warranties or other material rights. As part of its assessment of each contract, the Company evaluates certain factors including the customer’s ability to pay (or credit risk). For each contract, the Company considers the promise to transfer products, each of which is distinct, to be the identified performance obligations. In determining the transaction price, the price stated on the purchase order is typically fixed and represents the net consideration to which the Company expects to be entitled, and therefore there is no variable consideration. As the Company’s standard payment terms are less than one year, the Company has elected, as a practical expedient, to not assess whether a contract has a significant financing component. The Company allocates the transaction price to each distinct product based on its relative standalone selling price. The product price as specified on the purchase order is considered the standalone selling price as it is an observable source that depicts the price as if sold to a similar customer in similar circumstances. Revenue is recognized when control of the product is transferred to the customer (i.e., when the Company’s performance obligation is satisfied), which typically occurs upon shipment from the Company’s manufacturing site or delivery to the customer’s named location. In determining whether control has transferred, the Company considers if there is a present right to payment from the customer and when physical possession, legal title and risks and rewards of ownership have transferred to the customer. The Company also considered certain customer contracts that include acceptance clauses, but has concluded that delivery to the customer’s named location is the point at which the customer is able to direct the use of and obtain substantially all of the remaining benefits from the asset, and therefore the acceptance is considered a formality that does not impact the timing of revenue recognition. At times, the Company receives orders for products that may be delivered over multiple dates that may extend across reporting periods. The Company invoices for each delivery upon shipment and recognizes revenues for each distinct product delivered, assuming transfer of control has occurred. As scheduled delivery dates are within one year, the Company has elected to use the optional exemption whereby revenues allocated to future shipments of partially completed contracts are not disclosed. The Company generally provides an assurance warranty that its products will substantially conform to the agreed-upon specifications for 12 to 24 months from the date of shipment. The Company’s liability is limited to the cost of repair or replacement of the defective part. The Company does not consider activities related to such warranties to be a separate performance obligation. The terms and conditions of sale generally do not allow for refunds or product returns other than for warranty repairs. The Company has a limited number of customer contracts that provide for the performance of services or include multiple performance obligations. Once the Company determines the performance obligations, the Company determines the transaction price, which includes estimating the amount of variable consideration to be included in the transaction price, if any. The Company then allocates the transaction price to each performance obligation in the contract based on a relative stand-alone selling price method or using the variable consideration allocation exception if the required criteria are met. The corresponding revenues are recognized as the related performance obligations are satisfied. A receivable is recognized in the period the Company ships the product. Payment terms on invoiced amounts are typically 30 - 60 days. In some cases, if control of the product has not yet transferred to the customer or the timing of the payments made by the customer precedes the Company’s fulfillment of the performance obligation, the Company recognizes a contract liability that is classified as “deferred revenue.” The opening and closing balances of the Company’s deferred revenue and accounts receivable are as follows (in thousands): Balance at Beginning of Period (1/1/18) (Decrease) / Increase Balance at End of Period Three Months Ended March 31, 2018 Accounts Receivable $ 86,602 (11,837 ) $ 74,765 Deferred Revenue (Current) $ 197 1,163 $ 1,360 Deferred Revenue (Non-current) $ 254 2,196 $ 2,450 The amounts of revenue recognized in the period that were included in the opening deferred revenue balance was immaterial for the three months ended March 31, 2018 . The increase in current and non-current deferred revenue is related to billings to, or advance payments from, customers for which the Company has not yet fulfilled its performance obligations. Deferred revenue not expected to be recognized within the Company’s operating cycle of one year is presented as a component of “Other long-term liabilities” on the condensed consolidated balance sheet. The Company has concluded that none of the costs it has incurred to obtain and fulfill its ASC 606 contracts meet the capitalization criteria, and as such, there are no costs deferred and recognized as assets on the condensed consolidated balance sheet. Disaggregation of Revenue The following table provides information about disaggregated revenue based on the geographic region of the Company’s customers’ ship-to destinations, which in certain instances may be the location of a contract manufacturer rather than the Company’s end customer. Further disaggregation of revenue by geographic country can be found in Note 12. Three Months Ended As a % of March 31, 2018 Total Revenue (dollars in thousands) Americas $ 9,725 13 % EMEA 27,644 38 % APAC 35,572 49 % Total revenue $ 72,941 100 %

FINANCIAL INSTRUMENTS

FINANCIAL INSTRUMENTS	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
FINANCIAL INSTRUMENTS	FINANCIAL INSTRUMENTS The following tables set forth the Company’s cash, cash equivalents and short- and long-term marketable securities as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Gross Unrealized Losses Amortized Cost Gains Less than One Year Greater than One Year Estimated Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 52,831 $ — $ — $ — $ 52,831 $ 52,831 $ — Money market funds 8,907 — — — 8,907 8,907 — Repurchase agreements 13,700 — — — 13,700 13,700 — U.S. treasury bonds 31,346 — (99 ) — 31,247 4,999 26,248 Commercial paper 49,141 — (29 ) — 49,112 — 49,112 Certificates of deposit 49,524 6 (107 ) — 49,423 1,700 47,723 Asset-backed securities 40,896 1 (151 ) — 40,746 2,998 37,748 Corporate debt securities 122,100 5 (560 ) (5 ) 121,540 — 121,540 Total $ 368,445 $ 12 $ (946 ) $ (5 ) $ 367,506 $ 85,135 $ 282,371 December 31, 2017 Gross Unrealized Estimated Cash and Cash Marketable Amortized Cost Gains Losses (1) Fair Value Equivalents Securities Cash $ 43,223 $ — $ — $ 43,223 $ 43,223 $ — Money market funds 11,070 — — 11,070 11,070 — Repurchase agreements 12,500 — — 12,500 12,500 — U.S. treasury bonds 26,316 — (80 ) 26,236 — 26,236 Commercial paper 60,623 — (9 ) 60,614 — 60,614 Certificates of deposit 34,993 6 (33 ) 34,966 — 34,966 Asset-backed securities 33,374 1 (53 ) 33,322 702 32,620 Corporate debt securities 142,960 9 (290 ) 142,679 — 142,679 Total $ 365,059 $ 16 $ (465 ) $ 364,610 $ 67,495 $ 297,115 (1) Losses represent marketable securities that were in loss positions for less than one year. The proceeds from the sales and maturities of marketable securities, which were primarily reinvested and resulted in realized gains and losses, were as follows (in thousands): Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Proceeds from the sales and maturities of marketable securities $ 87,830 $ 38,900 Realized gains $ 4 $ 1 Realized losses $ (2 ) $ — The contractual maturities of short-term and long-term marketable securities held at March 31, 2018 and December 31, 2017 are as follows (in thousands): March 31, 2018 December 31, 2017 Amortized Cost Basis Aggregate Fair Value Amortized Cost Basis Aggregate Fair Value Due within one year $ 223,179 $ 222,540 $ 212,137 $ 211,933 Due after one year through three years 60,131 59,831 85,426 85,182 Total $ 283,310 $ 282,371 $ 297,563 $ 297,115 At March 31, 2018 , the Company believed that the unrealized losses on its available-for-sale investments were temporary. The investments with unrealized losses consisted primarily of corporate debt securities. In making the determination that the decline in fair value of these securities was temporary, the Company considered various factors, including, but not limited to: the length of time each security was in an unrealized loss position; the extent to which fair value was less than cost; the financial condition and near-term prospects of the issuers; and the Company’s intent not to sell these securities and the assessment that it is more likely than not that the Company would not be required to sell these securities before the recovery of their amortized cost basis.

INVENTORY

INVENTORY	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
INVENTORY	INVENTORY Inventory consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Raw materials $ 37,195 $ 32,599 Work-in-process 663 965 Finished goods 19,298 28,668 Inventory $ 57,156 $ 62,232 On April 15, 2018, the U.S. Department of Commerce imposed a seven-year denial of export privileges that restricts sales to ZTE Kangxun Telecom Co. Ltd., or ZTE, the Company’s largest customer. As a result, the Company recorded inventory write-offs of $3.9 million in the three months ended March 31, 2018 related to finished goods inventory that had either been designed specifically for ZTE, or had been intended for consumption by ZTE and is now excess inventory due to the Company’s current suspension of sales to ZTE or ZTE’s future demand for product.

PROPERTY AND EQUIPMENT

PROPERTY AND EQUIPMENT	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
PROPERTY AND EQUIPMENT	PROPERTY AND EQUIPMENT Property and equipment consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Engineering laboratory equipment $ 42,763 $ 39,433 Computer software 2,565 2,281 Computer equipment 4,636 4,380 Furniture and fixtures 3,201 3,041 Leasehold improvements 3,015 2,282 Construction in progress 5,345 4,591 Total property and equipment 61,525 56,008 Less: Accumulated depreciation (31,099 ) (27,833 ) Property and equipment, net $ 30,426 $ 28,175 Depreciation expense was $3.3 million and $2.9 million for the three months ended March 31, 2018 and 2017 , respectively.

ACCRUED LIABILITIES

ACCRUED LIABILITIES	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
ACCRUED LIABILITIES	ACCRUED LIABILITIES Accrued liabilities consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Employee-related liabilities $ 8,095 $ 5,233 Outsourced foundry services 1,345 95 Goods and services received not invoiced 8,815 12,827 Accrued manufacturing related expenses 7,648 4,007 Warranty reserve 7,418 8,306 Other accrued liabilities 9,461 6,766 Accrued liabilities $ 42,782 $ 37,234 Due to the denial order against ZTE discussed in Note 5, the Company recorded $3.2 million of accrued manufacturing reserves as of March 31, 2018 related to non-cancellable commitments to purchase inventory that was either designed specifically for ZTE, or had been intended for consumption by ZTE and is now excess inventory due to the Company’s current suspension of sales to ZTE or ZTE’s future demand for product. Certain prior period amounts have been reclassified to conform to the current period presentation. Specifically, as of December 31, 2017 , $0.4 million of accrued income taxes have now been reclassified to be included within “Other accrued liabilities” in conformity with the current period presentation.

FAIR VALUE MEASUREMENT

FAIR VALUE MEASUREMENT	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
FAIR VALUE MEASUREMENT	FAIR VALUE MEASUREMENT The Company measures certain financial assets and liabilities at fair value. Fair value is determined based upon the exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants, as determined by either the principal market or the most advantageous market. Inputs used in the valuation techniques to derive fair values are classified based on a three-level hierarchy, as follows: Level 1 —Quoted prices (unadjusted) in active markets for identical assets or liabilities. Level 2 —Observable inputs other than Level 1 prices such as quoted prices for similar assets or liabilities, quoted prices in markets with insufficient volume or infrequent transactions (less active markets), or model-derived valuations in which all significant inputs are observable or can be derived principally from or corroborated by observable market data for substantially the full term of the assets or liabilities. Level 3 —Unobservable inputs to the valuation methodology that are significant to the measurement of fair value of assets or liabilities. The Company considers all highly liquid investments purchased with an original maturity of three months or less to be cash equivalents. The Company’s cash equivalents consist of money market funds, repurchase agreements, U.S. government agency debt securities, certificates of deposit and asset-backed securities with an original maturity of three months or less. The Company’s investments in money market funds, repurchase agreements, U.S. government agency debt securities, commercial paper, certificates of deposit, asset-backed securities and corporate debt securities, which are classified as Level 2 within the fair value hierarchy, were initially valued at the transaction price and subsequently valued at each reporting date utilizing market-observable data. The market-observable data included reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The fair value of these assets measured on a recurring basis was determined using the following inputs as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets: Money market funds $ — $ 8,907 $ — $ 8,907 Repurchase agreements — 13,700 — 13,700 U.S. treasury bonds — 31,247 — 31,247 Commercial paper — 49,112 — 49,112 Certificates of deposit — 49,423 — 49,423 Asset-backed securities — 40,746 — 40,746 Corporate debt securities — 121,540 — 121,540 Total $ — $ 314,675 $ — $ 314,675 December 31, 2017 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets: Money market funds $ — $ 11,070 $ — $ 11,070 Repurchase agreements — 12,500 — 12,500 U.S. treasury bonds — 26,236 — 26,236 Commercial paper — 60,614 — 60,614 Certificates of deposit — 34,966 — 34,966 Asset-backed securities — 33,322 — 33,322 Corporate debt securities — 142,679 — 142,679 Total $ — $ 321,387 $ — $ 321,387 There were no transfers between fair value measurement levels during the three months ended March 31, 2018 or 2017 . For certain other financial instruments, including accounts receivable, accounts payable and other current liabilities, the carrying amounts approximate their fair value due to the relatively short maturity of these balances.

STOCK COMPENSATION PLANS

STOCK COMPENSATION PLANS	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
STOCK COMPENSATION PLANS	STOCK COMPENSATION PLANS The following table summarizes the classification of stock-based compensation in the condensed consolidated statements of operations for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Cost of revenue $ 521 $ 442 Research and development 3,788 2,992 Sales, general and administrative 2,229 1,198 Total stock-based compensation $ 6,538 $ 4,632 The following table summarizes stock-based compensation expense by award type for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Stock options $ 601 $ 666 Restricted stock units 5,595 3,686 Employee stock purchase plan 298 251 Other awards 44 29 Total stock-based compensation $ 6,538 $ 4,632 Stock Options A summary of stock option activity under the Company’s equity incentive plans for the three months ended March 31, 2018 is as follows: Number of Options (in thousands) Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 1,634 $ 8.34 6.6 $ 47,356 Granted — $ — Exercised (220 ) $ 4.40 $ 7,660 Cancelled (25 ) $ 11.95 Outstanding at March 31, 2018 1,389 $ 8.90 6.4 $ 42,655 Vested at: March 31, 2018 1,389 $ 8.90 6.4 $ 42,655 December 31, 2017 1,634 $ 8.34 6.6 $ 47,356 Exercisable at: March 31, 2018 808 $ 5.91 5.8 $ 26,919 December 31, 2017 907 $ 5.28 5.9 $ 28,634 As of March 31, 2018 and December 31, 2017 , there was $4.1 million and $4.8 million , respectively, of unrecognized compensation cost related to unvested common stock options which is expected to be recognized over weighted-average periods of 1.9 years and 2.2 years, respectively. No stock option awards were issued by the Company during the three months ended March 31, 2018 or 2017 . Restricted Stock Units During the three months ended March 31, 2018 , the Company granted approximately 497,000 restricted stock units (“RSUs”) to employees and executives under the 2016 Equity Incentive Plan that vest upon the satisfaction of a service condition, generally over four years. The cost of any RSUs with only a service condition is determined using the fair value of the Company’s common stock on the date of grant, and compensation is recognized on a straight-line basis over the requisite vesting period. During the three months ended March 31, 2018 , the Company granted awards covering up to a maximum of 90,808 performance-based RSUs to executive officers that include a market condition in addition to a service condition (“performance-based RSUs” or “PRSUs”). Each PRSU represents the right to receive one share of the Company’s common stock when and if the applicable vesting conditions are satisfied. The PRSUs are subject to performance-based vesting. The number of PRSUs that vest is measured based on the level of achievement of a performance objective over a three -year period (the “Performance Period”) running from January 1, 2018 through December 31, 2020, as determined and certified by the Compensation Committee of the Board of Directors following the end of the Performance Period. The level of achievement will be determined based on the Company’s percentile achievement of relative total shareholder returns against an external comparator group during the Performance Period (the “Relative TSR Objective”). Vesting of the PRSUs is also subject to the applicable officer’s continued provision of services to the Company through the vesting date, except in the case of death or disability where vesting will be pro rated for time worked during the Performance Period. No PRSUs will vest unless a threshold level of achievement of the Relative TSR Objective is achieved. The Company estimated the fair value of the PRSUs using a Monte Carlo valuation model on the date of grant, using the following assumptions: Risk-free interest rate 2.3% Expected dividend yield None Expected volatility 51.4% Expected term (in years) 2.9 Grant date fair value of underlying shares $39.02 As soon as practicable following each vesting date of RSUs, including PRSUs, the Company will issue to the holder of the RSUs the number of shares of common stock equal to the aggregate number of RSUs that have vested. Notwithstanding the foregoing, the Company may, in its sole discretion, in lieu of issuing shares of common stock to the holder of the RSUs, pay the holder an amount in cash equal to the fair market value of such shares of common stock. To date, the Company has not settled any vested RSUs with cash. A summary of the changes in the Company’s RSUs during the three months ended March 31, 2018 is as follows: RSUs (in thousands) Weighted-Average Grant Date Fair Value Outstanding at December 31, 2017 2,288 $ 36.08 Granted 588 $ 43.20 Vested (214 ) $ 34.69 Cancelled (11 ) $ 25.92 Outstanding at March 31, 2018 2,651 $ 37.81 The granted amount includes the 90,808 PRSUs which is the maximum number that were granted to executives during the three months ended March 31, 2018 . As of March 31, 2018 and December 31, 2017 , there was $64.8 million and $47.8 million , respectively, of total unrecognized compensation cost related to unvested RSUs which is expected to be recognized over weighted-average periods of 3.1 years and 2.9 years, respectively.

NET (LOSS) INCOME PER SHARE

NET (LOSS) INCOME PER SHARE	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
NET (LOSS) INCOME PER SHARE	NET (LOSS) INCOME PER SHARE The following table sets forth the computation of the Company’s basic and diluted net (loss) income per share (in thousands, except per share amounts): Three Months Ended March 31, 2018 2017 Numerator: Net (loss) income $ (9,078 ) $ 35,709 Denominator: Weighted-average shares used to compute net (loss) income per share - basic 39,836 38,308 Dilutive effect of stock options, unvested restricted stock and restricted stock units and employee stock purchase plan — 3,346 Weighted-average shares used to compute net (loss) income per share - diluted 39,836 41,654 Net (loss) income per share Basic $ (0.23 ) $ 0.93 Diluted $ (0.23 ) $ 0.86 The following common stock equivalents (in thousands) were excluded from the computation of diluted net (loss) income per share for the periods presented because including them would have been antidilutive: Three Months Ended March 31, 2018 2017 Options to purchase common stock 1,218 49 Unvested restricted stock units and awards 1,445 152 Employee stock purchase plan 3 — As discussed further in Note 9, in February 2018, the Company granted a maximum of 90,808 PRSUs to executives that include a market condition and service conditions. An estimate of the number of shares contingently issuable based on average market prices through March 31, 2018 has been included in the antidilutive table above.

COMMITMENTS AND CONTINGENCIES

COMMITMENTS AND CONTINGENCIES	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
COMMITMENTS AND CONTINGENCIES	COMMITMENTS AND CONTINGENCIES Leases The Company’s principal facilities are located in Maynard, Massachusetts and Holmdel, New Jersey and are leased by the Company under non-cancelable operating leases that expire in February 2025, with respect to the Massachusetts facility, and January 2022, with respect to the New Jersey facility. The Company also leases office space in various locations with expiration dates between 2018 and 2021 . Several of the lease agreements include leasehold improvement incentives, escalating lease payments, renewal provisions and other provisions which require the Company to pay taxes, insurance and maintenance costs. All of the Company’s facility leases are accounted for as operating leases. Rent expense is recorded over each respective lease term on a straight-line basis. Rent expense was $1.2 million and $1.5 million for the three months ended March 31, 2018 and 2017 , respectively. Future minimum lease payments due under these non-cancelable lease agreements as of March 31, 2018 , are as follows (in thousands): Amounts Remaining 2018 $ 2,481 2019 3,311 2020 3,339 2021 3,235 2022 2,415 Thereafter 5,393 Total $ 20,174 Warranties The Company’s standard warranty obligation to its customers provides for repair or replacement of a defective product at the Company’s discretion for a period of time following purchase, generally between 12 and 24 months . Factors that affect the warranty obligation include product failure rates, material usage and service delivery costs incurred in correcting product failures. In addition, from time to time, specific warranty accruals may be made if unforeseen technical problems arise. The estimated cost associated with fulfilling the Company’s warranty obligation to customers is recorded in cost of revenue. In May 2017, the Company announced a quality issue at one of its three contract manufacturers (the “Quality Issue”) that affected a portion of the units manufactured by the contract manufacturer over an approximate four month period, which is estimated at approximately 1,300 AC400 units and 5,100 CFP units under warranty. Based on the ongoing evaluation of such units, the Company established reserves to cover anticipated costs, including cost estimates for product repairs, rework of component inventory with the contract manufacturer and rescreening costs associated with this Quality Issue. These costs are estimated based on the results of testing performed to date, which is ongoing, in addition to yield, fall-out rates and component part recovery cost estimates based on the Company’s historical experience. The Company’s estimates of the Quality Issue costs are subject to further change as customers continue to return potentially impacted units and final testing is performed. Changes in the Company’s warranty liability, which is included as a component of accrued liabilities on the condensed consolidated balance sheets, are set forth in the table below (in thousands): Three Months Ended March 31, 2018 2017 Warranty reserve, beginning of period $ 8,306 $ 2,158 Provisions made to warranty reserve during the period 3,463 1,138 Charges against warranty reserve during the period (4,351 ) (1,183 ) Warranty reserve, end of period $ 7,418 $ 2,113 Legal Contingencies On January 21, 2016, ViaSat, Inc. filed a suit against the Company alleging, among other things, breach of contract, breach of the implied covenant of good faith and fair dealing and misappropriation of trade secrets. On February 19, 2016, the Company responded to ViaSat’s suit and alleged counterclaims against ViaSat including, among other things, patent misappropriation, breach of contract, breach of the implied covenant of good faith and fair dealing, misappropriation of trade secrets and unfair competition, which ViaSat denied in its response filed March 16, 2016. The Company is continuing to evaluate ViaSat’s claims, but based on the information available to the Company today, the Company currently believes that this suit will not have a material adverse effect on the Company’s business or its consolidated financial position, results of operations or cash flows. On July 28, 2017, the Company filed a suit against ViaSat asserting commercial disparagement, libel, slander of title, unfair competition, intentional interference with advantageous relations and intentional interference with contractual relations. Both lawsuits are still pending, and discovery is closed in the 2016 action filed by ViaSat and ongoing in the 2017 action. In August and September 2017, three purported securities class action complaints were filed in the United States District Court for the District of Massachusetts against the Company and certain of its executive officers (Murugesan Shanmugaraj and John Gavin). The complaints are captioned Tharp v. Acacia Communications, Inc., et al. , Case No. 1:17-cv-11504 (D. Mass.), filed August 14, 2017; Zhang v. Acacia Communications, Inc., et al. , Case No. 1:17-cv-11518 (D. Mass.), filed August 16, 2017; and Kebler v. Acacia Communications, Inc., et al. , Case No. 1:17-cv-11695 (D. Mass.), filed September 7, 2017. Each complaint purports to be brought on behalf of an alleged class of those who purchased the Company’s securities between August 11, 2016 and July 13, 2017, and alleges that the defendants violated Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder by making allegedly false and/or misleading statements regarding, among other matters, demand for the Company’s products, the Company’s financial guidance, and/or the Company’s quality control process as it relates to the Quality Issue. Each complaint seeks, among other relief, unspecified compensatory damages, attorneys’ fees, and costs. On October 13, 2017, a fourth purported securities class action complaint was filed in the United States District Court for the District of Massachusetts against the Company, certain of its directors and executive officers (Murugesan Shanmugaraj, John Gavin, Francis Murphy, Eric Swanson, Peter Chung, Benny Mikkelsen, Stan Reiss, John Ritchie, Vincent Roche, Mehrdad Givehchi, John LoMedico, Bhupendra Shah and Christian Rasmussen), certain persons or entities that sold the Company’s common stock in the Company’s October 2016 follow-on public offering, and the underwriters of such offering, captioned Rollhaus v. Acacia Communications, Inc., et al. , Case No. 17-cv-11988 (D. Mass). The complaint purports to be brought on behalf of an alleged class of those who purchased the Company’s common stock pursuant to or traceable to the follow-on offering, and alleges that the defendants violated Sections 11, 12(a)(2) and/or 15 of the Securities Act of 1933 by making allegedly false and/or misleading statements regarding, among other matters, demand for the Company’s products, the Company’s financial guidance, and/or the Company’s quality control process as it relates to the Quality Issue. The complaint seeks, among other relief, unspecified compensatory damages, rescission, attorneys’ fees, and costs. On November 7, 2017, the court consolidated these four securities class actions (under docket number 1:17-cv-11504). On November 9, 2017, the court appointed lead plaintiffs for the consolidated action. Lead plaintiffs filed a consolidated amended class action complaint on January 8, 2018. The amended complaint makes allegations similar to those in the original four complaints, against the same defendants, and alleges that some or all of the defendants violated Sections 11, 12(a)(2) and/or 15 of the Securities Act of 1933 and Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder. All defendants filed motions to dismiss the consolidated amended complaint on February 9, 2018. The court held a hearing on the motions to dismiss on March 29, 2018, afforded the plaintiffs an additional 30 days to file a motion for leave to file a further amended complaint, and took the motions to dismiss under advisement. On April 30, 2018, plaintiffs filed a motion for leave to amend the complaint. The proposed amended complaint makes allegations similar to those in the consolidated amended complaint, asserts claims against the Company, certain of its directors and executive officers (Murugesan Shanmugaraj, John Gavin, Francis Murphy, Eric Swanson, Peter Chung, Benny Mikkelsen, Stan Reiss, John Ritchie and Vincent Roche), certain entities that sold the Company’s common stock in its October 2016 follow-on public offering, and the underwriters of such offering, and alleges that some or all of the defendants violated Sections 11, 12(a)(2) and/or 15 of the Securities Act of 1933 and Sections 10(b) and/or 20(a) of the Securities Exchange Act of 1934 and Rule 10b-5 promulgated thereunder. Defendants’ responses to plaintiffs’ motion for leave to amend are due on May 14, 2018. In November and December 2017, three purported shareholder derivative lawsuits were filed in the United States District Court for the District of Massachusetts against certain of the Company’s directors and executive officers (Murugesan Shanmugaraj, John Gavin, Francis Murphy, Eric Swanson, Peter Chung, Benny Mikkelsen, Stan Reiss, John Ritchie, Vincent Roche, Mehrdad Givehchi, Bhupendra Shah and Christian Rasmussen) and the Company as a nominal defendant. A fourth purported shareholder derivative lawsuit was filed against the same defendants in the same court on March 13, 2018. The complaints are captioned Colgan v. Shanmugaraj et al. , Case No. 1:17-cv-12350 (D. Mass.), filed November 29, 2017; Wong v. Shanmugaraj et al. , Case No. 1:17-cv-12550 (D. Mass.), filed December 22, 2017; Dennis v. Shanmugaraj et al. , Case No. 1:17-cv-12571 (D. Mass.), filed December 28, 2017; and Farah-Franco et al. v. Shanmugaraj et al. , Case No. 1:18-cv-10465 (D. Mass), filed March 13, 2018. The court has consolidated these complaints with the class actions (under docket number 1:17-cv-11504). Each complaint generally alleges that the individual defendants breached fiduciary duties owed to the Company by making or causing the Company to make allegedly false and/or misleading statements regarding, among other matters, demand for the Company’s products, the Company’s financial guidance, and/or the Company’s quality control process as it relates to the Quality Issue. The complaints also allege that certain individual defendants caused the Company to issue an allegedly false and/or misleading proxy statement on or about April 6, 2017 regarding, among other matters, the reelection of certain directors. The complaints purport to assert derivative claims for violation of Sections 14(a) and 29(b) of the Securities Exchange Act of 1934, breach of fiduciary duty, waste of corporate assets, unjust enrichment, abuse of control and/or gross mismanagement, and seek to recover on behalf of the Company for any liability it incurs as a result of the individual defendants’ alleged misconduct. The complaints seek declaratory, equitable and monetary relief, restitution, and attorneys’ fees and costs. The plaintiffs in these actions have filed motions for appointment of lead plaintiff and/or lead counsel. On April 20, 2018, the plaintiffs submitted a stipulation (subject to court approval) regarding the appointment of lead plaintiffs and lead counsel and proposing a schedule for the submission of a consolidated amended complaint and defendants’ response thereto. On April 9, 2018, a purported shareholder filed a complaint against the Company in the Court of Chancery of the State of Delaware seeking to inspect certain books and records of the Company pursuant to 8 Del. C. §220. The complaint is captioned Silberberg v. Acacia Communications, Inc. , Case No. 2018-0262-TMR (Del. Ch.). The plaintiff seeks production of documents regarding, among other matters, demand for the Company’s products, its financial guidance, its quality control process as it relates to the Quality Issue, and the Company’s October 2016 follow-on public offering. The plaintiff filed a motion for expedited proceedings, and the parties reached agreement on a case schedule. The Company filed its answer on April 27, 2018. The plaintiff filed his motion for judgment on the pleadings on May 1, 2018, the Company’s cross-motion for judgment on the pleadings and opposition is due May 11, 2018, and any reply is due May 16, 2018. The Court will hold a telephonic hearing on these motions on May 29, 2018. The Company intends to engage in a vigorous defense of the litigation described above. However, the Company is unable to predict the ultimate outcome of these proceedings, and, therefore cannot estimate possible losses or ranges of losses, if any, or the materiality of any such losses. An unfavorable resolution of these matters in any reporting period may have a material adverse effect on the Company’s results of operations and cash flows for that period. In addition, the timing of the final resolution of these proceedings is uncertain. The Company will incur litigation and other expenses as a result of these proceedings, which could have a material impact on the Company’s business, consolidated financial position, results of operations and cash flows. In addition, from time to time the Company may become involved in legal proceedings or be subject to claims arising in the ordinary course of its business. Although the results of litigation and claims cannot be predicted with certainty, the Company currently believes that the final outcome of these ordinary course matters will not have a material adverse effect on the Company’s business or on its consolidated financial position, results of operations or cash flows. Regardless of the outcome, litigation can have an adverse impact on the Company because of defense and settlement costs, diversion of management resources and other factors. Indemnification In the ordinary course of business, the Company enters into various agreements containing standard indemnification provisions. The Company’s indemnification obligations under such provisions are typically in effect from the date of execution of the applicable agreement through the end of the applicable statute of limitations. During the three months ended March 31, 2018 and 2017 , the Company did not experience any losses related to these indemnification obligations. The Company does not expect significant claims related to these indemnification obligations, and consequently, has concluded that the fair value of these obligations is not material. Accordingly, as of March 31, 2018 and December 31, 2017 , no amounts have been accrued related to such indemnification provisions.

INCOME TAXES

INCOME TAXES	3 Months Ended
	Mar. 31, 2018
Income Tax Disclosure [Abstract]
INCOME TAXES	INCOME TAXES The U.S. Tax Cuts and Jobs Act (the “Act”) was enacted on December 22, 2017. Among other changes, this legislation: (1) reduces the U.S. federal corporate tax rate from 35% to 21%; (2) requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax-deferred; (3) creates new taxes on certain foreign sourced earnings; (4) provides a general elimination of U.S. federal income taxes on dividends from foreign subsidiaries; (5) includes a new provision designed to currently tax certain global intangible low-taxed income (“GILTI”) of controlled foreign corporations, which allows for the possibility of using foreign tax credits (“FTCs”) and a deduction of up to 50 percent to reduce this income tax liability (subject to some limitations); (6) provides limitations on the use of FTCs to reduce the U.S. income tax liability from GILTI; and (7) provides limitations on net operating losses generated in the taxable years beginning after December 31, 2017, to 80 percent of taxable income. Accounting Standard Codification (“ASC”) 740 requires filers to record the effect of tax law changes in the period enacted. However, the SEC issued Staff Accounting Bulletin No. 118 (“SAB 118”), that permits filers to record provisional amounts during a measurement period ending no later than one year from the date of the Act’s enactment. As of March 31, 2018 , the Company has not completed the accounting for the tax effects of enactment of this legislation; however, the Company has made a reasonable estimate of the effects on its existing deferred tax balances, the one-time transition tax and provisional state taxes on future repatriations. For the items for which the Company was able to determine a reasonable estimate, the Company recognized a provisional amount of $31.4 million under SAB 118 as a component of income tax expense in the year ended December 31, 2017 . The Company is subject to income tax in the United States as well as other tax jurisdictions in which it conducts business. Earnings from non-U.S. activities are subject to local country income tax. As a result of the “deemed distributions” under the Act, the impact of GILTI on the Company’s future foreign earnings and lack of certain foreign governments’ withholding tax imposed on dividends, the Company no longer takes the position that its foreign earnings are permanently reinvested except for limited cases where foreign earnings are required to meet working capital needs. The Company’s tax provision for interim periods is determined using an estimate of its annual effective tax rate, adjusted for discrete items arising in that quarter. In each quarter, the Company updates its estimate of the annual effective tax rate, and if the estimated annual tax rate changes, the Company makes a cumulative adjustment in that quarter. The Company’s quarterly tax provision, and its quarterly estimate of its annual effective tax rate, are subject to significant volatility due to several factors, including the Company’s ability to accurately predict its pre-tax income and loss in multiple jurisdictions, as well as the portions of stock-based compensation that will either not generate tax benefits or the tax benefit is unpredictable and reflected when realized by employees. For the three months ended March 31, 2018 , the Company recorded a benefit from income taxes of $4.3 million as compared to $5.4 million for the three months ended March 31, 2017 , resulting in an effective tax rate of 32.1% and (17.9)% for the three months ended March 31, 2018 and 2017 , respectively. The benefit from income taxes recorded in the three months ended March 31, 2018 is primarily a result of the recognition of excess tax benefits from the taxable compensation on share-based awards recognized in the three months ended March 31, 2018 and federal and state research and development credits. The benefit from income taxes recorded in the three months ended March 31, 2017 was primarily a result of the recognition of excess tax benefits from the taxable compensation on share-based awards recognized in the three months ended March 31, 2017 and the favorable effect of foreign statutory tax rates applicable to income earned outside the United States under the Company’s corporate structure. The Company’s historical (benefit) provision for income taxes is not necessarily reflective of its future results of operations. As of March 31, 2018 and December 31, 2017 , the Company identified $4.8 million and $4.5 million , respectively, of gross uncertain tax positions. Included in those balances as of March 31, 2018 and December 31, 2017 are $2.4 million and $2.3 million , respectively, of tax benefits that, if recognized, would impact the effective tax rate. These have been accrued for as long-term liabilities on the Company’s condensed consolidated balance sheets. The Company’s existing tax positions will continue to generate an increase in unrecognized tax benefits in subsequent periods. The Company’s policy is to record interest and penalties related to unrecognized tax benefits as income tax expense. During the three months ended March 31, 2018 and 2017 , the amounts recorded related to the accrual of interest and penalties were immaterial in each period.

SEGMENT INFORMATION AND GEOGRAP

SEGMENT INFORMATION AND GEOGRAPHIC DATA	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
SEGMENT INFORMATION AND GEOGRAPHIC DATA	SEGMENT INFORMATION AND GEOGRAPHIC DATA The Company operates as one operating segment. Operating segments are defined as components of an enterprise for which separate financial information is regularly evaluated by the chief operating decision maker (“CODM”), which is the Company’s president and chief executive officer, in deciding how to allocate resources and assess performance. The Company’s CODM evaluates the Company’s financial information and resources and assesses the performance of these resources on a consolidated basis. Since the Company operates in one operating segment, all required financial segment information can be found in the condensed consolidated financial statements. Revenue by geographic region, based on ship-to destinations, which in certain instances may be the location of a contract manufacturer rather than the Company’s end customer, was as follows (in thousands): Three Months Ended March 31, 2018 2017 United States $ 9,427 $ 12,414 China 22,083 56,982 Germany 19,746 12,966 Thailand 7,119 11,604 Other 14,566 20,701 Total revenue $ 72,941 $ 114,667 Total long-lived assets by geographic region consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 United States $ 20,866 $ 19,065 China 1,204 1,165 Thailand 6,271 7,065 Other 2,085 880 Total long-lived assets $ 30,426 $ 28,175

CONCENTRATIONS OF RISK

CONCENTRATIONS OF RISK	3 Months Ended
	Mar. 31, 2018
Risks and Uncertainties [Abstract]
CONCENTRATIONS OF RISK	CONCENTRATIONS OF RISK Customer Concentration Customers with revenue equal to or greater than 10% of total revenue for the three months ended March 31, 2018 and 2017 were as follows: Three Months Ended March 31, 2018 2017 A (1) 20 % 41 % B 17 % 11 % C 20 % * * Less than 10% of revenue in the period indicated (1) Customer A is currently subject to U.S. Department of Commerce restrictions that prevent sales to this customer after April 15, 2018. Refer to Note 16 for additional information. Customers that accounted for equal to or greater than 10% of accounts receivable at March 31, 2018 and December 31, 2017 were as follows: March 31, 2018 December 31, 2017 A (1) 24 % 15 % B * 10 % C 21 % 19 % * Less than 10% of accounts receivable at the date indicated (1) Customer A is currently subject to U.S. Department of Commerce restrictions that prevent sales to this customer after April 15, 2018. To date, the Company has concluded that Customer A’s receivable balances as of March 31, 2018 are collectible. The Company will continue to evaluate collectibility of Customer A’s receivable balances. Refer to Note 16 for additional information. Supplier Concentration The Company’s most significant vendor spending is related to purchases from contract manufacturers and component suppliers located in Japan, China, Thailand and the United States, from which the Company purchases a substantial portion of its inventory. For the three months ended March 31, 2018 and 2017 , total purchases from each of the suppliers were as follows: Three Months Ended March 31, 2018 2017 W * 40 % X 22 % * Y 48 % 41 % Z * 10 % * Less than 10% of total purchases in the period indicated The Company also outsources certain engineering projects to vendors located throughout the world. During the three months ended March 31, 2018 the Company incurred 12% of its total research and development costs with Vendor A. During the three months ended March 31, 2017 the Company incurred less than 10% of its total research and development costs with Vendor A.

RELATED PARTIES

RELATED PARTIES	3 Months Ended
	Mar. 31, 2018
Related Party Transactions [Abstract]
RELATED PARTIES	RELATED PARTIES One of the members of the Company’s Board of Directors, Vincent Roche, is also the President and Chief Executive Officer and a member of the board of directors of Analog Devices, Inc. (“ADI”). The Company, through its contract manufacturers, periodically purchases supplies from ADI pursuant to purchase orders negotiated on an arm’s length basis between ADI and the Company’s contract manufacturers at prevailing prices. These purchased supplies are used as content in certain of the Company’s manufactured products. During the three months ended March 31, 2018 and 2017 , the Company’s contract manufacturers made purchases from ADI of approximately $0.7 million and $1.2 million , respectively. In February 2018, the Company entered into a product development agreement with ADI related to the development of integrated circuits for approximately $2.0 million , of which approximately $0.5 million of costs were incurred during the three months ended March 31, 2018 . One of the members of the Company’s Board of Directors, Peter Y. Chung, is also a member of the board of directors of M/A-COM Technology Solutions, Inc. (“MACOM”). The Company, through its contract manufacturers, periodically purchases supplies from MACOM. These purchased supplies are used as content in certain of the Company’s manufactured products. Based on shipments, the Company’s contract manufacturers made purchases from MACOM of approximately $0.3 million for the three months ended March 31, 2018 . The amount of purchases made by the Company from MACOM were immaterial in the three months ended March 31, 2017 .

SUBSEQUENT EVENTS

SUBSEQUENT EVENTS	3 Months Ended
	Mar. 31, 2018
Subsequent Events [Abstract]
SUBSEQUENT EVENTS	SUBSEQUENT EVENTS ZTE On April 15, 2018, the U.S. Department of Commerce imposed a seven-year denial of export privileges that restricts sales to ZTE, the Company’s largest customer, which comprised 20% of revenues during the three months ended March 31, 2018 . The Company considered this to be a recognized subsequent event that provided additional evidence about conditions that existed as of March 31, 2018 . Accordingly, the Company recorded inventory write-offs and reserves of $7.1 million in the three months ended March 31, 2018 related to inventory that had either been designed specifically for ZTE, or had been intended for consumption by ZTE and is now excess inventory due to the Company’s current suspension of sales to ZTE or ZTE’s future demand for product. Further, as of March 31, 2018 , ZTE had a receivable balance of $17.6 million , which has been partially paid to date. Additional payments are expected during the three month period ended June 30, 2018, however the Company is continuing to monitor the collectibility of the receivable balance for any changes in facts or circumstances. Stock Repurchase Program On April 30, 2018, the Company’s Board of Directors authorized the repurchase of up to $60.0 million of the Company’s common stock. Unless terminated earlier by resolution of the Board of Directors, the stock repurchase program will expire on December 31, 2018. The timing and amount of any shares repurchased will be determined by the Company in its discretion and will depend on a number of factors, including market conditions, applicable legal requirements, the Company’s capital needs and alternative uses of capital, among others. The program does not obligate the Company to acquire any specific number of shares. Under the program, shares may be repurchased in open market and/or privately negotiated transactions, including under plans complying with Rule 10b5-1 under the Securities Exchange Act of 1934, as amended.

BASIS OF PRESENTATION AND SUM26

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	3 Months Ended
	Mar. 31, 2018
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The preparation of unaudited condensed consolidated financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the unaudited condensed consolidated financial statements and the reported amounts of revenue and expenses during the reporting period. Actual results could differ from those estimates.
Reclassifications	Reclassifications Certain prior period amounts have been reclassified to conform to the current period presentation.
Recently Adopted and Recently Issued Accounting Pronouncements	Recently Adopted Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standard Update (“ASU”) 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASC 606”) which supersedes the revenue recognition requirements in Accounting Standard Codification 605, Revenue Recognition (“ASC 605”) and affects any entity that enters into contracts with customers to transfer goods and services. On January 1, 2018, the Company adopted ASC 606 and all related amendments for all contracts not completed as of the adoption date using the modified retrospective method. The Company recognized the cumulative effect of initially applying ASC 606 as an adjustment to the opening balance of retained earnings. The comparative information has not been restated and continues to be reported under the accounting standards in effect for those periods. In accordance with ASC 606, the Company recognizes revenue under the core principle to depict the transfer of control to the Company’s customers in an amount reflecting the consideration the Company expects to be entitled. In order to achieve that core principle, the Company applies the following five step approach: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract and (5) recognize revenue when a performance obligation is satisfied. Revenue for product sales is recognized at the point in time when control transfers to the Company’s customers, which is generally when products are shipped from the Company’s manufacturing facilities or when delivered to the customer’s named location. When the Company performs shipping and handling activities after the transfer of control to the customer (e.g., when control transfers prior to delivery), they are considered to be fulfillment activities, and accordingly, the costs are accrued for when the related revenue is recognized. Taxes collected from customers relating to product sales and remitted to governmental authorities are excluded from revenue. See Note 3 for further disclosures and detail regarding revenue. As the impact of ASC 606 is not material to the Company, there is no pro-forma disclosure presented as of and for the quarter ended March 31, 2018. The Company expects the impact of the adoption of the new standard to be immaterial to its results of operations on an ongoing basis. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory (“ASU 2016-16”). ASU 2016-16 requires an entity to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The amendments in ASU 2016-16 are effective for fiscal years beginning after December 15, 2017, and were adopted by the Company in the first quarter of 2018. The amendments in ASU 2016-16 have been applied using a modified retrospective approach. As the Company has not had any intra-entity transfers of assets in such period other than inventory, there is no impact from the adoption of this standard. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows - Restricted Cash (“ASU 2016-18”) . The amendments in ASU 2016-18 require that the statement of cash flows explain the change in total cash, cash equivalents and restricted cash. ASU 2016-18 is effective for fiscal years beginning after December 15, 2017, and interim periods within those fiscal years. The Company has adopted the amendments in ASU 2016-18 in the first quarter of 2018 using a retrospective transition method. Other than the revised statement of cash flows presentation of restricted cash in the prior period presented, which was immaterial, the adoption of ASU 2016-18 did not have a material impact on the Company’s condensed consolidated financial statements for the three months ended March 31, 2017 . There is no impact to the cash flow statement for the three months ended March 31, 2018 as there was no restricted cash balance as of the beginning or end of the period. Recently Issued Accounting Pronouncements In June 2016, the FASB issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (“ASU 2016-13”). ASU 2016-13 is intended to provide more decision-useful information about expected credit losses on financial instruments and other commitments to extend credit held by a reporting entity at each reporting date. The main provisions include presenting financial assets measured at amortized cost at the amount expected to be collected, which is net of an allowance for credit losses, and recording credit losses related to available-for-sale securities through an allowance for credit losses. The amendments in ASU 2016-13 are effective for fiscal years beginning after December 15, 2019, and must be applied using a modified retrospective approach with earlier adoption permitted for fiscal years beginning after December 15, 2018. The Company is currently evaluating the impact of this guidance on its condensed consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (“ASU 2016-02”). ASU 2016-02 will require lessees to recognize a right-of-use asset and lease liability on the balance sheet for virtually all leases. For the statement of operations, ASU 2016-02 retains a dual model requiring leases to be classified as either operating or financing leases. Operating leases will result in straight-line expense, and financing leases will have a front-loaded expense pattern with an interest expense component. The amendments in ASU 2016-02 are effective for fiscal years beginning after December 15, 2018, and must be applied using a modified retrospective approach with earlier adoption permitted. The Company expects the adoption of ASU 2016-02 will increase both its assets and liabilities presented on its condensed consolidated balance sheets to reflect the right-of-use assets and corresponding lease liabilities, as well as increase its leasing disclosures. The Company is continuing its assessment and review of existing leases, as well as policy and process changes to support the new standard.

REVENUE (Tables)

REVENUE (Tables)	3 Months Ended
	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Schedule of Deferred Revenue and Accounts Receivable	The opening and closing balances of the Company’s deferred revenue and accounts receivable are as follows (in thousands): Balance at Beginning of Period (1/1/18) (Decrease) / Increase Balance at End of Period Three Months Ended March 31, 2018 Accounts Receivable $ 86,602 (11,837 ) $ 74,765 Deferred Revenue (Current) $ 197 1,163 $ 1,360 Deferred Revenue (Non-current) $ 254 2,196 $ 2,450
Schedule of Disaggregation of Revenue	Further disaggregation of revenue by geographic country can be found in Note 12. Three Months Ended As a % of March 31, 2018 Total Revenue (dollars in thousands) Americas $ 9,725 13 % EMEA 27,644 38 % APAC 35,572 49 % Total revenue $ 72,941 100 %

FINANCIAL INSTRUMENTS (Tables)

FINANCIAL INSTRUMENTS (Tables)	3 Months Ended
	Mar. 31, 2018
Investments, Debt and Equity Securities [Abstract]
Schedule of Cash, Cash Equivalents and Short- and Long-term Marketable Securities	The following tables set forth the Company’s cash, cash equivalents and short- and long-term marketable securities as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Gross Unrealized Losses Amortized Cost Gains Less than One Year Greater than One Year Estimated Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 52,831 $ — $ — $ — $ 52,831 $ 52,831 $ — Money market funds 8,907 — — — 8,907 8,907 — Repurchase agreements 13,700 — — — 13,700 13,700 — U.S. treasury bonds 31,346 — (99 ) — 31,247 4,999 26,248 Commercial paper 49,141 — (29 ) — 49,112 — 49,112 Certificates of deposit 49,524 6 (107 ) — 49,423 1,700 47,723 Asset-backed securities 40,896 1 (151 ) — 40,746 2,998 37,748 Corporate debt securities 122,100 5 (560 ) (5 ) 121,540 — 121,540 Total $ 368,445 $ 12 $ (946 ) $ (5 ) $ 367,506 $ 85,135 $ 282,371 December 31, 2017 Gross Unrealized Estimated Cash and Cash Marketable Amortized Cost Gains Losses (1) Fair Value Equivalents Securities Cash $ 43,223 $ — $ — $ 43,223 $ 43,223 $ — Money market funds 11,070 — — 11,070 11,070 — Repurchase agreements 12,500 — — 12,500 12,500 — U.S. treasury bonds 26,316 — (80 ) 26,236 — 26,236 Commercial paper 60,623 — (9 ) 60,614 — 60,614 Certificates of deposit 34,993 6 (33 ) 34,966 — 34,966 Asset-backed securities 33,374 1 (53 ) 33,322 702 32,620 Corporate debt securities 142,960 9 (290 ) 142,679 — 142,679 Total $ 365,059 $ 16 $ (465 ) $ 364,610 $ 67,495 $ 297,115 (1) Losses represent marketable securities that were in loss positions for less than one year.
Proceeds from Sales and Maturities of Marketable Securities	The proceeds from the sales and maturities of marketable securities, which were primarily reinvested and resulted in realized gains and losses, were as follows (in thousands): Three Months Ended March 31, 2018 Three Months Ended March 31, 2017 Proceeds from the sales and maturities of marketable securities $ 87,830 $ 38,900 Realized gains $ 4 $ 1 Realized losses $ (2 ) $ —
Contractual Maturities of Short-term and Long-Term Marketable Securities Held	The contractual maturities of short-term and long-term marketable securities held at March 31, 2018 and December 31, 2017 are as follows (in thousands): March 31, 2018 December 31, 2017 Amortized Cost Basis Aggregate Fair Value Amortized Cost Basis Aggregate Fair Value Due within one year $ 223,179 $ 222,540 $ 212,137 $ 211,933 Due after one year through three years 60,131 59,831 85,426 85,182 Total $ 283,310 $ 282,371 $ 297,563 $ 297,115

INVENTORY (Tables)

INVENTORY (Tables)	3 Months Ended
	Mar. 31, 2018
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventory consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Raw materials $ 37,195 $ 32,599 Work-in-process 663 965 Finished goods 19,298 28,668 Inventory $ 57,156 $ 62,232

PROPERTY AND EQUIPMENT (Tables)

PROPERTY AND EQUIPMENT (Tables)	3 Months Ended
	Mar. 31, 2018
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Engineering laboratory equipment $ 42,763 $ 39,433 Computer software 2,565 2,281 Computer equipment 4,636 4,380 Furniture and fixtures 3,201 3,041 Leasehold improvements 3,015 2,282 Construction in progress 5,345 4,591 Total property and equipment 61,525 56,008 Less: Accumulated depreciation (31,099 ) (27,833 ) Property and equipment, net $ 30,426 $ 28,175

ACCRUED LIABILITIES (Tables)

ACCRUED LIABILITIES (Tables)	3 Months Ended
	Mar. 31, 2018
Payables and Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 Employee-related liabilities $ 8,095 $ 5,233 Outsourced foundry services 1,345 95 Goods and services received not invoiced 8,815 12,827 Accrued manufacturing related expenses 7,648 4,007 Warranty reserve 7,418 8,306 Other accrued liabilities 9,461 6,766 Accrued liabilities $ 42,782 $ 37,234

FAIR VALUE MEASUREMENT (Tables)

FAIR VALUE MEASUREMENT (Tables)	3 Months Ended
	Mar. 31, 2018
Fair Value Disclosures [Abstract]
Schedule of Assets Measured at Fair Value on Recurring Basis	The fair value of these assets measured on a recurring basis was determined using the following inputs as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets: Money market funds $ — $ 8,907 $ — $ 8,907 Repurchase agreements — 13,700 — 13,700 U.S. treasury bonds — 31,247 — 31,247 Commercial paper — 49,112 — 49,112 Certificates of deposit — 49,423 — 49,423 Asset-backed securities — 40,746 — 40,746 Corporate debt securities — 121,540 — 121,540 Total $ — $ 314,675 $ — $ 314,675 December 31, 2017 Quoted Prices in Active Markets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) Total Fair Value Assets: Money market funds $ — $ 11,070 $ — $ 11,070 Repurchase agreements — 12,500 — 12,500 U.S. treasury bonds — 26,236 — 26,236 Commercial paper — 60,614 — 60,614 Certificates of deposit — 34,966 — 34,966 Asset-backed securities — 33,322 — 33,322 Corporate debt securities — 142,679 — 142,679 Total $ — $ 321,387 $ — $ 321,387

STOCK COMPENSATION PLANS (Table

STOCK COMPENSATION PLANS (Tables)	3 Months Ended
	Mar. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Classification of Stock-based Compensation	The following table summarizes the classification of stock-based compensation in the condensed consolidated statements of operations for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Cost of revenue $ 521 $ 442 Research and development 3,788 2,992 Sales, general and administrative 2,229 1,198 Total stock-based compensation $ 6,538 $ 4,632
Schedule of Stock-Based Compensation Expense by Award Type	The following table summarizes stock-based compensation expense by award type for the three months ended March 31, 2018 and 2017 (in thousands): Three Months Ended March 31, 2018 2017 Stock options $ 601 $ 666 Restricted stock units 5,595 3,686 Employee stock purchase plan 298 251 Other awards 44 29 Total stock-based compensation $ 6,538 $ 4,632
Stock Option Activity	A summary of stock option activity under the Company’s equity incentive plans for the three months ended March 31, 2018 is as follows: Number of Options (in thousands) Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (in years) Aggregate Intrinsic Value (in thousands) Outstanding at December 31, 2017 1,634 $ 8.34 6.6 $ 47,356 Granted — $ — Exercised (220 ) $ 4.40 $ 7,660 Cancelled (25 ) $ 11.95 Outstanding at March 31, 2018 1,389 $ 8.90 6.4 $ 42,655 Vested at: March 31, 2018 1,389 $ 8.90 6.4 $ 42,655 December 31, 2017 1,634 $ 8.34 6.6 $ 47,356 Exercisable at: March 31, 2018 808 $ 5.91 5.8 $ 26,919 December 31, 2017 907 $ 5.28 5.9 $ 28,634
Weighted-Average Assumptions Used to Estimate Fair Value	The Company estimated the fair value of the PRSUs using a Monte Carlo valuation model on the date of grant, using the following assumptions: Risk-free interest rate 2.3% Expected dividend yield None Expected volatility 51.4% Expected term (in years) 2.9 Grant date fair value of underlying shares $39.02
Summary of Changes in Company's RSU	A summary of the changes in the Company’s RSUs during the three months ended March 31, 2018 is as follows: RSUs (in thousands) Weighted-Average Grant Date Fair Value Outstanding at December 31, 2017 2,288 $ 36.08 Granted 588 $ 43.20 Vested (214 ) $ 34.69 Cancelled (11 ) $ 25.92 Outstanding at March 31, 2018 2,651 $ 37.81

NET (LOSS) INCOME PER SHARE (Ta

NET (LOSS) INCOME PER SHARE (Tables)	3 Months Ended
	Mar. 31, 2018
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net (Loss) Income Per Share	The following table sets forth the computation of the Company’s basic and diluted net (loss) income per share (in thousands, except per share amounts): Three Months Ended March 31, 2018 2017 Numerator: Net (loss) income $ (9,078 ) $ 35,709 Denominator: Weighted-average shares used to compute net (loss) income per share - basic 39,836 38,308 Dilutive effect of stock options, unvested restricted stock and restricted stock units and employee stock purchase plan — 3,346 Weighted-average shares used to compute net (loss) income per share - diluted 39,836 41,654 Net (loss) income per share Basic $ (0.23 ) $ 0.93 Diluted $ (0.23 ) $ 0.86
Summary of Common Stock Equivalents Excluded from Computation of Diluted Net Income (Loss) Per Share	The following common stock equivalents (in thousands) were excluded from the computation of diluted net (loss) income per share for the periods presented because including them would have been antidilutive: Three Months Ended March 31, 2018 2017 Options to purchase common stock 1,218 49 Unvested restricted stock units and awards 1,445 152 Employee stock purchase plan 3 —

COMMITMENTS AND CONTINGENCIES (

COMMITMENTS AND CONTINGENCIES (Tables)	3 Months Ended
	Mar. 31, 2018
Commitments and Contingencies Disclosure [Abstract]
Future Annual Minimum Lease Payments	Future minimum lease payments due under these non-cancelable lease agreements as of March 31, 2018 , are as follows (in thousands): Amounts Remaining 2018 $ 2,481 2019 3,311 2020 3,339 2021 3,235 2022 2,415 Thereafter 5,393 Total $ 20,174
Schedule of Changes in Product Warrant Liability	Changes in the Company’s warranty liability, which is included as a component of accrued liabilities on the condensed consolidated balance sheets, are set forth in the table below (in thousands): Three Months Ended March 31, 2018 2017 Warranty reserve, beginning of period $ 8,306 $ 2,158 Provisions made to warranty reserve during the period 3,463 1,138 Charges against warranty reserve during the period (4,351 ) (1,183 ) Warranty reserve, end of period $ 7,418 $ 2,113

SEGMENT INFORMATION AND GEOGR36

SEGMENT INFORMATION AND GEOGRAPHIC DATA (Tables)	3 Months Ended
	Mar. 31, 2018
Segment Reporting [Abstract]
Summary of Revenue by Geographic Region	Revenue by geographic region, based on ship-to destinations, which in certain instances may be the location of a contract manufacturer rather than the Company’s end customer, was as follows (in thousands): Three Months Ended March 31, 2018 2017 United States $ 9,427 $ 12,414 China 22,083 56,982 Germany 19,746 12,966 Thailand 7,119 11,604 Other 14,566 20,701 Total revenue $ 72,941 $ 114,667
Summary of Total Long-Lived Assets by Geographic Region	Total long-lived assets by geographic region consisted of the following as of March 31, 2018 and December 31, 2017 (in thousands): March 31, 2018 December 31, 2017 United States $ 20,866 $ 19,065 China 1,204 1,165 Thailand 6,271 7,065 Other 2,085 880 Total long-lived assets $ 30,426 $ 28,175

CONCENTRATIONS OF RISK (Tables)

CONCENTRATIONS OF RISK (Tables)	3 Months Ended
	Mar. 31, 2018
Customer Concentration Risk
Concentration Risk [Line Items]
Summary of Concentrations of Risk	Customers with revenue equal to or greater than 10% of total revenue for the three months ended March 31, 2018 and 2017 were as follows: Three Months Ended March 31, 2018 2017 A (1) 20 % 41 % B 17 % 11 % C 20 % * * Less than 10% of revenue in the period indicated (1) Customer A is currently subject to U.S. Department of Commerce restrictions that prevent sales to this customer after April 15, 2018. Refer to Note 16 for additional information. Customers that accounted for equal to or greater than 10% of accounts receivable at March 31, 2018 and December 31, 2017 were as follows: March 31, 2018 December 31, 2017 A (1) 24 % 15 % B * 10 % C 21 % 19 % * Less than 10% of accounts receivable at the date indicated (1) Customer A is currently subject to U.S. Department of Commerce restrictions that prevent sales to this customer after April 15, 2018. To date, the Company has concluded that Customer A’s receivable balances as of March 31, 2018 are collectible. The Company will continue to evaluate collectibility of Customer A’s receivable balances. Refer to Note 16 for additional information.
Supplier Concentration Risk
Concentration Risk [Line Items]
Summary of Concentrations of Risk	For the three months ended March 31, 2018 and 2017 , total purchases from each of the suppliers were as follows: Three Months Ended March 31, 2018 2017 W * 40 % X 22 % * Y 48 % 41 % Z * 10 % * Less than 10% of total purchases in the period indicated

NATURE OF THE BUSINESS AND OP38

NATURE OF THE BUSINESS AND OPERATIONS (Details)	3 Months Ended
	Mar. 31, 2018GBTB
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Optical interconnect modules transmission speed | TB	1.2
Minimum
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Optical interconnect modules transmission speed	100
Maximum
Organization Consolidation and Presentation of Financial Statements Disclosure [Line Items]
Optical interconnect modules transmission speed	400

BASIS OF PRESENTATION AND SUM39

BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prepaid expenses and other current assets	$ 19,481		$ 18,985
Increase in prepaid expenses and other current assets	$ 665	$ 5,435
Reclassifications
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Prepaid expenses and other current assets			200
Deferred product costs			$ (200)
Increase in prepaid expenses and other current assets		200
Increase in deferred product costs		$ (200)

REVENUE - Narrative (Details)

REVENUE - Narrative (Details)	3 Months Ended
	Mar. 31, 2018USD ($)
Disaggregation Of Revenue [Line Items]
Capitalized contracts	$ 0
Minimum
Disaggregation Of Revenue [Line Items]
Standard warranty period	12 months
Payment terms on invoiced amounts	30 days
Maximum
Disaggregation Of Revenue [Line Items]
Standard warranty period	24 months
Payment terms on invoiced amounts	60 days

REVENUE - Deferred Revenue and

REVENUE - Deferred Revenue and Accounts Receivable (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018	Dec. 31, 2017
Revenue from Contract with Customer [Abstract]
Deferred Revenue (Current)	$ 1,360		$ 197
Deferred Revenue (Non-current)	2,450		254
Accounts receivable	74,765		$ 86,602	$ 86,602
Increase / (Decrease), Deferred Revenue (Current)	1,163
Deferred revenue	1,360			$ 573
Increase / (Decrease), Deferred Revenue (Non-current)	2,196
Increase / (Decrease), Accounts Receivable	$ (11,837)	$ 6,764

REVENUE - Disaggregation of Rev

REVENUE - Disaggregation of Revenue (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018USD ($)
Disaggregation Of Revenue [Line Items]
Revenue	$ 72,941
Revenue, as a % of Total Revenue	100.00%
Americas
Disaggregation Of Revenue [Line Items]
Revenue	$ 9,725
Revenue, as a % of Total Revenue	13.00%
EMEA
Disaggregation Of Revenue [Line Items]
Revenue	$ 27,644
Revenue, as a % of Total Revenue	38.00%
APAC
Disaggregation Of Revenue [Line Items]
Revenue	$ 35,572
Revenue, as a % of Total Revenue	49.00%

FINANCIAL INSTRUMENTS - Schedul

FINANCIAL INSTRUMENTS - Schedule of Cash, Cash Equivalents and Short- and Long-term Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	$ 368,445	$ 365,059
Gross Unrealized Gains	12	16
Gross Unrealized Losses, Less than One Year	(946)
Gross Unrealized Losses, Greater than One Year	(5)
Gross Unrealized Losses		(465)
Estimated Fair Value	367,506	364,610
Cash and Cash Equivalents	85,135	67,495
Marketable Securities	282,371	297,115
Corporate debt securities
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	122,100	142,960
Gross Unrealized Gains	5	9
Gross Unrealized Losses, Less than One Year	(560)
Gross Unrealized Losses, Greater than One Year	(5)
Gross Unrealized Losses		(290)
Estimated Fair Value	121,540	142,679
Cash and Cash Equivalents	0	0
Marketable Securities	121,540	142,679
Cash
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	52,831	43,223
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than One Year	0
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		0
Estimated Fair Value	52,831	43,223
Cash and Cash Equivalents	52,831	43,223
Marketable Securities	0	0
Money market funds
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	8,907	11,070
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than One Year	0
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		0
Estimated Fair Value	8,907	11,070
Cash and Cash Equivalents	8,907	11,070
Marketable Securities	0	0
Repurchase agreements
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	13,700	12,500
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than One Year	0
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		0
Estimated Fair Value	13,700	12,500
Cash and Cash Equivalents	13,700	12,500
Marketable Securities	0	0
U.S. treasury bonds
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	31,346	26,316
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than One Year	(99)
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		(80)
Estimated Fair Value	31,247	26,236
Cash and Cash Equivalents	4,999	0
Marketable Securities	26,248	26,236
Commercial paper
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	49,141	60,623
Gross Unrealized Gains	0	0
Gross Unrealized Losses, Less than One Year	(29)
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		(9)
Estimated Fair Value	49,112	60,614
Cash and Cash Equivalents	0	0
Marketable Securities	49,112	60,614
Certificates of deposit
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	49,524	34,993
Gross Unrealized Gains	6	6
Gross Unrealized Losses, Less than One Year	(107)
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		(33)
Estimated Fair Value	49,423	34,966
Cash and Cash Equivalents	1,700	0
Marketable Securities	47,723	34,966
Asset-backed securities
Schedule Of Cash Cash Equivalents And Marketable Securities [Line Items]
Amortized Cost	40,896	33,374
Gross Unrealized Gains	1	1
Gross Unrealized Losses, Less than One Year	(151)
Gross Unrealized Losses, Greater than One Year	0
Gross Unrealized Losses		(53)
Estimated Fair Value	40,746	33,322
Cash and Cash Equivalents	2,998	702
Marketable Securities	$ 37,748	$ 32,620

FINANCIAL INSTRUMENTS - Proceed

FINANCIAL INSTRUMENTS - Proceeds from Sales and Maturities of Marketable Securities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Proceeds from the sales and maturities of marketable securities	$ 87,830	$ 38,900
Realized gains	4	1
Realized losses	$ (2)	$ 0

FINANCIAL INSTRUMENTS - Contrac

FINANCIAL INSTRUMENTS - Contractual Maturities of Short-term and Long-term Marketable Securities Held (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Due within one year, Amortized Cost Basis	$ 223,179	$ 212,137
Due within one year, Aggregate Fair Value	222,540	211,933
Due after one year through three years, Amortized Cost Basis	60,131	85,426
Due after one year through three years, Aggregate Fair Value	59,831	85,182
Amortized Cost Basis	283,310	297,563
Aggregate Fair Value	$ 282,371	$ 297,115

INVENTORY - Schedule of Invento

INVENTORY - Schedule of Inventory (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Inventory Disclosure [Abstract]
Raw materials	$ 37,195	$ 32,599
Work-in-process	663	965
Finished goods	19,298	28,668
Inventory	57,156	$ 62,232
Inventory write-offs	$ 3,900

PROPERTY AND EQUIPMENT - Schedu

PROPERTY AND EQUIPMENT - Schedule of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 61,525	$ 56,008
Less: Accumulated depreciation	(31,099)	(27,833)
Property and equipment, net	30,426	28,175
Engineering laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	42,763	39,433
Computer software
Property, Plant and Equipment [Line Items]
Total property and equipment	2,565	2,281
Computer equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	4,636	4,380
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	3,201	3,041
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	3,015	2,282
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 5,345	$ 4,591

PROPERTY AND EQUIPMENT - Narrat

PROPERTY AND EQUIPMENT - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 3,266	$ 2,877

ACCRUED LIABILITIES - Schedule

ACCRUED LIABILITIES - Schedule of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Employee-related liabilities	$ 8,095	$ 5,233
Outsourced foundry services	1,345	95
Goods and services received not invoiced	8,815	12,827
Accrued manufacturing related expenses	7,648	4,007
Warranty reserve	7,418	8,306	$ 2,113	$ 2,158
Other accrued liabilities	9,461	6,766
Accrued liabilities	42,782	37,234
Reclassifications
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Other accrued liabilities		400
Accrued income taxes		$ 400
ZTE Kangxun Telecom Co. Ltd
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Accrued manufacturing related expenses	$ 3,200

FAIR VALUE MEASUREMENT - Summar

FAIR VALUE MEASUREMENT - Summary of Assets And Liabilities Measured at Fair Value on Recurring Basis (Details) - Recurring Basis - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 314,675	$ 321,387
Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	314,675	321,387
Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Repurchase agreements
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	13,700	12,500
Repurchase agreements | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Repurchase agreements | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	13,700	12,500
Repurchase agreements | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
U.S. treasury bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	31,247	26,236
U.S. treasury bonds | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
U.S. treasury bonds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	31,247	26,236
U.S. treasury bonds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	49,112	60,614
Commercial paper | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Commercial paper | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	49,112	60,614
Commercial paper | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Certificates of deposit
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	49,423	34,966
Certificates of deposit | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Certificates of deposit | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	49,423	34,966
Certificates of deposit | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Asset-backed securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	40,746	33,322
Asset-backed securities | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Asset-backed securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	40,746	33,322
Asset-backed securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	121,540	142,679
Corporate debt securities | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Corporate debt securities | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	121,540	142,679
Corporate debt securities | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Money market funds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	8,907	11,070
Money market funds | Quoted Prices in Active Markets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	0	0
Money market funds | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	8,907	11,070
Money market funds | Significant Unobservable Inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 0	$ 0

FAIR VALUE MEASUREMENT - Narrat

FAIR VALUE MEASUREMENT - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Transfers between fair value measurement levels	$ 0	$ 0

STOCK COMPENSATION PLANS - Clas

STOCK COMPENSATION PLANS - Classification of Stock-based Compensation (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 6,538	$ 4,632
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	521	442
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	3,788	2,992
Sales, general and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 2,229	$ 1,198

STOCK COMPENSATION PLANS - Sche

STOCK COMPENSATION PLANS - Schedule of Stock-Based Compensation Expense by Award Type (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 6,538	$ 4,632
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	298	251
Stock options
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	601	666
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	5,595	3,686
Other awards
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 44	$ 29

STOCK COMPENSATION PLANS - Stoc

STOCK COMPENSATION PLANS - Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Number of Options, Abstract
Number of options outstanding at beginning of period (in shares)	1,634
Number of options granted (in shares)	0
Number of options exercised (in shares)	(220)
Number of options cancelled (in shares)	(25)
Number of options outstanding at end of period (in shares)	1,389	1,634
Number of options vested and expected to vest (in shares)	1,389	1,634
Number of options exercisable (in shares)	808	907
Weighted-Average Exercise Price, Abstract
Weighted-average exercise price outstanding at beginning of period (in USD per share)	$ 8.34
Options granted, Weighted-average exercise price (in USD per share)	0
Options exercised, Weighted-average exercise price (in USD per share)	4.40
Options cancelled, Weighted-average exercise price (in USD per share)	11.95
Weighted-average exercise price outstanding at end of period (in USD per share)	8.90	$ 8.34
Options vested and expected to vest, Weighted-average exercise price (in USD per share)	8.90	8.34
Options exercisable, Weighted-average exercise price (in USD per share)	$ 5.91	$ 5.28
Weighted-Average Remaining Contract Term, Abstract
Options outstanding, Weighted-average remaining contractual term (in years)	6 years 4 months 24 days	6 years 7 months 6 days
Options vested and expected to vest, Weighted-average remaining contractual term (in years)	6 years 4 months 24 days	6 years 7 months 6 days
Options exercisable, Weighted-average remaining contractual term (in years)	5 years 9 months 18 days	5 years 10 months 24 days
Aggregate Intrinsic Value, Abstract
Options outstanding, Aggregate intrinsic value at beginning of period	$ 47,356
Options exercised, Aggregate intrinsic value	7,660
Options outstanding, Aggregate intrinsic value at end of period	42,655	$ 47,356
Options vested and expected to vest, Aggregate intrinsic value	42,655	47,356
Options exercisable, Aggregate intrinsic value	$ 26,919	$ 28,634

STOCK COMPENSATION PLANS - Narr

STOCK COMPENSATION PLANS - Narrative (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 28, 2018	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of options granted (in shares)		0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total unrecognized compensation cost, stock options		$ 4,100,000		$ 4,800,000
Weighted average recognition period		1 year 10 months 24 days		2 years 2 months 12 days
Number of options granted (in shares)		0	0
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average recognition period		3 years 1 month 6 days		2 years 10 months 24 days
Restricted stock units granted (in shares)		588,000
Vested awards settled in cash		$ 0
Unrecognized stock-based compensation expense		$ 64,800,000		$ 47,800,000
Restricted stock units | Employees and Executives | 2016 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted (in shares)		497,000
Awards vesting period		4 years
Performance-Based RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Right to receive number of common stock upon achievement of vesting conditions		1
Performance-Based RSUs | Executive
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted (in shares)	90,808	90,808
Performance-Based RSUs | Executive | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units granted (in shares)		90,808
Earned PRSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance objective period		3 years

STOCK COMPENSATION PLANS - Weig

STOCK COMPENSATION PLANS - Weighted-Average Assumptions Used to Estimate Fair Value (Details) - Performance-Based RSUs	3 Months Ended
	Mar. 31, 2018$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.30%
Expected dividend yield	0.00%
Expected volatility	51.40%
Expected term (in years)	2 years 10 months 24 days
Grant date fair value of underlying shares (in USD per share)	$ 39.02

STOCK COMPENSATION PLANS - Chan

STOCK COMPENSATION PLANS - Changes in Company Restricted Stock Units (Details) - Restricted stock units shares in Thousands	3 Months Ended
	Mar. 31, 2018$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Shares outstanding at beginning of period (in shares) | shares	2,288
Granted (in shares) | shares	588
Vested (in shares) | shares	(214)
Cancelled (in shares) | shares	(11)
Shares outstanding at end of period (in shares) | shares	2,651
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Shares outstanding, Weighted-average grant date fair value at beginning of period (in USD per share) | $ / shares	$ 36.08
Granted, Weighted-average grant date fair value (in USD per share) | $ / shares	43.20
Vested, Weighted-average grant date fair value (in USD per share) | $ / shares	34.69
Cancelled, Weighted-average grant date fair value (in USD per share) | $ / shares	25.92
Shares outstanding, Weighted-average grant date fair value at end of period (in USD per share) | $ / shares	$ 37.81

NET (LOSS) INCOME PER SHARE - C

NET (LOSS) INCOME PER SHARE - Computation of Basic and Diluted Net Income Per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Numerator:
Net (loss) income	$ (9,078)	$ 35,709
Denominator:
Weighted-average shares used to compute net (loss) income per share - basic (in shares)	39,836	38,308
Dilutive effect of stock options, unvested restricted stock and restricted stock units and employee stock purchase plan (in shares)	0	3,346
Weighted-average shares used to compute net (loss) income per share - diluted (in shares)	39,836	41,654
Net (loss) income per share
Basic (in USD per share)	$ (0.23)	$ 0.93
Diluted (in USD per share)	$ (0.23)	$ 0.86

NET (LOSS) INCOME PER SHARE - S

NET (LOSS) INCOME PER SHARE - Summary of Common Stock Equivalents Excluded from Computation of Diluted Net Income Per Share (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Options to purchase common stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share (in shares)	1,218	49
Unvested restricted stock units and awards
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share (in shares)	1,445	152
Employee stock purchase plan
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share (in shares)	3	0

NET (LOSS) INCOME PER SHARE - N

NET (LOSS) INCOME PER SHARE - Narrative (Details) - shares	1 Months Ended	3 Months Ended
	Feb. 28, 2018	Mar. 31, 2018
Performance-Based RSUs | Executive
Earnings Per Share [Line Items]
Restricted stock units granted (in shares)	90,808	90,808

COMMITMENTS AND CONTINGENCIES -

COMMITMENTS AND CONTINGENCIES - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended
	May 31, 2017contract_manufacturerAC400_UnitCFP_Unit	Mar. 31, 2018USD ($)	Mar. 31, 2017USD ($)
Loss Contingencies [Line Items]
Operating leases rent expense | $		$ 1.2	$ 1.5
Minimum
Loss Contingencies [Line Items]
Standard warranty period on repair or replacement of defective products		12 months
Maximum
Loss Contingencies [Line Items]
Standard warranty period on repair or replacement of defective products		24 months
Contract manufacturer quality issue
Loss Contingencies [Line Items]
Number of contract manufacturers with quality issue	1
Number of contract manufacturers	3
Contract manufacturer quality issue | AC400 Unit
Loss Contingencies [Line Items]
Defective units | AC400_Unit	1,300
Contract manufacturer quality issue | CFP Unit
Loss Contingencies [Line Items]
Defective units | CFP_Unit	5,100

COMMITMENTS AND CONTINGENCIES62

COMMITMENTS AND CONTINGENCIES - Future Annual Minimum Lease Payments (Details) $ in Thousands	Mar. 31, 2018USD ($)
Commitments and Contingencies Disclosure [Abstract]
Remaining 2,018	$ 2,481
2,019	3,311
2,020	3,339
2,021	3,235
2,022	2,415
Thereafter	5,393
Total	$ 20,174

COMMITMENTS AND CONTINGENCIES63

COMMITMENTS AND CONTINGENCIES - Schedule of Changes in Product Warrant Liability (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Commitments and Contingencies Disclosure [Abstract]
Warranty reserve, beginning of period	$ 8,306	$ 2,158
Provisions made to warranty reserve during the period	3,463	1,138
Charges against warranty reserve during the period	(4,351)	(1,183)
Warranty reserve, end of period	$ 7,418	$ 2,113

INCOME TAXES - Narrative (Detai

INCOME TAXES - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Provisional income tax expense under SAB 118			$ 31,400
Benefit from income taxes	$ 4,301	$ 5,421
Effective income tax rate	32.10%	(17.90%)
Uncertain tax positions	$ 4,800		4,500
Unrecognized tax benefits that, if recognized, would favorably impact effective tax rate	$ 2,400		$ 2,300

SEGMENT INFORMATION AND GEOGR65

SEGMENT INFORMATION AND GEOGRAPHIC DATA - Narrative (Details)	3 Months Ended
	Mar. 31, 2018segment
Segment Reporting [Abstract]
Number of operating segments	1

SEGMENT INFORMATION AND GEOGR66

SEGMENT INFORMATION AND GEOGRAPHIC DATA - Summary of Revenue by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Revenue	$ 72,941	$ 114,667
United States
Segment Reporting Information [Line Items]
Revenue	9,427	12,414
China
Segment Reporting Information [Line Items]
Revenue	22,083	56,982
Germany
Segment Reporting Information [Line Items]
Revenue	19,746	12,966
Thailand
Segment Reporting Information [Line Items]
Revenue	7,119	11,604
Other
Segment Reporting Information [Line Items]
Revenue	$ 14,566	$ 20,701

SEGMENT INFORMATION AND GEOGR67

SEGMENT INFORMATION AND GEOGRAPHIC DATA - Summary of Total Long-Lived Assets by Geographic Region (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Property and equipment, net	$ 30,426	$ 28,175
United States
Segment Reporting Information [Line Items]
Property and equipment, net	20,866	19,065
China
Segment Reporting Information [Line Items]
Property and equipment, net	1,204	1,165
Thailand
Segment Reporting Information [Line Items]
Property and equipment, net	6,271	7,065
Other
Segment Reporting Information [Line Items]
Property and equipment, net	$ 2,085	$ 880

CONCENTRATIONS OF RISK - Summar

CONCENTRATIONS OF RISK - Summary of Customer Concentration of Total Revenue (Details) - Customer Concentration Risk - Revenue	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	20.00%	41.00%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage	17.00%	11.00%
Customer C
Concentration Risk [Line Items]
Concentration risk, percentage	20.00%

CONCENTRATIONS OF RISK - Summ69

CONCENTRATIONS OF RISK - Summary of Customer Concentration of Accounts Receivable (Details) - Customer Concentration Risk - Accounts Receivable	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Customer A
Concentration Risk [Line Items]
Concentration risk, percentage	24.00%	15.00%
Customer B
Concentration Risk [Line Items]
Concentration risk, percentage		10.00%
Customer C
Concentration Risk [Line Items]
Concentration risk, percentage	21.00%	19.00%

CONCENTRATIONS OF RISK - Summ70

CONCENTRATIONS OF RISK - Summary of Supplier Concentration (Details) - Supplier Concentration Risk - Purchases	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Supplier W
Concentration Risk [Line Items]
Concentration risk, percentage	40.00%
Supplier X
Concentration Risk [Line Items]
Concentration risk, percentage	22.00%
Supplier Y
Concentration Risk [Line Items]
Concentration risk, percentage	48.00%	41.00%
Supplier Z
Concentration Risk [Line Items]
Concentration risk, percentage		10.00%

CONCENTRATIONS OF RISK - Narrat

CONCENTRATIONS OF RISK - Narrative (Details)	3 Months Ended
	Mar. 31, 2018
Vendor A | Supplier Concentration Risk | Research and development
Concentration Risk [Line Items]
Concentration risk, percentage	12.00%

RELATED PARTIES - Narrative (De

RELATED PARTIES - Narrative (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 22, 2018	Mar. 31, 2018	Mar. 31, 2017
ADI
Related Party Transaction [Line Items]
Purchase from related party		$ 0.7	$ 1.2
Product development agreement	$ 2
Product development agreement costs incurred		0.5
M/A-COM
Related Party Transaction [Line Items]
Purchase from related party		$ 0.3

SUBSEQUENT EVENTS (Details)

SUBSEQUENT EVENTS (Details) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Apr. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Subsequent Event [Line Items]
Inventory write-off and increase in reserves	$ 7,100,000
Accounts receivable	74,765,000			$ 86,602,000	$ 86,602,000
Subsequent Event
Subsequent Event [Line Items]
Authorized stock repurchase amount			$ 60,000,000
ZTE
Subsequent Event [Line Items]
Accounts receivable	$ 17,600,000
Revenue | Customer Concentration Risk | ZTE
Subsequent Event [Line Items]
Concentration risk, percentage	20.00%	41.00%