Neophotonics (NPTN) 10-Q 7 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	Apr. 30, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	NPTN
Entity Registrant Name	NEOPHOTONICS CORP
Entity Central Index Key	0001227025
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		46,474,327

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 59,793	$ 58,185
Short-term investments	7,524	7,481
Restricted cash	11,577	11,053
Accounts receivable, net of allowance for doubtful accounts	65,210	74,751
Inventories	53,618	52,159
Assets held for sale	3,074	2,971
Prepaid expenses and other current assets	23,995	26,605
Total current assets	224,791	233,205
Property, plant and equipment, net	95,688	100,090
Operating lease right-of-use assets	16,847
Purchased intangible assets, net	2,736	3,018
Goodwill	1,115	1,115
Other long-term assets	3,159	3,148
Total assets	344,336	340,576
Current liabilities:
Accounts payable	57,853	58,403
Notes payable and short-term borrowing	2,339	4,795
Current portion of long-term debt	2,963	2,897
Accrued and other current liabilities	50,269	50,288
Total current liabilities	113,424	116,383
Long-term debt, net of current portion	50,213	50,454
Operating lease liabilities, noncurrent	18,019
Other noncurrent liabilities	10,122	13,499
Total liabilities	191,778	180,336
Commitments and contingencies (Note 12)
Stockholders’ equity:
Preferred stock, $0.0025 par value, 10,000 shares authorized, no shares issued or outstanding	0	0
Common stock, $0.0025 par value, 100,000 shares authorized; As of March 31, 2019, 46,455 shares issued and outstanding; as of December 31, 2018, 46,378 shares issued and outstanding	116	116
Additional paid-in capital	568,194	564,722
Accumulated other comprehensive loss	(4,189)	(7,126)
Accumulated deficit	(411,563)	(397,472)
Total stockholders’ equity	152,558	160,240
Total liabilities and stockholders’ equity	$ 344,336	$ 340,576

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) (Unaudited) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.0025	$ 0.0025
Preferred stock, shares authorized (in shares)	10,000,000	10,000,000
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0025	$ 0.0025
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	46,455,000	46,378,000
Common stock, shares outstanding (in shares)	46,455,000	46,378,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Revenue	$ 79,366	$ 68,586
Cost of goods sold	63,629	59,404
Gross profit	15,737	9,182
Operating expenses:
Research and development	14,683	13,888
Sales and marketing	4,603	4,124
General and administrative	7,753	7,650
Amortization of purchased intangible assets	119	119
Asset sale related costs	329	14
Restructuring charges	179	31
Total operating expenses	27,666	25,826
Loss from operations	(11,929)	(16,644)
Interest income	99	93
Interest expense	(493)	(708)
Other income (expense), net	(1,598)	(349)
Total interest and other income (expense), net	(1,992)	(964)
Loss before income taxes	(13,921)	(17,608)
Provision for income taxes	(170)	(638)
Net loss	$ (14,091)	$ (18,246)
Basic net loss per share (USD per share)	$ (0.30)	$ (0.41)
Diluted net loss per share (USD per share)	$ (0.30)	$ (0.41)
Weighted average shares used to compute basic net loss per share (in shares)	46,414	44,259
Weighted average shares used to compute diluted net loss per share (in shares)	46,414	44,259

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Statement of Comprehensive Income [Abstract]
Net loss	$ (14,091)	$ (18,246)
Other comprehensive income:
Foreign currency translation adjustments, net of zero tax	2,937	6,102
Unrealized gains on available-for-sale securities, net of zero tax	0	1
Total other comprehensive income	2,937	6,103
Comprehensive loss	$ (11,154)	$ (12,143)

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common stock	Additional paid-in capital	Accumulated other comprehensive income (loss)	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2017		44,219
Beginning balance at Dec. 31, 2017	$ 194,451	$ 111	$ 545,953	$ 398	$ (352,011)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(12,143)			6,103	(18,246)
Issuance of common stock upon exercise of stock options (in shares)		40
Issuance of common stock upon exercise of stock options	142	$ 0	142
Issuance of common stock under employee stock purchase plan (in shares)		0
Issuance of common stock under employee stock purchase plan	0	$ 0	0
Issuance of common stock for vested restricted stock units (in shares)		64
Issuance of common stock for vested restricted stock units	0	$ 0	0
Tax withholding related to vesting of restricted stock units (in shares)		(9)
Tax withholding related to vesting of restricted stock units	(60)		(60)
Stock-based compensation costs	3,154		3,154
Ending Balance (in shares) at Mar. 31, 2018		44,314
Ending balance at Mar. 31, 2018	183,720	$ 111	549,189	6,501	(372,081)
Beginning balance (in shares) at Dec. 31, 2018		46,378
Beginning balance at Dec. 31, 2018	160,240	$ 116	564,722	(7,126)	(397,472)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive income (loss)	(11,154)			2,937	(14,091)
Issuance of common stock upon exercise of stock options (in shares)		48
Issuance of common stock upon exercise of stock options	166		166
Issuance of common stock under employee stock purchase plan (in shares)		0
Issuance of common stock under employee stock purchase plan	0	$ 0	0
Issuance of common stock for vested restricted stock units (in shares)		42
Issuance of common stock for vested restricted stock units	0
Tax withholding related to vesting of restricted stock units (in shares)		(13)
Tax withholding related to vesting of restricted stock units	(82)		(82)
Stock-based compensation costs	3,388		3,388
Ending Balance (in shares) at Mar. 31, 2019		46,455
Ending balance at Mar. 31, 2019	$ 152,558	$ 116	$ 568,194	$ (4,189)	$ (411,563)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (14,091)	$ (18,246)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	8,851	8,005
Stock-based compensation expense	3,338	3,347
Deferred taxes	0	(42)
Others	109	116
Loss on sale of assets and other write-offs	85	2
Loss (gain) on foreign currency hedges	0	(1,557)
Allowance for doubtful accounts	0	(385)
Write-down of inventories	764	1,795
Amortization of operating lease right-of-use assets	432	0
Foreign currency remeasurement	1,818	2,299
Change in assets and liabilities, net of effects of asset sale:
Accounts receivable	9,675	(383)
Inventories	(1,654)	(1,744)
Prepaid expenses and other assets	2,804	5,107
Accounts payable	(1,232)	(2,208)
Accrued and other liabilities	(2,200)	438
Net cash provided by (used in) operating activities	8,699	(3,456)
Cash flows from investing activities
Purchase of property, plant and equipment	(3,600)	(8,293)
Proceeds from sale of property, plant and equipment and other assets	4	9
Purchase of marketable securities	(43)	(37)
Settlement of foreign currency hedges	0	1,566
Net cash used in investing activities	(3,639)	(6,755)
Cash flows from financing activities
Proceeds from exercise of stock options and issuance of stock under ESPP	157	124
Tax withholding on restricted stock units	(82)	(60)
Proceeds from bank loans, net of debt issuance costs	5,000	24,442
Repayment of bank loans	(5,764)	(21,844)
Proceeds from issuance of notes payable	0	698
Repayment of notes payable	(2,559)	(868)
Repayment of finance lease liabilities	(33)	0
Proceeds from government grants	0	472
Net cash (used in) provided by financing activities	(3,281)	2,964
Effect of exchange rates on cash, cash equivalents and restricted cash	353	272
Net increase (decrease) in cash, cash equivalents and restricted cash	2,132	(6,975)
Cash, cash equivalents and restricted cash at the beginning of the period	69,238	81,564
Cash, cash equivalents and restricted cash at the end of the period	71,370	74,589
Supplemental disclosure of non-cash investing and financing activities:
Decrease (increase) in unpaid property, plant and equipment	$ (257)	$ 6,447

Basis of presentation and signi

Basis of presentation and significant accounting policies	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of presentation and significant accounting policies	Basis of presentation and significant accounting policies Basis of Presentation and Consolidation The condensed consolidated financial statements of NeoPhotonics Corporation (“NeoPhotonics” or the “Company”) as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 , have been prepared in accordance with the instructions on Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). In accordance with those rules and regulations, the Company has omitted certain information and notes normally provided in the Company’s annual consolidated financial statements. In the opinion of management, the condensed consolidated financial statements contain all adjustments, consisting only of normal recurring items, except as otherwise noted, necessary for the fair presentation of the Company’s financial position and results of operations for the interim periods. The year-end condensed consolidated balance sheet data was derived from audited consolidated financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles (“U.S. GAAP”). These condensed consolidated financial statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 . The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results expected for the entire fiscal year. All intercompany accounts and transactions have been eliminated. Going Concern Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern , requires an entity to disclose information about its potential inability to continue as a going concern when conditions and events indicate that it is probable that the entity may be unable to meet its obligations as they become due within one year. Management has assessed the Company’s ability to continue as a going concern within one year of the filing date of this Quarterly Report on Form 10-Q with the SEC in May 2019. The accompanying unaudited condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business. As of March 31, 2019 , the Company’s working capital was $111.4 million , including available cash, cash equivalents, short-term investments and restricted cash of approximately $78.9 million . In the first three months of 2019, the Company had operating losses of $11.9 million and net cash provided by operations of $8.7 million . The Company had an accumulated deficit of approximately $411.6 million as of March 31, 2019 . Through 2017 and the early part of 2018, the Company's operating results and cash flows were negatively affected by demand that was lower than customer estimates that were used to put capacity in place in 2016 and 2017. In the second half of 2018, demand continued to strengthen, primarily due to volume growth in the Americas as a result of metro and, particularly, data center interconnect deployments, as well as being the result of increased domestic provincial deployments in China plus exports by Chinese OEMs for international deployments. To adjust to the demand that was less than estimates used for capacity decisions, the Company implemented restructuring plans in May and September 2017 that included a reduction in force and consolidation of facilities, in order to reduce expenses. The Company has also reduced or delayed certain product development projects and capital expenditures, aggressively pursued collections of accounts and notes receivable and continued to closely manage production and inventory levels. The Company continues to implement actions to improve cash flow and profitability. In September 2017, the Company entered into a revolving line of credit agreement with Wells Fargo Bank, National Association ("Wells Fargo") which provides for borrowings under an accounts receivable based formula up to a maximum of $50.0 million . As of March 31, 2019, $36.3 million was outstanding under this line. The remaining borrowing capacity as of March 31, 2019 was $13.7 million , of which $5.0 million is required to be maintained as unused borrowing capacity. Borrowings under the Wells Fargo line are not due until June 30, 2022 as long as the borrowing base is not less than the outstanding amount (See Note 9). Additionally, the Company had $2.3 million of notes payable and $3.0 million of current portion of long-term debt as of March 31, 2019 , which it plans to pay out of its existing available cash. The Company currently believes it will have sufficient resources to fund its currently planned operations and expenditures over the next twelve months without additional financing or other actions. In addition, the Company believes there are a number of ongoing and potential actions that may further strengthen its projected cash and projected financial position. The Company operates in an industry that makes its prospects difficult to evaluate with certainty. Future declines in China market demand or other changes to the Company’s forecasts could adversely affect the Company’s results of operations, financial position and cash flows. As a result, the Company may need to raise additional debt or equity capital to fund its operations. Any additional debt arrangements may likely require regular interest and principal payments which could adversely affect the Company’s operations. There can be no assurance that additional debt or equity capital will be available on acceptable terms, or at all. Certain Significant Risks and Uncertainties The Company operates in a dynamic industry and, accordingly, can be affected by a variety of factors. For example, any of the following areas could have a negative effect on the Company in terms of its future financial position, results of operations or cash flows: the general state of the U.S., China and world economies; the highly cyclical nature of the industries the Company serves; the loss of any of a small number of its larger customers; ability to obtain additional financing; inability to meet certain debt covenants; failure to successfully integrate completed acquisitions; fundamental changes in the technology underlying the Company’s products; the hiring, training and retention of key employees; successful and timely completion of product design efforts; and new product design introductions by competitors. Concentration In the three months ended March 31, 2019 , Huawei Technologies Co. Ltd. and its affiliate HiSilicon Technologies (together with Huawei Technologies Co. Ltd., "Huawei") and one other customer accounted for approximately 49% and 24% of the Company's total revenue, respectively, and the Company’s top five customers represented approximately 87% of the Company’s total revenue. In the three months ended March 31, 2018 , Huawei and one other customer accounted for approximately 48% and 19% of the Company's total revenue, respectively, and the Company’s top five customers represented approximately 84% of the Company’s total revenue. As of March 31, 2019 , three customers accounted for approximately 39% , 17% and 10% of the Company’s accounts receivable. As of December 31, 2018 , two customers accounted for approximately 35% and 17% , respectively, of the Company’s accounts receivable. Use of Estimates The preparation of financial statements in accordance with U.S. 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 financial statements and the reported revenue and expenses during the reporting period. Significant estimates made by management include: the useful lives of property, plant and equipment and intangible assets as well as future cash flows to be generated by those assets; fair values of identifiable assets acquired and liabilities assumed in business combinations; allowances for doubtful accounts; valuation allowances for deferred tax assets; valuation of excess and obsolete inventories; warranty reserves; litigation accrual and recognition of stock-based compensation, among others. Actual results could differ from these estimates. Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use ("ROU") assets, other current liabilities and operating lease liabilities on the Company's consolidated balance sheets. Finance leases are included in property, plant and equipment, current portion of long-term debt and long-term debt, net of current portion on the consolidated balance sheets. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As most of our leases do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on observed market data and other information available at the lease commencement date. The operating lease ROU assets also includes any lease payments made and excludes lease incentives. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. The Company does not record leases on the condensed consolidated balance sheet with a term of one year or less. The Company does not separate lease and non-lease components but rather account for each separate component as a single lease component for all underlying classes of assets. Variable lease payments are expensed as incurred and are not included within the operating lease ROU asset and lease liability calculation. Variable lease payments primarily include reimbursements of costs incurred by lessors for common area maintenance and utilities. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term. Accounting Standards Update Recently Adopted In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-2, Leases (Topic 842) (“ASU 2016-2”). ASU 2016-2 introduces a lessee model that requires recognition of assets and liabilities arising from qualified leases on the consolidated balance sheets and consolidated statements of operations and to disclose qualitative and quantitative information about lease transactions. It is effective for interim and annual periods beginning after December 15, 2018. Certain optional practical expedients are allowed. The Company adopted this standard as of January 1, 2019, using the modified retrospective transition method by applying the new standard to all leases existing at the date of initial application and not restating comparative periods. The Company elected the package of practical expedients permitted under the transition guidance, which allowed the Company to carryforward historical lease classification, assessment on whether a contract was or contains a lease, and initial direct costs for any leases that existed prior to January 1, 2019. The Company also elected to combine lease and non-lease components and to keep leases with an initial term of 12 months or less off the condensed consolidated balance sheet. As a result of adopting Topic 842 on January 1, 2019, the Company recognized operating lease right-of-use assets of $17.3 million and corresponding operating lease liabilities of $20.8 million from existing leases on the Company's condensed consolidated balance sheet. See Note 10 for further details. The adoption of Topic 842 had no impact on the Company's condensed consolidated statement of operations or condensed consolidated statement of cash flows. There have been no other changes in the Company’s significant accounting policies in the three months ended March 31, 2019, as compared to the significant accounting policies described in its Annual Report on Form 10-K for the year ended December 31, 2018 . Recent Accounting Standards Update Not Yet Effective In January 2017, the FASB issued ASU 2017-4, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (“ASU 2017-4”). This standard amends the goodwill impairment test to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, up to the total amount of goodwill allocated to that reporting unit. ASU 2017-4 is effective prospectively for interim and annual periods beginning after December 15, 2019. Early adoption is permitted for interim and annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company has not determined whether it will elect early adoption and is currently evaluating the impact of the adoption of this standard on its consolidated financial statements and related disclosures. 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 amends existing guidance on the impairment of financial assets and adds an impairment model that is based on expected losses rather than incurred losses and requires an entity to recognize as an allowance its estimate of expected credit losses for its financial assets. An entity will apply this guidance through a cumulative-effect adjustment to retained earnings upon adoption (a modified-retrospective approach) while a prospective transition approach is required for debt securities for which an other-than-temporary impairment had been recognized before the effective date. It is effective for the Company’s annual and interim reporting periods beginning after December 15, 2019. Early adoption is permitted. The Company is in the process of evaluating the impact of the adoption on its consolidated financial statements and related disclosures.

Revenue

Revenue	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Revenue	Revenue Product revenue The Company develops, manufactures and sells optoelectronic products that transmit, receive, modify and switch high speed digital optical signals for communications networks. Revenue is derived primarily from the sale of hardware products. The Company sells its products worldwide, primarily to leading network equipment manufacturers. Revenue recognition Revenue is recognized upon transfer of control of promised products or services to customers in an amount that reflects the consideration the Company expects to receive in exchange for those products or services. The Company generally bears all costs, risk of loss or damage and retains title to the goods up to the point of transfer of control of promised products to customer. Revenue related to the sale of consignment inventories at customer vendor managed locations is not recognized until the products are pulled from consignment inventories by customers. In instances where acceptance of the product or solutions is specified by the customer, revenue is deferred until such required acceptance criteria have been met. Shipping and handling costs are included in the cost of goods sold. The Company presents revenue net of sales taxes and any similar assessments. Nature of products Revenue from sale of hardware products is recognized upon transfer of control to the customer. The performance obligation for the sale of hardware products is satisfied at a point in time. The Company has aligned its products in two groups - High Speed Products and Network Products and Solutions. The following presents revenue by product group (in thousands): Three Months Ended March 31, 2019 2018 High Speed Products $ 70,168 $ 59,090 Network Products and Solutions 9,198 9,496 Total revenue $ 79,366 $ 68,586 The following table presents the Company's revenue information by geographical region. Revenue is classified based on the ship to location requested by the customer. Such classification recognizes that for many customers, including those in North America or in Europe, designated shipping points are often in China or elsewhere in Asia (in thousands): Three Months Ended 2019 2018 China $ 45,547 $ 41,672 Americas 13,829 12,208 Rest of world 19,990 14,706 Total revenue $ 79,366 $ 68,586 Certain prior period amounts have been reclassified to conform to the current period presentation. Deferred revenue The Company records deferred revenue when cash payments are received or due in advance of our performance. Refer to Note 7 for disclosure of deferred revenue balances. The increase in the deferred revenue balance during the three months ended March 31, 2019 was immaterial, offset by approximately $0.6 million of revenue recognized during the three months ended March 31, 2019 that was included in the deferred revenue balance as of December 31, 2018 . The increase in the deferred revenue balance during the three months ended March 31, 2018 was immaterial, offset by approximately $0.4 million of revenue recognized that was included in the deferred revenue balance as of December 31, 2017 . Contract assets The Company records contract assets when the revenue is recognized but the customer payment is contingent on a future event. The balance of contract assets as of March 31, 2019 and December 31, 2018 was immaterial. Refund liabilities The Company records refund liabilities when the contract permits the customer to return the product if certain circumstances arise. The balance of refund liabilities as of March 31, 2019 and December 31, 2018 was immaterial.

Net loss per share

Net loss per share	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Net loss per share	Net loss per share The following table sets forth the computation of the basic and diluted net loss per share for the periods indicated (in thousands, except per share amounts): Three Months Ended 2019 2018 Numerator: Net loss $ (14,091 ) $ (18,246 ) Denominator: Weighted average shares used to compute per share amount: Basic 46,414 44,259 Diluted 46,414 44,259 Basic net loss per share $ (0.30 ) $ (0.41 ) Diluted net loss per share $ (0.30 ) $ (0.41 ) The Company has excluded the impact of the following outstanding employee stock options and restricted stock units as well as the shares expected to be issued under its employee stock purchase plan from the computation of diluted net loss per share, as their effect would have been antidilutive (in thousands): March 31, 2019 March 31, 2018 Employee stock options 3,145 3,940 Restricted stock units 2,419 2,377 Market-based restricted stock units 677 — Employee stock purchase plan 414 411 6,655 6,728

Cash, cash equivalents, short-t

Cash, cash equivalents, short-term investments, and restricted cash	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
Cash, cash equivalents, short-term investments, and restricted cash	Cash, cash equivalents, short-term investments, and restricted cash The following table summarizes the Company’s cash, cash equivalents, short-term investments and restricted cash (in thousands): March 31, December 31, Cash and cash equivalents: Cash $ 59,793 $ 58,185 Cash equivalents — — Cash and cash equivalents $ 59,793 $ 58,185 Short-term investments $ 7,524 $ 7,481 Restricted cash $ 11,577 $ 11,053 March 31, December 31, Cash and cash equivalents $ 59,793 $ 58,185 Restricted cash 11,577 11,053 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 71,370 $ 69,238 The following table summarizes the Company’s unrealized gains and losses related to its cash equivalents and short-term investments in marketable securities designated as available-for-sale (in thousands): As of March 31, 2019 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Marketable securities: Money market funds $ 7,524 $ — $ — $ 7,524 $ 7,481 $ — $ — $ 7,481 Reported as: Short-term investments $ 7,524 $ 7,481 As of March 31, 2019 and December 31, 2018 , maturities of marketable securities were less than 1 year. There were no realized gains and losses on the sale of marketable securities during the three months ended March 31, 2019 and 2018. The Company did not recognize any impairment losses on its marketable securities during the three months ended March 31, 2019 or 2018 . As of March 31, 2019 , the Company did not have any investments in marketable securities that were in an unrealized loss position for a period in excess of 12 months.

Fair value disclosures

Fair value disclosures	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair value disclosures	Fair value disclosures Assets and Liabilities Measured at Fair Value on a Recurring Basis The following table presents the Company's assets and liabilities that are measured at fair value on a recurring basis (in thousands): As of March 31, 2019 As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Short-term investments: Money market funds $ 7,524 $ — $ — $ 7,524 $ 7,481 $ — $ — $ 7,481 Other long-term assets: Mutual funds held in Rabbi Trust $ 540 $ — $ — $ 540 $ 465 $ — $ — $ 465 Liabilities Accrued and other current liabilities: Rusnano payment derivative $ — $ — $ 2,000 $ 2,000 $ — $ — $ 2,000 $ 2,000 The Company offers a Non-Qualified Deferred Compensation Plan (“NQDC Plan”) to a select group of its highly compensated employees. The NQDC Plan provides participants the opportunity to defer payment of certain compensation as defined in the NQDC Plan. A Rabbi Trust has been established to fund the NQDC Plan obligation, which was fully funded at March 31, 2019 . The assets held by the Rabbi Trust are substantially in the form of exchange traded mutual funds and are included in the Company’s other long-term assets on its condensed consolidated balance sheets as of March 31, 2019 and December 31, 2018 . Assets and Liabilities Measured at Fair Value on a Nonrecurring Basis As of March 31, 2019 and December 31, 2018 the Company had no assets or liabilities required to be measured at fair value on a nonrecurring basis. Assets and Liabilities Not Measured at Fair Value The carrying values of accounts receivable, accounts payable, notes payable and short-term borrowings approximate their fair values due to the short-term nature and liquidity of these financial instruments. The estimated fair value of the Company's long-term debt approximated its carrying value as of March 31, 2019 and December 31, 2018 , as the interest rates approximated rates currently available to the Company on the issuance of liabilities with a similar maturity. This estimate is considered to be a level 2 fair value measurement.

Asset sale

Asset sale	3 Months Ended
	Mar. 31, 2019
Discontinued Operations and Disposal Groups [Abstract]
Asset sale	Asset Sale In January 2017, the Company completed the sale of its Low Speed Transceiver Products’ assets to APAT OE pursuant to an asset purchase agreement dated December 14, 2016 for consideration of approximately $25.0 million (in RMB equivalent) plus approximately $1.4 million (in RMB equivalent) post-closing transaction service fees to be received under a transition services agreement with APAT OE in which the Company will provide short-term manufacturing and other specific services pursuant to such agreement. The related supply chain purchase commitments and value-added tax obligations have been assumed by APAT OE. The receivable and payable balances related to the transition service arrangement were $12.3 million and $11.8 million , respectively, as of March 31, 2019. As of December 31, 2016, the balance in assets held for sale was $13.9 million , consisting of $13.1 million in inventories and $0.8 million in property, plant and equipment. As a result of post-closing adjustments, total consideration was reduced by approximately $3.4 million for inventory. In addition, an immaterial amount of property, plant and equipment was reclassified from assets held for sale. Upon closing, assets sold to APAT OE were approximately $12.8 million , including approximately $12.1 million in inventories and $0.7 million in property, plant and equipment. The adjusted consideration received of approximately $21.6 million is subject to further reduction of up to $10.0 million for any indemnification claims. As of March 31, 2019, the Company has a reserve of $6.9 million within accrued and other current liabilities for warranty claims. The indemnification warranties expired on June 30, 2017. The Company recognized a $2.2 million gain on the sale of these assets within operating loss in 2017. All of the Low Speed Transceiver Products were part of the Company’s Network Products and Solution product group and included the low speed optical network (PON) products for which the end-of-life plan was announced in mid-2016.

Balance sheet components

Balance sheet components	3 Months Ended
	Mar. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Balance sheet components	Balance sheet components Accounts receivable, net Accounts receivable, net, consists of the following (in thousands): March 31, 2019 December 31, 2018 Accounts receivable $ 63,717 $ 74,343 Trade notes receivable 1,757 672 Allowance for doubtful accounts (264 ) (264 ) $ 65,210 $ 74,751 Inventories, net Inventories, net consist of the following (in thousands): March 31, 2019 December 31, 2018 Raw materials $ 24,727 $ 27,806 Work in process 15,240 13,044 Finished goods (1) 13,651 11,309 $ 53,618 $ 52,159 ________________________________________________________ (1) Finished goods inventory at customer vendor managed inventory locations was $5.5 million and $5.6 million as of March 31, 2019 and December 31, 2018 , respectively. Assets held for sale In December 2018, the Company entered into an agreement with Joint Stock Company Rusnano, a related party, for Joint Stock Company Rusnano group to purchase the 100% interest in the operations of NeoPhotonics Corporation, LLC, the Company's manufacturing operations in Russia. In 2018, the Company recorded additional restructuring expense of $1.6 million related to these operations, bringing the total amount accrued for the Rusnano payment derivative to $2.0 million . As of March 31, 2019, the Company has recorded assets with a carrying value of $3.1 million as held for sale, consisting primarily of $2.6 million of property, plant and equipment and $0.5 million of prepaid expenses and other current assets. The estimated fair value less direct costs of sale approximates the related carrying value. The balance for liabilities held for sale as of March 31, 2019 was immaterial and was primarily included in accrued and other current liabilities. Prepaid expenses and other current assets Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2019 December 31, 2018 Prepaid taxes and taxes receivable $ 4,117 $ 5,461 Transition services agreement receivable (see Note 6) 12,263 11,999 Deposits and other prepaid expenses 2,913 3,020 Other receivable 4,702 6,125 $ 23,995 $ 26,605 Property, plant and equipment, net Purchases of property, plant and equipment unpaid as of March 31, 2019 and March 31, 2018 was $1.8 million and $3.5 million , respectively. Purchased intangible assets Purchased intangible assets consist of the following (in thousands): March 31, 2019 December 31, 2018 Gross Assets Accumulated Amortization Net Assets Gross Accumulated Net Technology and patents $ 37,314 $ (35,457 ) $ 1,857 $ 37,029 $ (34,995 ) $ 2,034 Customer relationships 15,269 (15,269 ) — 15,146 (15,026 ) 120 Leasehold interest 1,269 (390 ) 879 1,238 (374 ) 864 $ 53,852 $ (51,116 ) $ 2,736 $ 53,413 $ (50,395 ) $ 3,018 Amortization expense relating to technology and patents and the leasehold interest intangible assets is included within cost of goods sold and customer relationships within operating expenses. The following table presents details of the amortization expense of the Company’s purchased intangible assets as reported in the condensed consolidated statements of operations (in thousands): Three Months Ended 2019 2018 Cost of goods sold $ 184 $ 203 Operating expenses 119 119 Total $ 303 $ 322 The estimated future amortization expense of purchased intangible assets as of March 31, 2019 , is as follows (in thousands): 2019 (remaining nine months) $ 552 2020 738 2021 645 2022 29 2023 29 Thereafter 743 $ 2,736 Accrued and other current liabilities Accrued and other current liabilities consist of the following (in thousands): March 31, 2019 December 31, 2018 Transition services agreement payables (see Note 6) $ 11,776 $ 11,769 Employee-related 17,504 14,899 Asset sale related contingent liabilities (see Note 6) 6,918 6,751 Operating lease liabilities, current 2,274 — Accrued warranty 739 672 Deferred revenue, current 481 1,114 Income and other taxes payable 1,055 1,580 Rusnano payment derivative 2,000 2,000 Accrued litigation settlement 1,150 2,645 Other accrued expenses 6,372 8,858 $ 50,269 $ 50,288 Warranty Accrual The table below summarizes the movement in the warranty accrual, which is included in accrued and other current liabilities (in thousands): Three Months Ended 2019 2018 Beginning balance $ 672 $ 1,334 Warranty accruals 315 546 Settlements (248 ) (181 ) Ending balance $ 739 $ 1,699 Other noncurrent liabilities Other noncurrent liabilities consist of the following (in thousands): March 31, 2019 December 31, 2018 Pension and other employee-related $ 4,573 $ 4,529 Deferred rent — 3,058 Government grant 1,993 2,108 Capital lease obligation — 282 Asset retirement obligations and other 3,556 3,522 $ 10,122 $ 13,499

Restructuring

Restructuring	3 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Restructuring	Restructuring In 2017, the Company initiated restructuring actions in order to focus on key growth initiatives and to move towards a lower break even revenue level through lower operating expenses and manufacturing cost reductions. Actions included a reduction in force, facilities consolidation and certain asset-related adjustments. The Company recorded restructuring charges of $0.2 million within operating expenses in the three months ended March 31, 2019 . The Company recorded $0.1 million in restructuring charges within cost of goods sold and operating expenses in the three months ended March 31, 2018 . Restructuring activities for the three months ended March 31, 2019 were as follows (in thousands): Employee Severance Facilities Consolidation Others Total Restructuring obligations December 31, 2018 $ 436 $ 769 $ 1,611 $ 2,816 Charges 14 — 165 179 Cash payments (450 ) (47 ) (17 ) (514 ) Adoption of ASC 842 — (620 ) — (620 ) Restructuring obligations March 31, 2019 $ — $ 102 $ 1,759 $ 1,861 The current restructuring liability reported in accrued and other current liabilities in the condensed consolidated balance sheets as of March 31, 2019 was $1.9 million .

Debt

Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Debt	Debt The table below summarizes the carrying amount and weighted average interest rate of the Company’s debt (in thousands, except percentages): March 31, 2019 December 31, 2018 Carrying Amount Interest Rate Carrying Interest Notes payable to suppliers $ 2,339 — $ 4,795 Total notes payable and short-term borrowing $ 2,339 $ 4,795 Long-term debt, current and non-current: Borrowing under Wells Fargo Credit Facility $ 36,306 4.74 % $ 35,961 4.41 % Mitsubishi Bank loans 10,523 1.05% -1.45% 11,094 1.05% -1.45% Mitsubishi Bank and Yamanashi Chou Bank loan 6,572 1.1 % 6,898 1.1 % Finance lease liability 330 — Unaccreted discount and issuance costs (555 ) (602 ) Total long-term debt, net of unaccreted discount and issuance costs $ 53,176 $ 53,351 Reported as: Current portion of long-term debt $ 2,963 $ 2,897 Long-term debt, net of current portion 50,213 50,454 Total long-term debt, net of unaccreted discount and issuance costs $ 53,176 $ 53,351 Notes payable and short-term borrowing The Company regularly issues notes payable to its suppliers in China. These notes are supported by non-interest bearing bank acceptance drafts issued under the Company’s existing line of credit facilities and are due three to six months after issuance. As a condition of the notes payable arrangements, the Company is required to keep a compensating balance at the issuing banks that is a percentage of the total notes payable balance until the amounts are settled. As of March 31, 2019 , the Company’s subsidiary in China had two line of credit facilities with the following banking institutions: • Under the first line of credit facility with Shanghai Pudong Development Bank, the Company can borrow up to RMB 120.0 million ( $17.9 million ) for short-term loans at varying interest rates, or up to approximately RMB 240.0 million ( $35.8 million ) for bank acceptance drafts (with up to 50% compensating balance requirement). This line of credit facility expires in November 2021. In November 2017, the Company borrowed $17.0 million under this line which bore interest at 4.1% . The amount of $17.0 million under this line was repaid in May 2018. • Under the second line of credit facility with Shanghai Pudong Development Bank, which expires in November 2021, the Company can borrow up to RMB 30.0 million ( $4.5 million ) for short-term loans at varying interest rates, or up to approximately RMB 60.0 million ( $8.9 million ) for bank acceptance drafts (with up to 50% compensating balance requirement). • In December 2017, the Company's subsidiary in China entered into a third line of credit facility with China CITIC Bank in China, which expired in November 2018. The purpose of the credit facility is to provide short-term borrowings, bank acceptance drafts and letters of credits. Under this credit facility, the Company can borrow up to approximately RMB 250 million ( $37.2 million ) at varying interest rates, or up to approximately RMB 390.6 million ( $58.2 million ) for bank acceptance drafts (with up to 36% compensating balance requirement). In February 2018, the Company borrowed $17.0 million under this line which bore interest at 4.7% . The amount of $17.0 million under this line was repaid in August 2018. The Company had a line of credit facility previously with China CITIC Bank in China which expired during September 2017. In July 2017, the Company borrowed $17.0 million under this line which bears interest at LIBOR plus 2.55% . The amount of $17.0 million under this line was repaid to CITIC Bank in January 2018. Under these line of credit facilities, the non-interest bearing bank acceptance drafts issued in connection with the Company’s notes payable to its suppliers in China, had an outstanding balance of $2.3 million and $4.8 million as of March 31, 2019 and December 31, 2018 , respectively. As of March 31, 2019 and December 31, 2018 , compensating balances relating to these bank acceptance drafts and letters of credit issued to suppliers and the Company’s subsidiaries totaled $2.6 million and $2.6 million , respectively. Compensating balances are classified as restricted cash on the Company’s condensed consolidated balance sheets. In China, when there is a case pending in judicial court, banks may choose to limit borrowing against existing credit lines, regardless of the legitimacy of the case. The Company has a dispute pending with APAT OE in judicial court (See Note 12). The Company does not expect to make any additional draws against its credit facilities in China until this matter is resolved. Credit facilities In September 2017, the Company entered into a revolving line of credit agreement with Wells Fargo Bank, National Association ("Wells Fargo") as the administrative agent for a lender group (the "Wells Fargo Credit Facility" or "Credit Facility"). The Wells Fargo Credit Facility provides for borrowings equal to the lower of (a) a maximum revolver amount of $50.0 million , or (b) an amount equal to 80% - 85% of eligible accounts receivable plus 100% of qualified cash balances up to $15.0 million , less certain discretionary adjustments ("Borrowing Base"). The maximum revolver amount may be increased by up to $25.0 million , subject to certain conditions. At closing, $50.0 million was available, of which $30.0 million was drawn. The Company used $20.0 million of this amount to pay the principal and interest due under the Comerica Bank Credit Facility, which has since been terminated. The Credit Facility matures on June 30, 2022 and borrowings bear interest at an interest rate option of either (a) the LIBOR rate, plus an applicable margin ranging from 1.50% to 1.75% per annum, or (b) the prime lending rate, plus an applicable margin ranging from 0.50% to 0.75% per annum. The Company is also required to pay a commitment fee equal to 0.25% of the unused portion of the Credit Facility. The Credit Facility agreement ("Agreement") requires prepayment of the borrowings to the extent the outstanding balance is greater than the lesser of (a) the most recently calculated Borrowing Base, or (b) the maximum revolver amount. The Company is required to maintain a combination of certain defined cash balances and unused borrowing capacity under the Credit Facility of at least $20.0 million , of which at least $5.0 million shall include unused borrowing capacity. The Agreement also restricts the Company's ability to dispose of assets, permit change in control, merge or consolidate, make acquisitions, incur indebtedness, grant liens, make investments and make certain restricted payments. Borrowings under the Credit Facility are collateralized by substantially all of the Company's assets. The Company was in compliance with the covenants of this Credit Facility as of March 31, 2019 . As of March 31, 2019 , the outstanding balance under the Credit Facility was $36.3 million and the weighted average rate under the LIBOR option was 4.74% . The remaining borrowing capacity as of March 31, 2019 was $13.7 million , of which $5.0 million is required to be maintained as unused borrowing capacity. The Company repaid $5.0 million in January 2019, which was borrowed in December 2018. The Company repaid $5.0 million in April 2019, which was borrowed in March 2019. Mitsubishi Bank loans On February 25, 2015, the Company entered into certain loan agreements and related agreements with MUFG Bank, Ltd. (the “Mitsubishi Bank”) that provided for (i) a term loan in the aggregate principal amount of 500 million JPY ( $4.4 million ) (the “Term Loan A”) and (ii) a term loan in the aggregate principal amount of one billion JPY ( $9.0 million ) (the “Term Loan B” and together with the Term Loan A, the “2015 Mitsubishi Bank Loans”). The 2015 Mitsubishi Bank Loans are secured by a mortgage on certain real property and buildings owned by the Company’s Japanese subsidiary. Interest on the 2015 Mitsubishi Bank Loans accrues and is paid monthly based upon the annual rate of the monthly Tokyo Interbank Offer Rate (TIBOR) plus 1.40% . The Term Loan A required interest only payments until the maturity date of February 23, 2018, with a lump sum payment of the aggregate principal amount on the maturity date. The Term Loan B requires equal monthly payments of principal equal to 8,333,000 JPY until the maturity date of February 25, 2025, with a lump sum payment of the balance of 8,373,000 JPY on the maturity date. Interest on the Term Loan B is accrued based upon monthly TIBOR plus 1.40% and is secured by real estate collateral. In conjunction with the execution of the Bank Loans, the Company paid a loan structuring fee, including consumption tax, of 40,500,000 JPY ( $0.4 million ). The Term Loan A of 500 million JPY (approximately $4.4 million ) was repaid to the Mitsubishi Bank in January 2018. The 2015 Mitsubishi Bank Loans contain customary representations and warranties and customary affirmative and negative covenants applicable to the Company’s Japanese subsidiary, including, among other things, restrictions on cessation in business, management, mergers or acquisitions. The 2015 Mitsubishi Bank Loans contain financial covenants relating to minimum net assets, maximum ordinary loss and a dividends covenant. Outstanding principal balance for Term Loan B and unamortized debt issuance costs were approximately 591.7 million JPY (approximately $5.3 million ) and 61.5 million JPY (approximately $0.6 million ), respectively, as of March 31, 2019 . The Company was in compliance with the related covenants as of March 31, 2019 and December 31, 2018 . In March 2017, the Company entered into a loan agreement and related agreements with the Mitsubishi Bank for a term loan of 690 million JPY (approximately $6.2 million ) (the “2017 Mitsubishi Bank Loan”) to acquire manufacturing equipment for its Japanese subsidiary. This loan is secured by the manufacturing equipment acquired from the loan proceeds. Interest on the 2017 Mitsubishi Bank Loan is based on the annual rate of the monthly TIBOR rate plus 1.00% . The 2017 Mitsubishi Bank Loan matures on March 29, 2024 and requires monthly interest and principal payments over 72 months commencing in April 2018. The loan contains customary covenants relating to minimum net assets, maximum ordinary loss and a dividends covenant. The Company was in compliance with these covenants as of March 31, 2019 . The loan was available from March 31, 2017 to March 30, 2018 and 690 million JPY (approximately $6.2 million ) under this loan was fully drawn in March 2017. Mitsubishi Bank and Yamanashi Chou Bank loan In January 2018, the Company entered into a term loan agreement with Mitsubishi Bank and The Yamanashi Chou Bank, Ltd. for a term loan in the aggregate principal amount of 850 million JPY (approximately $7.7 million ) (the “Term Loan C”). The purpose of the Term Loan C is to obtain machinery for the core parts of the manufacturing line and payments for related expenses by the Company's subsidiary in Japan. The Term Loan C is secured by the assets owned by the Company's subsidiary in Japan. The Term Loan C was available from January 29, 2018 to January 29, 2025. The full amount of the Term Loan C was drawn in January 2018. Interest on the Term Loan C is based upon the annual rate of the three months TIBOR rate plus 1.00% . The Term Loan C requires quarterly interest payments, along with the principal payments, over 82 months commencing in April 2018. The Term Loan C loan agreement contains customary representations and warranties and customary affirmative and negative covenants applicable to the Japanese Subsidiary, including, among other things, restrictions on cessation in business, management, mergers or acquisitions. The Term Loan C loan agreement contains financial covenants relating to minimum net assets and maximum ordinary loss. The Company was in compliance with these covenants as of March 31, 2019 . As of March 31, 2019 , maturities of total long-term debt were as follows (in thousands): 2019 (remaining nine months) $ 2,338 2020 3,122 2021 3,129 2022 39,425 2023 3,034 Thereafter 2,683 $ 53,731

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	Leases The Company has operating leases for offices, research and development facilities and manufacturing facilities. Leases have remaining terms of less than one year to nine years, some of which include options to extend the leases and some of which may include options to terminate the leases within 1 year. As of March 31, 2019 and December 31, 2018, an asset recorded in property, plant and equipment under a finance lease was immaterial. The components of lease expense were as follows (in thousands): Three Months Ended 2019 Operating lease cost $ 754 Variable and short-term lease cost 348 Total lease cost $ 1,102 Other information related to leases was as follows (in thousands, except lease term and discount rate): Three Months Ended 2019 Supplemental cash flow information Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 835 Weighted average remaining lease term Operating leases 7.9 years Weighted average discount rate Operating leases 6.4 % Future minimum lease payments under non-cancellable leases as of March 31, 2019 were as follows (in thousands): Operating Leases 2019 (excluding the three months ended March 31, 2019) $ 2,773 2020 3,129 2021 3,074 2022 3,065 2023 3,014 Thereafter 11,194 Total future minimum lease payments 26,249 Less imputed interest (5,956 ) Total $ 20,293 Reported as of March 31, 2019: Operating Leases Accrued and other current liabilities $ 2,274 Operating lease liabilities, noncurrent 18,019 Total $ 20,293 As of December 31, 2018, the future minimum commitments under the Company’s non-cancelable operating leases and capital leases are as follows (in thousands): Operating Leases 2019 $ 3,618 2020 3,113 2021 3,059 2022 3,056 2023 3,049 Thereafter 11,437 Total future minimum lease payments $ 27,332

Japan pension plan

Japan pension plan	3 Months Ended
	Mar. 31, 2019
Retirement Benefits [Abstract]
Japan pension plan	Japan pension plan The pension liability related to the Company’s Retirement Allowance Plan (“RAP”) in Japan as of March 31, 2019 was $4.0 million which was recorded in other noncurrent liabilities on the Company’s condensed consolidated balance sheet. The pension liability related to the Company’s RAP in Japan as of December 31, 2018 was $4.3 million , of which $0.3 million , was recorded in accrued and other current liabilities and the remainder in other noncurrent liabilities on the Company’s condensed consolidated balance sheet. Net periodic pension cost associated with this plan was immaterial in the three months ended March 31, 2019 and 2018 .

Commitments and contingencies

Commitments and contingencies	3 Months Ended
	Mar. 31, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and contingencies	Commitments and contingencies Litigation From time to time, the Company is subject to various claims and legal proceedings, either asserted or unasserted, that arise in the ordinary course of business. The Company accrues for legal contingencies if the Company can estimate the potential liability and if the Company believes it is probable that the case will be ruled against it. If a legal claim for which the Company did not accrue is resolved against it, the Company would record the expense in the period in which the ruling was made. The Company believes that the likelihood of an ultimate amount of liability, if any, for any pending claims of any type (alone or combined) that will materially affect the Company’s financial position, results of operations or cash flows is remote. The ultimate outcome of any litigation is uncertain, however, and unfavorable outcomes could have a material negative impact on the Company’s financial condition and operating results. Regardless of outcome, litigation can have an adverse impact on the Company because of defense costs, negative publicity, diversion of management resources and other factors. In January 2010, Finisar Corporation, or Finisar, filed a complaint in the U.S. District Court for the Northern District of California, or the Court, against Source Photonics, Inc., MRV Communications, Inc., Oplink Communications, Inc. and the Company, or collectively, the co-defendants. In the complaint Finisar alleged infringement of certain of its U.S. patents. In 2010 the Company filed an answer to the complaint and counterclaims, asserting two claims of patent infringement and additional claims. The Court dismissed without prejudice all co-defendants (including the Company) except Source Photonics, Inc., on grounds that such claims should have been asserted in four separate lawsuits, one against each defendant. This dismissal does not prevent Finisar from bringing a new similar lawsuit against the Company. In 2011 the Company and Finisar agreed to suspend their respective claims and in 2012 the Company and Finisar further agreed to toll their respective claims. While there has been no action on this matter since 2012, the Company is currently unable to predict the outcome of this dispute and therefore cannot determine the likelihood of loss nor estimate a range of possible loss. In December 2016, the Company was served with a lawsuit filed by Lestina International Ltd. (“Lestina”), in Santa Clara County, CA. The lawsuit is regarding a dispute of approximately $3.0 million related to purchase orders for the Company’s Low Speed Transceiver Products that was soon thereafter sold by the Company to APAT OE in January 2017. The purchase orders in question were included in the asset sale and were assumed liabilities by the purchaser of the business. The parties engaged in extensive negotiations and in January 2019, the parties agreed to a proposed settlement which was placed on the record of the Superior Court of Santa Clara County agreeing that NeoPhotonics Dongguan Co., Ltd. (“NeoDongguan”) (the Company’s wholly owned subsidiary located in China) would pay to Lestina a total of $2.2 million . Upon Lestina's receipt of full payment, Lestina will ship to NeoDongguan the remaining parts from the original purchase orders. The Company has agreed to be a guarantor for NeoDongguan on the payment obligation to Lestina. $1.2 million of the $2.2 million settlement was paid in February 2019 with the balance of $1.0 million to be paid in June 2019. In April 2018, APAT OE filed a lawsuit in the Qianhai Court in Shenzhen, China against NeoPhotonics (China) Co., Ltd. and NeoPhotonics Dongguan Co. Ltd. (collectively "NeoChina") and NeoPhotonics Corporation with a claim of approximately $20.0 million . The lawsuit is in reference to the sale of the low speed transceiver business to APAT OE from NeoChina. APAT OE claims that the business has been losing money and that APAT OE was not given all of the information about the business they purchased prior to signing the Asset Purchase Agreement. In May 2018, counsel on behalf of NeoChina filed a motion objecting to the jurisdiction, claiming that the proper jurisdiction for any dispute between these parties is the Shenzhen Court of International Arbitration (or the "Arbitration Court") and the proper parties to this dispute are NeoChina and APAT OE, pursuant to the Asset Purchase Agreement signed by APAT OE and NeoChina (or the "APA"). In June 2018 a hearing was held in the Qianhai Court in Shenzhen, China and in August 2018 the Court ruled in favor of APAT OE. In October 2018, a hearing was held in the Intermediate Court of Shenzhen (or the "Intermediate Court") on an appeal which was filed by NeoChina and in November 2018 the Intermediate Court ruled in favor of NeoChina and dismissed in totality the litigation against NeoChina, ruling that arbitration was the proper forum for such dispute resolution between the parties. The litigation continues against NeoPhotonics Corporation in Intermediate Court, where NeoPhotonics Corporation claims that there is no existing contract between APAT OE and NeoPhotonics Corporation and therefore there is no basis for litigation. The Company is unable to predict the outcome of this matter and is not currently aware of the precise amount of the ongoing claim by APAT against the remaining defendant, NeoPhotonics Corporation, in this lawsuit. In December 2018, APAT OE officially filed claims through two lawsuits against NeoChina, NeoPhotonics Corporation Limited Hong Kong (or NeoHK), Novel Centennial Limited BVI (or NeoBVI) and NeoPhotonics Corporation in the Intermediate Court in addition to a pre-trial preservation order. On the same day the Court issued the order to preserve approximately $29.0 million of NeoChina assets, which is the approximate amount of the revised claims by APAT OE against all defendants in the first lawsuit. The temporary pre-trial preservation order was made simultaneously to the filing of the two lawsuits, but the defendants were not served or aware of the lawsuit until later in January, 2019. In the first lawsuit, the legal claims are the same as the ones APAT OE filed on April 21, 2018 in Qianhai Court in Shenzhen, China (as described above). The difference is that instead of distributing claims in separate cases, APAT OE has combined its claims to one single case and added the additional defendants of NeoHK and NeoBVI and increased the claimed damages to approximately $29.0 million . In the second lawsuit, the claims are new and related to the alleged new issues related to a contract manufacturer located in the Philippines and claiming damages in the amount of RMB 50.9 million (approximately $7.6 million ). APAT OE claims that the defendants have interfered with APAT OE’s ability to sign an engagement agreement with the contract manufacturer. Defendants believe this dispute is related to and should be under the jurisdiction that was agreed to in the APA, and therefore should be properly transferred to the Shenzhen Court of International Arbitration. In March 2019 the Shenzhen Intermediate Court assigned a judge for the two lawsuits, but no hearing date has been set yet. The Company is unable to predict the outcome of this matter. In February 2019, NeoChina filed a case in the Qianhai Court in Shenzhen, China against APAT OE and Zhejiang Merchants Property Insurance Company for losses and damages caused to NeoChina from APAT OE’s previously granted property preservation. The claim is for approximately RMB 350,000 (approximately $52,000 ) in damages and legal fees and scheduled to be heard on or about May 8, 2019. The Company is unable to predict the outcome of this matter. APAT Arbitration In June 2017, APAT OE filed an arbitration claim in the Shenzhen Court of International Arbitration (or the Arbitration Court) against NeoChina (collectively both of the Company’s China subsidiaries), claiming that approximately $1.5 million of the inventory that was sold to APAT OE by NeoChina in an Asset Purchase Agreement executed between the parties on December 14, 2016 was aged inventory and of no value. The arbitration was heard in the Arbitration Court in August 2017. In October 2017, NeoChina was informed that it was successful in the defense of the dispute and was also successful in its counterclaim against APAT OE. NeoChina was awarded approximately RMB 700,000 (approximately $110,000 ) in compensatory damages and attorney fees as well as having the approximately $1.5 million claim against it rejected in its entirety. In April 2018, APAT OE filed a Notice of Judicial Review of the arbitration judgment in the Shenzhen Intermediate Court in Shenzhen, China. The case was heard in May 2018, and NeoChina was successful in disputing the Judicial Review, which means that the arbitration judgment against APAT OE and in favor of NeoChina stands. In July 2018, NeoChina applied together to the Shenzhen Intermediate Court for enforcement of the previous arbitration ruling because APAT OE had refused to perform the arbitral award. In October 2018, the Court enforced the award officially closing this arbitration matter. In July 2018, NeoChina filed an arbitration claim against APAT OE in the Arbitration Court claiming approximately USD $12.0 million in damages as related to liability under the APA. NeoChina also was granted a property preservation of APAT OE’s bank accounts. In February 2019 NeoChina applied to the Arbitration Court to reduce the claim to USD $7.1 million according to the evidence of confirmation requests received by NeoChina. The case is awaiting a hearing date. The Company is unable to predict the outcome of this matter. In November 2018, APAT OE filed an additional arbitration claim against NeoChina and NeoPhotonics Corporation claiming approximately USD $7.8 million for liability under the APA. In March 2019, NeoChina filed a response and counterclaim against APAT OE including a claim for attorney fees in the amount of RMB 810,000 (approximately $121,000 ). No hearing has been scheduled yet. The Company is unable to predict the outcome of this matter. Indemnifications In the normal course of business, the Company enters into agreements that contain a variety of representations and warranties and provide for general indemnification. The Company’s exposure under these agreements is unknown because it involves claims that may be made against the Company in the future, but have not yet been made. To date, the Company has not paid any claims or been required to defend any action related to its indemnification obligations. However, the Company may record charges in the future as a result of these indemnification obligations. In November 2016, Oyster Communications, Inc. filed nine patent lawsuits against several defendants in the U.S. District Court for the Eastern District of Texas, including one against Cisco Systems, Inc. ("Cisco"). One defendant successfully transferred their case to the U.S. District Court for the Northern District of California. Additional defendants requested venue changes are still pending. The Company was not named as a defendant in any of the lawsuits. In July 2017, Cisco notified the Company that it would be seeking indemnification from the Company for claims against Cisco arising from the lawsuits and the parties engaged in discussions and negotiations. In September 2018, the Company and Cisco signed a settlement agreement under which the Company agreed to pay to Cisco $300,000 , which was paid in January 2019, and $150,000 in product credits to be applied during calendar year 2019. This settlement resolves Cisco's indemnification claims against the Company in this matter. Penalty Payment Derivative In connection with a private placement transaction with Joint Stock Company "Rusnano" (formerly Open Joint Stock Company “RUSNANO"), or Rusnano, in 2012, the Company agreed to certain performance obligations including establishing a wholly-owned subsidiary in Russia and making a $30.0 million investment commitment (the "Investment Commitment") towards the Company’s Russian operations, which could be partially satisfied by cash and/or non-cash investment inside or outside of Russia and/or by way of non-cash asset transfers. The Rights Agreement as amended in 2015 (the "Amended Rights Agreement") limits the maximum amount of penalties and/or exit fee (the "Rusnano Payment") to be paid by the Company to $5.0 million in the aggregate and allows such payment to be reduced when certain milestones are met over time. The Amended Rights Agreement also provides for an updated investment plan for the Company’s Russian subsidiaries that includes non-cash transfer of licensing rights to intellectual property, non-cash transfers of existing equipment and commitments to complete the remaining investment milestones through 2019. As of March 31, 2019, the remaining Investment Commitment was approximately $6.5 million to be invested at any time on or before December 31, 2019. At any point between March 31, 2019 and December 31, 2019, the Company may elect to pay a $2.0 million exit fee to terminate any remaining obligations associated with the Investment Commitment. Rusnano has non-transferable veto rights over the Company’s Russian subsidiaries’ annual budget during the investment period and must approve non-cash asset transfers to be made in satisfaction of the Investment Commitment. The Company accounted for the Rusnano Payment as an embedded derivative instrument. The fair value of the penalty payment derivative has been estimated at the date of the original common stock sale (April 27, 2012) and at each subsequent balance sheet date using a probability-weighted discounted future cash flow approach using unobservable inputs, which are classified as Level 3 within the fair value hierarchy. The primary inputs for this approach include the probability of achieving the Investment Commitment and a discount rate that approximates the Company’s incremental borrowing rate. After the initial measurement, changes in the fair value of this derivative are recorded in other income (expense), net. The estimated fair value of this derivative was $2.0 million as of March 31, 2019 and $2.0 million as of December 31, 2018 . As of March 31, 2019 , and December 31, 2018, the derivative was reported within Accrued and other current liabilities on the Company’s condensed consolidated balance sheets. See Note 7. In December 2018, the Company signed a definitive agreement with Rusnano to sell the Company’s 100% interest in NeoPhotonics Corporation, LLC, the subsidiary for the Company’s manufacturing operations in Russia, for approximately book value. The purchase price to be paid by Rusnano will consist of approximately $3.0 million in cash and $1.0 million in cancellation of the remaining penalty payment that would otherwise be owed to Rusnano as consideration for the Company's obligations to provide manufacturing process transition to NeoPhotonics Corporation, LLC. In April 2019, the Company completed the sale of 100% interest in the operations of NeoPhotonics Corporation, LLC, the Company's manufacturing operations in Russia to Rusnano.

Stockholders' equity

Stockholders' equity	3 Months Ended
	Mar. 31, 2019
Stockholders' Equity Note [Abstract]
Stockholders’ equity	Stockholders’ equity Common Stock As of March 31, 2019 , the Company had reserved 9,032,639 common stock for issuance under its equity incentive plans and 574,462 common stock shares for issuance under its employee stock purchase plan. Accumulated Other Comprehensive Income (loss) The components of accumulated other comprehensive income (loss), net of related taxes, were as follows (in thousands): Foreign Currency Translation Adjustments Defined Benefit Pension Plan Adjustment Total Accumulated Other Comprehensive Income (loss) Balance as of December 31, 2018 $ (6,897 ) $ (229 ) $ (7,126 ) Other comprehensive income (loss), net of taxes of zero and reclassifications 2,937 — 2,937 Balance as of March 31, 2019 $ (3,960 ) $ (229 ) $ (4,189 ) No material amounts were reclassified out of accumulated other comprehensive income during the three months ended March 31, 2019 and 2018 for realized gains or losses on available-for-sale securities. Accumulated Deficit Approximately $9.0 million of the Company’s retained earnings within its total accumulated deficit as of December 31, 2018 was subject to restriction due to the fact that the Company’s subsidiaries in China are required to set aside at least 10% of their respective accumulated profits each year end to fund statutory common reserves as well as allocate a discretional portion of their after-tax profits to their staff welfare and bonus fund.

Stock-based compensation

Stock-based compensation	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-based compensation	Stock-based compensation The following table summarizes the stock-based compensation expense recognized in the three months ended March 31, 2019 and 2018 (in thousands): Three Months Ended 2019 2018 Cost of goods sold $ 601 $ 650 Research and development 881 773 Sales and marketing 678 938 General and administrative 1,178 986 $ 3,338 $ 3,347 Determining Fair Value The Company estimated the fair value of certain stock-based awards using a Black-Scholes-Merton valuation model with the following assumptions: Three Months Ended Stock options 2019 2018 Weighted-average expected term (years) — 6.00 Weighted-average volatility — 65% Risk-free interest rate — 2.27% Expected dividends — —% Stock appreciation units Weighted-average expected term (years) 1.67 2.10 Weighted-average volatility 64% 67% Risk-free interest rate 2.45%-2.63% 1.03% - 1.98% Expected dividends —% —% ESPP Weighted-average expected term (years) 0.73 0.73 Weighted-average volatility 61% 61% Risk-free interest rate 2.36% - 2.59% 1.20% - 1.31% Expected dividends —% —% Stock Options and Restricted Stock Units (RSUs) The following table summarizes the Company’s stock option and RSU activity, excluding market-based RSUs, during the three months ended March 31, 2019: Stock Options Restricted Stock Units Number of Shares Weighted Average Exercise Price Number of Weighted Balance as of December 31, 2018 3,202,745 $ 5.73 2,486,028 $ 7.87 Granted — — 33,598 7.10 Exercised/Converted (47,730 ) 3.50 (41,627 ) 7.88 Cancelled/Forfeited (9,688 ) 11.53 (59,100 ) 8.13 Balance as of March 31, 2019 3,145,327 5.75 2,418,899 7.85 At March 31, 2019, the Company had $1.4 million of unrecognized stock-based compensation expense for stock options, net of estimated forfeitures, which will be recognized over the remaining weighted-average period of 1.6 years. At March 31, 2019, the Company had $11.1 million of unrecognized stock-based compensation expense for RSUs, excluding market-based RSUs, net of estimated forfeitures, which will be recognized over the remaining weighted-average period of 1.9 years. Market-based Restricted Stock Units In 2018, the Company granted 695,000 shares of market-based RSUs to certain employees. These RSUs will vest if the 30-day weighted average closing price of the Company's common stock is equal to or greater than certain price targets per share and the recipients remain in continuous service with the Company through such service period. No market-based RSUs have vested and 17,500 market-based RSUs have been cancelled through March 31, 2019. The weighted average grant-date fair value per share of market-based RSUs granted during 2018 was approximately $5.82 per share. As of March 31, 2019, the Company had $2.5 million of unrecognized stock-based compensation expense for these RSUs, net of estimated forfeitures, which will be recognized over the remaining weighted-average period of 3.26 years. The fair value of market-based RSUs was measured on the grant date using Monte Carlo simulation model with the following assumptions: Year Ended Market-based restricted stock units 2018 Weighted-average volatility 66% Risk-free interest rate 2.79% Expected dividends —% Stock Appreciation Units (SAU) SAUs are liability classified share-based awards. Outstanding SAUs are re-measured each reporting period at fair value until settlement. The Company did not grant any SAUs during the three months ended March 31, 2019 or 2018 . As of March 31, 2019 and December 31, 2018 , there were 191,066 and 192,872 SAUs outstanding, respectively, and related SAU liabilities were $0.6 million and $0.6 million , respectively. Employee Stock Purchase Plan (ESPP) As of March 31, 2019 , there was $0.4 million of unrecognized stock-based compensation expense for employee stock purchase rights that will be recognized over the remaining offering period through November 2019.

Income taxes

Income taxes	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Income taxes	Income taxes The provision for income taxes in the periods presented is based upon the income (loss) before income taxes (in thousands): Three Months Ended 2019 2018 Provision for income taxes $ (170 ) $ (638 ) The Company’s income tax (provision) benefit in the three months ended March 31, 2019 and 2018 was primarily related to income taxes of the Company’s non-U.S. operations. The Company conducts its business globally and its operating income is subject to varying rates of tax in the U.S., China and Japan. Consequently, the Company’s effective tax rate is dependent upon the geographic distribution of its earnings or losses and the tax laws and regulations in each geographical region. Historically, the Company has experienced net losses in the U.S. and in the short term, expects this trend to continue. Due to historical losses in the U.S., the Company has a full valuation allowance on its U.S. federal and state deferred tax assets. Management continues to evaluate the realizability of deferred tax assets and the related valuation allowance. If management's assessment of the deferred tax assets or the corresponding valuation allowance were to change, the Company would record the related adjustment to income during the period in which management makes the determination. On December 22, 2017, the Tax Cuts and Jobs Act (the “TCJA”) was enacted which, among other things, lowered the U.S. federal corporate income tax rate from 35% to 21%, requires companies to pay a one-time transition tax on earnings of certain foreign subsidiaries that were previously tax deferred and creates Global Intangible Low Taxed Income ("GILTI") to tax certain foreign sourced earnings. As of December 31, 2018, the Company has concluded the accounting under the TCJA within the time period set forth in Staff Accounting Bulletin 118. There was no provision impact of TCJA on the 2018 financial statements due to full valuation allowance on US deferred tax assets. In addition, the Company has elected to treat GILTI inclusion accounting impact as a current period expense. As of March 31, 2019, the TCJA has no material impact on the financial statements due to full valuation allowance on US deferred tax assets. The Company adopted ASU 2016-16 on a modified retrospective basis effective January 1, 2018. Upon adoption of this standard on January 1, 2018, the Company recorded $1.8 million to accumulated deficit balance for intra-entity transfer of an asset other than inventory in prior years. As of March 31, 2019 , there were no material changes to either the nature or the amounts of the uncertain tax positions previously determined for the year ended December 31, 2018 .

Subsequent events

Subsequent events	3 Months Ended
	Mar. 31, 2019
Subsequent Events [Abstract]
Subsequent events	Subsequent events In April 2019, the Company repaid $5.0 million to Wells Fargo under the Credit Facility. In April 2019, the Company completed the sale of 100% interest in the operations of NeoPhotonics Corporation, LLC, the Company's manufacturing operations in Russia to Joint Stock Company Rusnano, a related party. In connection with the sale, the Company received $2.0 million in cash and settled the $2.0 million exit fee.

Basis of presentation and sig_2

Basis of presentation and significant accounting policies (Policies)	3 Months Ended
	Mar. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Consolidation	Basis of Presentation and Consolidation The condensed consolidated financial statements of NeoPhotonics Corporation (“NeoPhotonics” or the “Company”) as of March 31, 2019 and for the three months ended March 31, 2019 and 2018 , have been prepared in accordance with the instructions on Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”). In accordance with those rules and regulations, the Company has omitted certain information and notes normally provided in the Company’s annual consolidated financial statements. In the opinion of management, the condensed consolidated financial statements contain all adjustments, consisting only of normal recurring items, except as otherwise noted, necessary for the fair presentation of the Company’s financial position and results of operations for the interim periods. The year-end condensed consolidated balance sheet data was derived from audited consolidated financial statements, but does not include all disclosures required by U.S. generally accepted accounting principles (“U.S. GAAP”). These condensed consolidated financial statements should be read in conjunction with the Consolidated Financial Statements and Notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 . The results of operations for the three months ended March 31, 2019 are not necessarily indicative of the results expected for the entire fiscal year. All intercompany accounts and transactions have been eliminated.
Going Concern	Going Concern Accounting Standards Update (“ASU”) No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern , requires an entity to disclose information about its potential inability to continue as a going concern when conditions and events indicate that it is probable that the entity may be unable to meet its obligations as they become due within one year. Management has assessed the Company’s ability to continue as a going concern within one year of the filing date of this Quarterly Report on Form 10-Q with the SEC in May 2019. The accompanying unaudited condensed consolidated financial statements have been prepared assuming that the Company will continue as a going concern, which contemplates the realization of assets and satisfaction of liabilities in the normal course of business.
Certain Significant Risks And Uncertainties	Certain Significant Risks and Uncertainties The Company operates in a dynamic industry and, accordingly, can be affected by a variety of factors. For example, any of the following areas could have a negative effect on the Company in terms of its future financial position, results of operations or cash flows: the general state of the U.S., China and world economies; the highly cyclical nature of the industries the Company serves; the loss of any of a small number of its larger customers; ability to obtain additional financing; inability to meet certain debt covenants; failure to successfully integrate completed acquisitions; fundamental changes in the technology underlying the Company’s products; the hiring, training and retention of key employees; successful and timely completion of product design efforts; and new product design introductions by competitors.
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with U.S. 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 financial statements and the reported revenue and expenses during the reporting period. Significant estimates made by management include: the useful lives of property, plant and equipment and intangible assets as well as future cash flows to be generated by those assets; fair values of identifiable assets acquired and liabilities assumed in business combinations; allowances for doubtful accounts; valuation allowances for deferred tax assets; valuation of excess and obsolete inventories; warranty reserves; litigation accrual and recognition of stock-based compensation, among others. Actual results could differ from these estimates.
Leases	Leases The Company determines if an arrangement is a lease at inception. Operating leases are included in operating lease right-of-use ("ROU") assets, other current liabilities and operating lease liabilities on the Company's consolidated balance sheets. Finance leases are included in property, plant and equipment, current portion of long-term debt and long-term debt, net of current portion on the consolidated balance sheets. Operating lease ROU assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. As most of our leases do not provide an implicit rate, the Company uses an estimate of its incremental borrowing rate based on observed market data and other information available at the lease commencement date. The operating lease ROU assets also includes any lease payments made and excludes lease incentives. Lease terms may include options to extend or terminate the lease when it is reasonably certain that the Company will exercise such options. The Company does not record leases on the condensed consolidated balance sheet with a term of one year or less. The Company does not separate lease and non-lease components but rather account for each separate component as a single lease component for all underlying classes of assets. Variable lease payments are expensed as incurred and are not included within the operating lease ROU asset and lease liability calculation. Variable lease payments primarily include reimbursements of costs incurred by lessors for common area maintenance and utilities. Lease expense for minimum lease payments is recognized on a straight-line basis over the lease term.
Accounting Standards Update Recently Adopted/Recent Accounting Standards Update Not Yet Effective	Accounting Standards Update Recently Adopted In February 2016, the Financial Accounting Standards Board ("FASB") issued ASU 2016-2, Leases (Topic 842) (“ASU 2016-2”). ASU 2016-2 introduces a lessee model that requires recognition of assets and liabilities arising from qualified leases on the consolidated balance sheets and consolidated statements of operations and to disclose qualitative and quantitative information about lease transactions. It is effective for interim and annual periods beginning after December 15, 2018. Certain optional practical expedients are allowed. The Company adopted this standard as of January 1, 2019, using the modified retrospective transition method by applying the new standard to all leases existing at the date of initial application and not restating comparative periods. The Company elected the package of practical expedients permitted under the transition guidance, which allowed the Company to carryforward historical lease classification, assessment on whether a contract was or contains a lease, and initial direct costs for any leases that existed prior to January 1, 2019. The Company also elected to combine lease and non-lease components and to keep leases with an initial term of 12 months or less off the condensed consolidated balance sheet. As a result of adopting Topic 842 on January 1, 2019, the Company recognized operating lease right-of-use assets of $17.3 million and corresponding operating lease liabilities of $20.8 million from existing leases on the Company's condensed consolidated balance sheet. See Note 10 for further details. The adoption of Topic 842 had no impact on the Company's condensed consolidated statement of operations or condensed consolidated statement of cash flows. There have been no other changes in the Company’s significant accounting policies in the three months ended March 31, 2019, as compared to the significant accounting policies described in its Annual Report on Form 10-K for the year ended December 31, 2018 . Recent Accounting Standards Update Not Yet Effective In January 2017, the FASB issued ASU 2017-4, Intangibles-Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (“ASU 2017-4”). This standard amends the goodwill impairment test to compare the fair value of a reporting unit with its carrying amount and recognize an impairment charge for the amount by which the carrying amount exceeds the reporting unit’s fair value, up to the total amount of goodwill allocated to that reporting unit. ASU 2017-4 is effective prospectively for interim and annual periods beginning after December 15, 2019. Early adoption is permitted for interim and annual goodwill impairment tests performed on testing dates after January 1, 2017. The Company has not determined whether it will elect early adoption and is currently evaluating the impact of the adoption of this standard on its consolidated financial statements and related disclosures. 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 amends existing guidance on the impairment of financial assets and adds an impairment model that is based on expected losses rather than incurred losses and requires an entity to recognize as an allowance its estimate of expected credit losses for its financial assets. An entity will apply this guidance through a cumulative-effect adjustment to retained earnings upon adoption (a modified-retrospective approach) while a prospective transition approach is required for debt securities for which an other-than-temporary impairment had been recognized before the effective date. It is effective for the Company’s annual and interim reporting periods beginning after December 15, 2019. Early adoption is permitted. The Company is in the process of evaluating the impact of the adoption on its consolidated financial statements and related disclosures.

Revenue (Tables)

Revenue (Tables)	3 Months Ended
	Mar. 31, 2019
Revenue from Contract with Customer [Abstract]
Summary of Revenue by Product Group and Geographical Region	The following presents revenue by product group (in thousands): Three Months Ended March 31, 2019 2018 High Speed Products $ 70,168 $ 59,090 Network Products and Solutions 9,198 9,496 Total revenue $ 79,366 $ 68,586 The following table presents the Company's revenue information by geographical region. Revenue is classified based on the ship to location requested by the customer. Such classification recognizes that for many customers, including those in North America or in Europe, designated shipping points are often in China or elsewhere in Asia (in thousands): Three Months Ended 2019 2018 China $ 45,547 $ 41,672 Americas 13,829 12,208 Rest of world 19,990 14,706 Total revenue $ 79,366 $ 68,586

Net loss per share (Tables)

Net loss per share (Tables)	3 Months Ended
	Mar. 31, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Income per Share	The following table sets forth the computation of the basic and diluted net loss per share for the periods indicated (in thousands, except per share amounts): Three Months Ended 2019 2018 Numerator: Net loss $ (14,091 ) $ (18,246 ) Denominator: Weighted average shares used to compute per share amount: Basic 46,414 44,259 Diluted 46,414 44,259 Basic net loss per share $ (0.30 ) $ (0.41 ) Diluted net loss per share $ (0.30 ) $ (0.41 )
Potentially Dilutive Securities Excluded from Computation of Diluted Net Income per Share Attributable to Common Stockholders	The Company has excluded the impact of the following outstanding employee stock options and restricted stock units as well as the shares expected to be issued under its employee stock purchase plan from the computation of diluted net loss per share, as their effect would have been antidilutive (in thousands): March 31, 2019 March 31, 2018 Employee stock options 3,145 3,940 Restricted stock units 2,419 2,377 Market-based restricted stock units 677 — Employee stock purchase plan 414 411 6,655 6,728

Cash, cash equivalents, short_2

Cash, cash equivalents, short-term investments, and restricted cash (Tables)	3 Months Ended
	Mar. 31, 2019
Cash and Cash Equivalents [Abstract]
Summary of Cash, Cash Equivalents and Short-Term investments and Restricted Cash and Investments	The following table summarizes the Company’s cash, cash equivalents, short-term investments and restricted cash (in thousands): March 31, December 31, Cash and cash equivalents: Cash $ 59,793 $ 58,185 Cash equivalents — — Cash and cash equivalents $ 59,793 $ 58,185 Short-term investments $ 7,524 $ 7,481 Restricted cash $ 11,577 $ 11,053 March 31, December 31, Cash and cash equivalents $ 59,793 $ 58,185 Restricted cash 11,577 11,053 Total cash, cash equivalents and restricted cash shown in the statement of cash flows $ 71,370 $ 69,238
Summary of Unrealized Gains and Losses Related to Cash Equivalents and Investments in Marketable Securities	The following table summarizes the Company’s unrealized gains and losses related to its cash equivalents and short-term investments in marketable securities designated as available-for-sale (in thousands): As of March 31, 2019 As of December 31, 2018 Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Amortized Cost Gross Unrealized Gains Gross Unrealized Loss Fair Value Marketable securities: Money market funds $ 7,524 $ — $ — $ 7,524 $ 7,481 $ — $ — $ 7,481 Reported as: Short-term investments $ 7,524 $ 7,481

Fair value disclosures (Tables)

Fair value disclosures (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Fair Value of Financial Assets	The following table presents the Company's assets and liabilities that are measured at fair value on a recurring basis (in thousands): As of March 31, 2019 As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Short-term investments: Money market funds $ 7,524 $ — $ — $ 7,524 $ 7,481 $ — $ — $ 7,481 Other long-term assets: Mutual funds held in Rabbi Trust $ 540 $ — $ — $ 540 $ 465 $ — $ — $ 465 Liabilities Accrued and other current liabilities: Rusnano payment derivative $ — $ — $ 2,000 $ 2,000 $ — $ — $ 2,000 $ 2,000
Fair Value of Financial Liabilities	The following table presents the Company's assets and liabilities that are measured at fair value on a recurring basis (in thousands): As of March 31, 2019 As of December 31, 2018 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Assets Short-term investments: Money market funds $ 7,524 $ — $ — $ 7,524 $ 7,481 $ — $ — $ 7,481 Other long-term assets: Mutual funds held in Rabbi Trust $ 540 $ — $ — $ 540 $ 465 $ — $ — $ 465 Liabilities Accrued and other current liabilities: Rusnano payment derivative $ — $ — $ 2,000 $ 2,000 $ — $ — $ 2,000 $ 2,000

Balance sheet components (Table

Balance sheet components (Tables)	3 Months Ended
	Mar. 31, 2019
Balance Sheet Related Disclosures [Abstract]
Accounts receivable, Net	Accounts receivable, net, consists of the following (in thousands): March 31, 2019 December 31, 2018 Accounts receivable $ 63,717 $ 74,343 Trade notes receivable 1,757 672 Allowance for doubtful accounts (264 ) (264 ) $ 65,210 $ 74,751
Inventories, net	Inventories, net consist of the following (in thousands): March 31, 2019 December 31, 2018 Raw materials $ 24,727 $ 27,806 Work in process 15,240 13,044 Finished goods (1) 13,651 11,309 $ 53,618 $ 52,159 ________________________________________________________ (1) Finished goods inventory at customer vendor managed inventory locations was $5.5 million and $5.6 million as of March 31, 2019 and December 31, 2018 , respectively.
Prepaid expenses and other current assets	Prepaid expenses and other current assets consist of the following (in thousands): March 31, 2019 December 31, 2018 Prepaid taxes and taxes receivable $ 4,117 $ 5,461 Transition services agreement receivable (see Note 6) 12,263 11,999 Deposits and other prepaid expenses 2,913 3,020 Other receivable 4,702 6,125 $ 23,995 $ 26,605
Purchased intangible assets	Purchased intangible assets consist of the following (in thousands): March 31, 2019 December 31, 2018 Gross Assets Accumulated Amortization Net Assets Gross Accumulated Net Technology and patents $ 37,314 $ (35,457 ) $ 1,857 $ 37,029 $ (34,995 ) $ 2,034 Customer relationships 15,269 (15,269 ) — 15,146 (15,026 ) 120 Leasehold interest 1,269 (390 ) 879 1,238 (374 ) 864 $ 53,852 $ (51,116 ) $ 2,736 $ 53,413 $ (50,395 ) $ 3,018
Amortization expense of purchased intangible assets	The following table presents details of the amortization expense of the Company’s purchased intangible assets as reported in the condensed consolidated statements of operations (in thousands): Three Months Ended 2019 2018 Cost of goods sold $ 184 $ 203 Operating expenses 119 119 Total $ 303 $ 322
Estimated future amortization expense of purchased intangible assets	The estimated future amortization expense of purchased intangible assets as of March 31, 2019 , is as follows (in thousands): 2019 (remaining nine months) $ 552 2020 738 2021 645 2022 29 2023 29 Thereafter 743 $ 2,736
Accrued and other current liabilities	Accrued and other current liabilities consist of the following (in thousands): March 31, 2019 December 31, 2018 Transition services agreement payables (see Note 6) $ 11,776 $ 11,769 Employee-related 17,504 14,899 Asset sale related contingent liabilities (see Note 6) 6,918 6,751 Operating lease liabilities, current 2,274 — Accrued warranty 739 672 Deferred revenue, current 481 1,114 Income and other taxes payable 1,055 1,580 Rusnano payment derivative 2,000 2,000 Accrued litigation settlement 1,150 2,645 Other accrued expenses 6,372 8,858 $ 50,269 $ 50,288
Warranty accrual	The table below summarizes the movement in the warranty accrual, which is included in accrued and other current liabilities (in thousands): Three Months Ended 2019 2018 Beginning balance $ 672 $ 1,334 Warranty accruals 315 546 Settlements (248 ) (181 ) Ending balance $ 739 $ 1,699
Other noncurrent liabilities	Other noncurrent liabilities consist of the following (in thousands): March 31, 2019 December 31, 2018 Pension and other employee-related $ 4,573 $ 4,529 Deferred rent — 3,058 Government grant 1,993 2,108 Capital lease obligation — 282 Asset retirement obligations and other 3,556 3,522 $ 10,122 $ 13,499

Restructuring (Tables)

Restructuring (Tables)	3 Months Ended
	Mar. 31, 2019
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	Restructuring activities for the three months ended March 31, 2019 were as follows (in thousands): Employee Severance Facilities Consolidation Others Total Restructuring obligations December 31, 2018 $ 436 $ 769 $ 1,611 $ 2,816 Charges 14 — 165 179 Cash payments (450 ) (47 ) (17 ) (514 ) Adoption of ASC 842 — (620 ) — (620 ) Restructuring obligations March 31, 2019 $ — $ 102 $ 1,759 $ 1,861

Debt (Tables)

Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Carrying Amount and Weighted Average Interest Rate of the Company's Debt	The table below summarizes the carrying amount and weighted average interest rate of the Company’s debt (in thousands, except percentages): March 31, 2019 December 31, 2018 Carrying Amount Interest Rate Carrying Interest Notes payable to suppliers $ 2,339 — $ 4,795 Total notes payable and short-term borrowing $ 2,339 $ 4,795 Long-term debt, current and non-current: Borrowing under Wells Fargo Credit Facility $ 36,306 4.74 % $ 35,961 4.41 % Mitsubishi Bank loans 10,523 1.05% -1.45% 11,094 1.05% -1.45% Mitsubishi Bank and Yamanashi Chou Bank loan 6,572 1.1 % 6,898 1.1 % Finance lease liability 330 — Unaccreted discount and issuance costs (555 ) (602 ) Total long-term debt, net of unaccreted discount and issuance costs $ 53,176 $ 53,351 Reported as: Current portion of long-term debt $ 2,963 $ 2,897 Long-term debt, net of current portion 50,213 50,454 Total long-term debt, net of unaccreted discount and issuance costs $ 53,176 $ 53,351
Maturities of Long-term Debt	As of March 31, 2019 , maturities of total long-term debt were as follows (in thousands): 2019 (remaining nine months) $ 2,338 2020 3,122 2021 3,129 2022 39,425 2023 3,034 Thereafter 2,683 $ 53,731

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Lease, Cost	The components of lease expense were as follows (in thousands): Three Months Ended 2019 Operating lease cost $ 754 Variable and short-term lease cost 348 Total lease cost $ 1,102 Other information related to leases was as follows (in thousands, except lease term and discount rate): Three Months Ended 2019 Supplemental cash flow information Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases $ 835 Weighted average remaining lease term Operating leases 7.9 years Weighted average discount rate Operating leases 6.4 %
Lessee, Operating Lease, Liability, Maturity	Future minimum lease payments under non-cancellable leases as of March 31, 2019 were as follows (in thousands): Operating Leases 2019 (excluding the three months ended March 31, 2019) $ 2,773 2020 3,129 2021 3,074 2022 3,065 2023 3,014 Thereafter 11,194 Total future minimum lease payments 26,249 Less imputed interest (5,956 ) Total $ 20,293
Leasee, Balance Sheet Information	Reported as of March 31, 2019: Operating Leases Accrued and other current liabilities $ 2,274 Operating lease liabilities, noncurrent 18,019 Total $ 20,293
Schedule of Future Minimum Rental Payments for Operating Leases	As of December 31, 2018, the future minimum commitments under the Company’s non-cancelable operating leases and capital leases are as follows (in thousands): Operating Leases 2019 $ 3,618 2020 3,113 2021 3,059 2022 3,056 2023 3,049 Thereafter 11,437 Total future minimum lease payments $ 27,332

Stockholders' equity (Tables)

Stockholders' equity (Tables)	3 Months Ended
	Mar. 31, 2019
Stockholders' Equity Note [Abstract]
Schedule of Accumulated Other Comprehensive Income, Net of Related Taxes	The components of accumulated other comprehensive income (loss), net of related taxes, were as follows (in thousands): Foreign Currency Translation Adjustments Defined Benefit Pension Plan Adjustment Total Accumulated Other Comprehensive Income (loss) Balance as of December 31, 2018 $ (6,897 ) $ (229 ) $ (7,126 ) Other comprehensive income (loss), net of taxes of zero and reclassifications 2,937 — 2,937 Balance as of March 31, 2019 $ (3,960 ) $ (229 ) $ (4,189 )

Stock-based compensation (Table

Stock-based compensation (Tables)	3 Months Ended
	Mar. 31, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock Based Compensation Expense	The following table summarizes the stock-based compensation expense recognized in the three months ended March 31, 2019 and 2018 (in thousands): Three Months Ended 2019 2018 Cost of goods sold $ 601 $ 650 Research and development 881 773 Sales and marketing 678 938 General and administrative 1,178 986 $ 3,338 $ 3,347
Schedule of Share-based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions	The Company estimated the fair value of certain stock-based awards using a Black-Scholes-Merton valuation model with the following assumptions: Three Months Ended Stock options 2019 2018 Weighted-average expected term (years) — 6.00 Weighted-average volatility — 65% Risk-free interest rate — 2.27% Expected dividends — —% Stock appreciation units Weighted-average expected term (years) 1.67 2.10 Weighted-average volatility 64% 67% Risk-free interest rate 2.45%-2.63% 1.03% - 1.98% Expected dividends —% —% ESPP Weighted-average expected term (years) 0.73 0.73 Weighted-average volatility 61% 61% Risk-free interest rate 2.36% - 2.59% 1.20% - 1.31% Expected dividends —% —%
Estimated Fair Value of Certain Stock-Based Awards Using Black-Scholes-Merton Valuation Model	The fair value of market-based RSUs was measured on the grant date using Monte Carlo simulation model with the following assumptions: Year Ended Market-based restricted stock units 2018 Weighted-average volatility 66% Risk-free interest rate 2.79% Expected dividends —%
Summary of Stock Option and Restricted Stock Unit Activity	The following table summarizes the Company’s stock option and RSU activity, excluding market-based RSUs, during the three months ended March 31, 2019: Stock Options Restricted Stock Units Number of Shares Weighted Average Exercise Price Number of Weighted Balance as of December 31, 2018 3,202,745 $ 5.73 2,486,028 $ 7.87 Granted — — 33,598 7.10 Exercised/Converted (47,730 ) 3.50 (41,627 ) 7.88 Cancelled/Forfeited (9,688 ) 11.53 (59,100 ) 8.13 Balance as of March 31, 2019 3,145,327 5.75 2,418,899 7.85

Income taxes (Tables)

Income taxes (Tables)	3 Months Ended
	Mar. 31, 2019
Income Tax Disclosure [Abstract]
Summary of Income Tax (Provisions) Benefits	The provision for income taxes in the periods presented is based upon the income (loss) before income taxes (in thousands): Three Months Ended 2019 2018 Provision for income taxes $ (170 ) $ (638 )

Basis of presentation and sig_3

Basis of presentation and significant accounting policies - Narrative (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 01, 2019	Sep. 30, 2017
Concentration Risk [Line Items]
Working capital	$ 111,400,000
Cash, cash equivalents, short-term investments and restricted cash	78,900,000
Operating losses	11,929,000	$ 16,644,000
Net cash from operating activities	8,699,000	$ (3,456,000)
Accumulated deficit	411,563,000		$ 397,472,000
Short-term debt	2,339,000		4,795,000
Current portion of long-term debt	2,963,000		$ 2,897,000
Operating lease right-of-use assets	16,847,000			$ 17,300,000
Operating lease liability	$ 20,293,000			$ 20,800,000
Huawei Technologies | Revenue
Concentration Risk [Line Items]
Percentage of concentration of credit risk	49.00%	48.00%
Customer One | Revenue
Concentration Risk [Line Items]
Percentage of concentration of credit risk	24.00%	19.00%
Customer One | Accounts receivable
Concentration Risk [Line Items]
Percentage of concentration of credit risk	39.00%		35.00%
Top Five Customers | Revenue
Concentration Risk [Line Items]
Percentage of concentration of credit risk	87.00%	84.00%
Customer Two | Accounts receivable
Concentration Risk [Line Items]
Percentage of concentration of credit risk	17.00%		17.00%
Customer three | Accounts receivable
Concentration Risk [Line Items]
Percentage of concentration of credit risk	10.00%
Wells Fargo Bank, National Association | Revolving Credit Facility
Concentration Risk [Line Items]
Credit facility, maximum borrowing amount					$ 50,000,000
Wells Fargo Credit Facility | Line of Credit
Concentration Risk [Line Items]
Credit facility, maximum borrowing amount					$ 50,000,000
Line of credit fair value outstanding	$ 36,300,000
Unused part of credit facility	13,700,000
Minimum required unused borrowing capacity	$ 5,000,000

Revenue - Revenue by Product Gr

Revenue - Revenue by Product Group (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 79,366	$ 68,586
High Speed Products
Disaggregation of Revenue [Line Items]
Total revenue	70,168	59,090
Network Products and Solutions
Disaggregation of Revenue [Line Items]
Total revenue	$ 9,198	$ 9,496

Revenue - Revenue From External

Revenue - Revenue From External Customers By Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Disaggregation of Revenue [Line Items]
Total revenue	$ 79,366	$ 68,586
China
Disaggregation of Revenue [Line Items]
Total revenue	45,547	41,672
Americas
Disaggregation of Revenue [Line Items]
Total revenue	13,829	12,208
Rest of world
Disaggregation of Revenue [Line Items]
Total revenue	$ 19,990	$ 14,706

Revenue - Narrative (Details)

Revenue - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Revenue from Contract with Customer [Abstract]
Contract with customer, liability, revenue recognized	$ 0.6	$ 0.4

Net loss per share - Computatio

Net loss per share - Computation of Basic and Diluted Net Income (Loss) per Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Numerator:
Net loss	$ (14,091)	$ (18,246)
Weighted average shares used to compute per share amount:
Basic (in shares)	46,414	44,259
Diluted (in shares)	46,414	44,259
Basic net loss per share (USD per share)	$ (0.30)	$ (0.41)
Diluted net loss per share (USD per share)	$ (0.30)	$ (0.41)

Net loss per share - Potentiall

Net loss per share - Potentially Dilutive Securities Excluded From Computation of Diluted Net Loss per Share Attributable to Common Stockholders (Details) - shares shares in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share (in shares)	6,655	6,728
Employee stock options
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share (in shares)	3,145	3,940
Restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share (in shares)	2,419	2,377
Market-based restricted stock units
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share (in shares)	677	0
Employee stock purchase plan
Antidilutive Securities Excluded From Computation Of Earnings Per Share
Potentially dilutive securities, excluded from computation of diluted net income (loss) per share (in shares)	414	411

Cash, cash equivalents, short_3

Cash, cash equivalents, short-term investments and restricted cash - Short term investments and restricted cash and investments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Cash and cash equivalents:
Cash	$ 59,793	$ 58,185
Cash equivalents	0	0
Cash and cash equivalents	59,793	58,185
Short-term investments	7,524	7,481
Restricted cash	11,577	11,053
Total cash, cash equivalents and restricted cash shown in the statement of cash flows	$ 71,370	$ 69,238	$ 74,589	$ 81,564

Cash, cash equivalents, short_4

Cash, cash equivalents, short-term investments and restricted cash - Summary of unrealized gains and losses (Details)	3 Months Ended
	Mar. 31, 2019USD ($)investment	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)
Debt Securities, Available-for-sale [Line Items]
Impairment losses on marketable securities	$ 0	$ 0
Number of marketable securities in an unrealized loss position | investment	0
Money market funds
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 7,524,000		$ 7,481,000
Gross Unrealized Gains	0		0
Gross Unrealized Loss	0		0
Fair Value	7,524,000		7,481,000
Short-term investments
Debt Securities, Available-for-sale [Line Items]
Fair Value	$ 7,524,000		$ 7,481,000

Fair value disclosures - Assets

Fair value disclosures - Assets and liabilities measured at fair value on recurring basis (Details) - USD ($)	Mar. 31, 2019	Dec. 31, 2018
Fair Value, Measurements, Recurring | Rusnano payment derivative
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	$ 2,000,000	$ 2,000,000
Fair Value, Measurements, Recurring | Rusnano payment derivative | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Recurring | Rusnano payment derivative | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Recurring | Rusnano payment derivative | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	2,000,000	2,000,000
Fair Value, Measurements, Recurring | Money market funds
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	7,524,000	7,481,000
Fair Value, Measurements, Recurring | Money market funds | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	7,524,000	7,481,000
Fair Value, Measurements, Recurring | Money market funds | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Recurring | Money market funds | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Recurring | Mutual funds held in Rabbi Trust
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	540,000	465,000
Fair Value, Measurements, Recurring | Mutual funds held in Rabbi Trust | Level 1
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	540,000	465,000
Fair Value, Measurements, Recurring | Mutual funds held in Rabbi Trust | Level 2
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Recurring | Mutual funds held in Rabbi Trust | Level 3
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	0	0
Fair Value, Measurements, Nonrecurring
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fair value, net asset (liability)	$ 0	$ 0

Asset sale (Details)

Asset sale (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jan. 31, 2017	Dec. 31, 2017	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Transition services agreement receivable (Note 5)			$ 12,263	$ 11,999
Transition services agreement payables (see Note 6)			11,776	11,769
Assets held for sale			3,074	$ 2,971
Gain within operating income		$ 2,200
Other current liabilities | Indemnification agreement
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Asset sale related contingent liabilities (see Note 6)			$ 6,900
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale					$ 13,900
Reclassification from assets held-for-sale	$ 3,400
Assets sold	12,800
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Inventories
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, other					13,100
Assets sold	12,100
Low Speed Transceiver Products | Disposal Group, Disposed of by Sale, Not Discontinued Operations | Property, plant and equipment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale, other					$ 800
Assets sold	700
Low Speed Transceiver Products | APAT OE | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Consideration received pursuant to asset purchase agreement	25,000
Proceeds from post-closing transaction services fees under transition services agreement	1,400
Disposal group consideration adjustment	21,600
Consideration adjustment for potential indemnification claims	$ 10,000

Balance sheet components - Acco

Balance sheet components - Accounts receivable, net (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Accounts receivable	$ 63,717	$ 74,343
Trade notes receivable	1,757	672
Allowance for doubtful accounts	(264)	(264)
Account and trade note receivables, net	$ 65,210	$ 74,751

Balance sheet components - Inve

Balance sheet components - Inventories and Held for Sale (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Long Lived Assets Held-for-sale [Line Items]
Raw materials	$ 27,806	$ 24,727		$ 27,806
Work in process	13,044	15,240		13,044
Finished goods	11,309	13,651		11,309
Inventories	52,159	53,618		52,159
Finished goods, at vendor managed inventory locations	5,600	5,500		5,600
Restructuring charges		179	$ 31
Assets held for sale	2,971	3,074		2,971
Property, plant and equipment
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		2,600
Prepaid Expenses and Other Current Assets
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale		$ 500
Rusnano Group
Long Lived Assets Held-for-sale [Line Items]
Restructuring charges				1,600
Rusnano Group | Derivative
Long Lived Assets Held-for-sale [Line Items]
Accrued payments	$ 2,000			$ 2,000
NeoPhotonics Corporation | Joint Stock Company Rusnano
Long Lived Assets Held-for-sale [Line Items]
Assets held for sale, percent of component acquired	100.00%

Balance sheet components - Prep

Balance sheet components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Prepaid taxes and taxes receivable	$ 4,117		$ 5,461
Transition services agreement receivable (see Note 6)	12,263		11,999
Deposits and other prepaid expenses	2,913		3,020
Other receivable	4,702		6,125
Prepaid expenses and other current assets	23,995		$ 26,605
Capital expenditures incurred but not yet paid	$ 1,800	$ 3,500

Balance sheet components - Purc

Balance sheet components - Purchased intangible assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Finite-Lived Intangible Assets [Line Items]
Gross Assets	$ 53,852	$ 53,413
Accumulated Amortization	(51,116)	(50,395)
Net Assets	2,736	3,018
Technology and patents
Finite-Lived Intangible Assets [Line Items]
Gross Assets	37,314	37,029
Accumulated Amortization	(35,457)	(34,995)
Net Assets	1,857	2,034
Customer relationships
Finite-Lived Intangible Assets [Line Items]
Gross Assets	15,269	15,146
Accumulated Amortization	(15,269)	(15,026)
Net Assets	0	120
Leasehold interest
Finite-Lived Intangible Assets [Line Items]
Gross Assets	1,269	1,238
Accumulated Amortization	(390)	(374)
Net Assets	$ 879	$ 864

Balance sheet components - Amor

Balance sheet components - Amortization expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Cost of goods sold	$ 184	$ 203
Operating expenses	119	119
Total	$ 303	$ 322

Balance sheet components - Esti

Balance sheet components - Estimated future amortization expense of purchased intangible assets (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
2019 (remaining nine months)	$ 552
2020	738
2021	645
2022	29
2023	29
Thereafter	743
Net Assets	$ 2,736	$ 3,018

Balance sheet components - Accr

Balance sheet components - Accrued and other current liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Transition services agreement payables (see Note 6)	$ 11,776	$ 11,769
Employee-related	17,504	14,899
Asset sale related contingent liabilities (see Note 6)	6,918	6,751
Operating lease liabilities, current	2,274
Accrued warranty	739	672	$ 1,699	$ 1,334
Deferred revenue, current	481	1,114
Income and other taxes payable	1,055	1,580
Rusnano payment derivative	2,000	2,000
Accrued litigation settlement	1,150	2,645
Other accrued expenses	6,372	8,858
Accrued and other current liabilities	$ 50,269	$ 50,288

Balance sheet components - Warr

Balance sheet components - Warranty accrual (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Movement in Standard and Extended Product Warranty Accrual, Increase (Decrease) [Roll Forward]
Beginning balance	$ 672	$ 1,334
Warranty accruals	315	546
Settlements	(248)	(181)
Ending balance	$ 739	$ 1,699

Balance sheet components - Othe

Balance sheet components - Other noncurrent liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Balance Sheet Related Disclosures [Abstract]
Pension and other employee-related	$ 4,573	$ 4,529
Deferred rent		3,058
Government grant	1,993	2,108
Capital lease obligation		282
Asset retirement obligations and other	3,556	3,522
Other noncurrent liabilities	$ 10,122	$ 13,499

Restructuring - Narrative (Deta

Restructuring - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred	$ 179
Restructuring reserve recorded in accrued and other current liabilities	1,900
Operating Expense
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred	$ 200
Cost of Sales And Operating Expense
Restructuring Cost and Reserve [Line Items]
Restructuring charges incurred		$ 100

Restructuring - Reserve Rollfor

Restructuring - Reserve Rollforward (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Restructuring Reserve [Roll Forward]
Restructuring obligations December 31, 2018	$ 2,816
Charges	179
Cash payments	(514)
Adoption of ASC 842	(620)
Restructuring obligations March 31, 2019	1,861
Employee Severance
Restructuring Reserve [Roll Forward]
Restructuring obligations December 31, 2018	436
Charges	14
Cash payments	(450)
Adoption of ASC 842	0
Restructuring obligations March 31, 2019	0
Facilities Consolidation
Restructuring Reserve [Roll Forward]
Restructuring obligations December 31, 2018	769
Charges	0
Cash payments	(47)
Adoption of ASC 842	(620)
Restructuring obligations March 31, 2019	102
Others
Restructuring Reserve [Roll Forward]
Restructuring obligations December 31, 2018	1,611
Charges	165
Cash payments	(17)
Adoption of ASC 842	0
Restructuring obligations March 31, 2019	$ 1,759

Debt - Components of Debt Oblig

Debt - Components of Debt Obligations and Weighted Average Interest Rate (Details) $ in Thousands, ¥ in Millions	Mar. 31, 2019USD ($)	Mar. 31, 2019JPY (¥)	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Short-term debt	$ 2,339		$ 4,795
Finance lease liability	330
Unaccreted discount and issuance costs	(555)		(602)
Total long-term debt, net of unaccreted discount and issuance costs	53,176		53,351
Current portion of long-term debt	2,963		2,897
Long-term debt, net of current portion	50,213		50,454
Line of Credit | Wells Fargo Credit Facility
Debt Instrument [Line Items]
Long-term debt, gross	$ 36,306		$ 35,961
Weighted average interest rate	4.74%	4.74%	4.41%
Line of Credit | Mitsubishi Bank Loans | Minimum
Debt Instrument [Line Items]
Weighted average interest rate	1.05%	1.05%	1.05%
Line of Credit | Mitsubishi Bank Loans | Maximum
Debt Instrument [Line Items]
Weighted average interest rate	1.45%	1.45%	1.45%
Notes Payable to Banks | Mitsubishi Bank Loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 10,523		$ 11,094
Total long-term debt, net of unaccreted discount and issuance costs | ¥		¥ 591.7
Notes Payable to Banks | Mitsubishi Bank Loans And Yamanashi Chou Bank Loans
Debt Instrument [Line Items]
Long-term debt, gross	$ 6,572		$ 6,898
Weighted average interest rate	1.10%	1.10%	1.10%
Notes payable to suppliers | Loans With Suppliers
Debt Instrument [Line Items]
Short-term debt	$ 2,339		$ 4,795

Debt - Notes Payable (Details)

Debt - Notes Payable (Details)	1 Months Ended						3 Months Ended
	Aug. 31, 2018USD ($)	May 31, 2018USD ($)	Feb. 28, 2018USD ($)	Jan. 31, 2018USD ($)	Nov. 30, 2017USD ($)	Jul. 31, 2017USD ($)	Mar. 31, 2019CNY (¥)line_of_credit	Mar. 31, 2019USD ($)line_of_credit	Dec. 31, 2018USD ($)
Debt Instrument [Line Items]
Short-term debt								$ 2,339,000	$ 4,795,000
Notes payable to suppliers | Loans With Suppliers
Debt Instrument [Line Items]
Short-term debt								2,339,000	4,795,000
Notes payable to suppliers | Loans With Suppliers | Minimum
Debt Instrument [Line Items]
Debt instrument, term							3 months
Notes payable to suppliers | Loans With Suppliers | Maximum
Debt Instrument [Line Items]
Debt instrument, term							6 months
Loans Payable | First Credit Facility
Debt Instrument [Line Items]
Current borrowing capacity							¥ 120,000,000	17,900,000
Loans Payable | Second Line of Credit
Debt Instrument [Line Items]
Current borrowing capacity							30,000,000	4,500,000
Bankers Acceptance
Debt Instrument [Line Items]
Restricted cash and investments, current								2,600,000	2,600,000
Bankers Acceptance | First Credit Facility
Debt Instrument [Line Items]
Current borrowing capacity							¥ 240,000,000	35,800,000
Percentage of compensating balance requirement for bank acceptance drafts							50.00%
Bankers Acceptance | Second Line of Credit
Debt Instrument [Line Items]
Percentage of compensating balance requirement for bank acceptance drafts							50.00%
Bankers Acceptance | Loans With Suppliers
Debt Instrument [Line Items]
Short-term debt								2,300,000	$ 4,800,000
Short Term Loans | Second Line of Credit
Debt Instrument [Line Items]
Current borrowing capacity							¥ 60,000,000	$ 8,900,000
Notes Payable to Banks | Notes Payable CITIC Bank
Debt Instrument [Line Items]
Proceeds from lines of credit			$ 17,000,000			$ 17,000,000
Debt instrument, interest rate, stated percentage			4.70%
Repayments of lines of credit	$ 17,000,000
Debt instrument, basis spread						2.55%
China | Notes payable to suppliers | First Credit Facility
Debt Instrument [Line Items]
Proceeds from lines of credit					$ 17,000,000
Repayments of lines of credit		$ 17,000,000
China | Bankers Acceptance | First Credit Facility
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage					4.10%
China | Notes Payable to Banks | Notes Payable CITIC Bank
Debt Instrument [Line Items]
Repayments of lines of credit				$ 17,000,000
Line of Credit | China
Debt Instrument [Line Items]
Number of debt instruments | line_of_credit							2	2
CITIC Bank | Line of Credit | China
Debt Instrument [Line Items]
Credit facility, maximum borrowing amount							¥ 250,000,000	$ 37,200,000
CITIC Bank | Bank Acceptance Drafts | China
Debt Instrument [Line Items]
Percentage of compensating balance requirement for bank acceptance drafts							36.00%
Credit facility, maximum borrowing amount							¥ 390,600,000	$ 58,200,000

Debt - Credit Facilities (Detai

Debt - Credit Facilities (Details) - USD ($)	1 Months Ended			3 Months Ended
	Apr. 30, 2019	Jan. 31, 2019	Sep. 30, 2017	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Line of Credit Facility [Line Items]
Repayment of notes payable				$ 2,559,000	$ 868,000
Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Repayments of lines of credit		$ 5,000,000
Line of Credit | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Credit facility, maximum borrowing amount			$ 50,000,000
Cash balance for borrowing			100.00%
Cash balance max borrowing			$ 15,000,000
Line of credit facility increase			25,000,000
Line of credit facility, outstanding			30,000,000
Repayment of notes payable			20,000,000
Line of credit facility, maximum indebtedness under debt covenant			20,000,000
Unused borrowing capacity			$ 5,000,000
Line of credit fair value outstanding				$ 36,300,000
Weighted average interest rate				4.74%		4.41%
Unused part of credit facility				$ 13,700,000
Minimum required unused borrowing capacity				$ 5,000,000
Line of Credit | Libor Plus Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Weighted average interest rate				4.74%
Line of Credit | Prime Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Commitment fee			0.25%
Line of Credit | Minimum | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Revolver accounts receivable			80.00%
Line of Credit | Minimum | Libor Plus Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, basis spread			1.50%
Line of Credit | Minimum | Prime Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, basis spread			0.50%
Line of Credit | Maximum | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Revolver accounts receivable			85.00%
Line of Credit | Maximum | Libor Plus Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, basis spread			1.75%
Line of Credit | Maximum | Prime Rate | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Debt instrument, basis spread			0.75%
Subsequent Event | Wells Fargo Credit Facility
Line of Credit Facility [Line Items]
Repayments of lines of credit	$ 5,000,000

Debt - Mitsubishi Bank Loans (D

Debt - Mitsubishi Bank Loans (Details) $ in Thousands	Feb. 25, 2015USD ($)	Feb. 25, 2015JPY (¥)	Jan. 31, 2018USD ($)	Jan. 31, 2018JPY (¥)	Mar. 31, 2017USD ($)	Mar. 31, 2019USD ($)	Mar. 31, 2019JPY (¥)	Dec. 31, 2018USD ($)	Mar. 31, 2017JPY (¥)	Feb. 25, 2015JPY (¥)
Debt Instrument [Line Items]
Long-term debt | $						$ 53,176		$ 53,351
Notes Payable to Banks | Mitsubishi Bank Term Loan A
Debt Instrument [Line Items]
Debt, aggregate principal amount	$ 4,400									¥ 500,000,000
Notes Payable to Banks | Mitsubishi Bank Term Loan B
Debt Instrument [Line Items]
Debt, aggregate principal amount	$ 9,000									¥ 1,000,000,000
Debt, periodic principal payments		¥ 8,333,000
Debt, lump sum payment on the maturity date		¥ 8,373,000
Long-term debt | $						5,300
Notes Payable to Banks | Mitsubishi Bank Term Loan B | Tokyo interbank offer rate
Debt Instrument [Line Items]
Debt instrument, basis spread	1.40%	1.40%
Notes Payable to Banks | Mitsubishi Bank Loans
Debt Instrument [Line Items]
Loan structuring fee including consumption tax	$ 400	¥ 40,500,000
Long-term debt							¥ 591,700,000
Unamortized debt issuance costs						$ 600	¥ 61,500,000
Notes Payable to Banks | Mitsubishi Bank Loans | Tokyo interbank offer rate
Debt Instrument [Line Items]
Debt instrument, basis spread	1.40%	1.40%
Notes Payable to Banks | 2017 Mitsubishi Bank Loan
Debt Instrument [Line Items]
Debt, aggregate principal amount					$ 6,200				¥ 690,000,000
Debt instrument, term					72 months
Line of credit facility, outstanding					$ 6,200				¥ 690,000,000
Notes Payable to Banks | 2017 Mitsubishi Bank Loan | Tokyo interbank offer rate
Debt Instrument [Line Items]
Debt instrument, basis spread					1.00%
Mitsubishi Bank | Mitsubishi Bank Term Loan A
Debt Instrument [Line Items]
Repayments of lines of credit			$ 4,400	¥ 500,000,000

Debt - Mitsubishi Bank and Yama

Debt - Mitsubishi Bank and Yamanashi Chou Bank Loans (Details) - 1 months ended Jan. 31, 2018 - Mitsubishi Bank and The Yamanashi Chou Bank, Ltd. - Term Loan C $ in Millions	USD ($)	JPY (¥)
Debt Instrument [Line Items]
Credit facility, maximum borrowing amount	$ 7.7	¥ 850,000,000
Debt instrument, term	82 months
Tokyo interbank offer rate
Debt Instrument [Line Items]
Debt instrument, basis spread	1.00%

Debt - Maturities of Long-Term

Debt - Maturities of Long-Term debt (Details) $ in Thousands	Mar. 31, 2019USD ($)
Debt Disclosure [Abstract]
2019 (remaining nine months)	$ 2,338
2020	3,122
2021	3,129
2022	39,425
2023	3,034
Thereafter	2,683
Total long-term debt, current and non-current	$ 53,731

Leases - Narrative (Details)

Leases - Narrative (Details)	3 Months Ended
	Mar. 31, 2019
Lessee, Lease, Description [Line Items]
Termination period	1 year
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease term	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease term	9 years

Leases - Lease Cost (Details)

Leases - Lease Cost (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating lease cost	$ 754
Variable and short-term lease cost	348
Total lease cost	$ 1,102

Leases - Cash Flows (Details)

Leases - Cash Flows (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Operating cash flows from operating leases	$ 835
Weighted average remaining lease term, Operating leases	7 years 10 months 24 days
Weighted average discount rate, Operating leases	6.40%

Leases - Leases, Liability, Mat

Leases - Leases, Liability, Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Operating Lease Liabilities, Payments Due [Abstract]
2019 (excluding the three months ended March 31, 2019)	$ 2,773
2020	3,129
2021	3,074
2022	3,065
2023	3,014
Thereafter	11,194
Total future minimum lease payments	26,249
Less imputed interest	(5,956)
Total	$ 20,293	$ 20,800

Leases - Balance Sheet Informat

Leases - Balance Sheet Information (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019
Leases [Abstract]
Operating Leases, Accrued and other current liabilities	$ 2,274
Operating Leases, Operating lease liabilities, noncurrent	18,019
Operating Leases, Total	$ 20,293	$ 20,800

Leases - Minimum Lease Payments

Leases - Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2018USD ($)
Operating Leases
2019	$ 3,618
2020	3,113
2021	3,059
2022	3,056
2023	3,049
Thereafter	11,437
Total future minimum lease payments	$ 27,332

Japan pension plan (Details)

Japan pension plan (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Retirement Benefits [Abstract]
Pension liability	$ 4	$ 4.3
Pension liability included in accrued and other current liabilities		$ 0.3

Commitments and Contingencies (

Commitments and Contingencies (Details) ¥ in Thousands

Oct. 25, 2017CNY (¥)

Oct. 25, 2017USD ($)

Jun. 16, 2017USD ($)

Dec. 27, 2016USD ($)

Jun. 30, 2019USD ($)

Feb. 28, 2019CNY (¥)

Feb. 28, 2019USD ($)

Jan. 31, 2019USD ($)

Dec. 31, 2018CNY (¥)lawsuit

Dec. 31, 2018USD ($)lawsuit

Nov. 30, 2018CNY (¥)

Nov. 30, 2018USD ($)

Sep. 30, 2018USD ($)

Jul. 31, 2018USD ($)

Apr. 30, 2018USD ($)

Nov. 30, 2016lawsuit

Mar. 31, 2019USD ($)

Dec. 31, 2010lawsuitclaim

Dec. 31, 2019USD ($)

Dec. 31, 2015USD ($)

Dec. 31, 2012USD ($)

Commitments And Contingencies Disclosure [Line Items]

Number of defendants | lawsuit

4

Penalty payment derivative

$ 2,000,000

$ 2,000,000

Russian federation | Scenario, Forecast

Commitments And Contingencies Disclosure [Line Items]

Exit fees for future

$ 2,000,000

Embedded derivative financial instruments | Maximum

Commitments And Contingencies Disclosure [Line Items]

Other non-current liability

$ 5,000,000

Indemnification agreement

Commitments And Contingencies Disclosure [Line Items]

Payment for legal settlement

0

Performance guarantee | Private Placement

Commitments And Contingencies Disclosure [Line Items]

Other non-current liability

6,500,000

$ 30,000,000

Rusnano Group | Disposal Group, Not Discontinued Operations | NeoPhotonics Corporation, LLC

Commitments And Contingencies Disclosure [Line Items]

Ownership to be disposed

100.00%

Consideration received pursuant to asset purchase agreement

$ 3,000,000

Penalty payment cancellation

$ 1,000,000

Oyster Communications, Inc.

Commitments And Contingencies Disclosure [Line Items]

New claims filed, number | lawsuit

9

Finisar Corp

Commitments And Contingencies Disclosure [Line Items]

Pending claims | claim

2

Lestina International Ltd. litigation

Commitments And Contingencies Disclosure [Line Items]

Damages sought, value

$ 3,000,000

Lawsuit Filed By Lestina International Ltd. | NeoPhotonics Dongguan Co., Ltd | Lestina International Ltd.

Commitments And Contingencies Disclosure [Line Items]

Loss contingency, damages awarded, value

$ 2,200,000

2,200,000

Damages paid

$ 1,200,000

Lawsuit Filed By Lestina International Ltd. | NeoPhotonics Dongguan Co., Ltd | Lestina International Ltd. | Scenario, Forecast

Commitments And Contingencies Disclosure [Line Items]

Damages paid

$ 1,000,000

APAT Arbitration

Commitments And Contingencies Disclosure [Line Items]

Damages sought, value

$ 1,500,000

7,100,000

$ 7,800,000

$ 12,000,000

Damages awarded to company

¥ 700

$ 110,000

Attorney fees

¥ 810

$ 121,000

APAT OE Legal Dispute

Commitments And Contingencies Disclosure [Line Items]

Damages sought, value

$ 20,000,000

APAT OE Legal Dispute | APAT OE

Commitments And Contingencies Disclosure [Line Items]

New claims filed, number | lawsuit

2

2

APAT OE And NeoChina

Commitments And Contingencies Disclosure [Line Items]

Damages sought, value

¥ 50,900

$ 7,600,000

Assets ordered to be preserved

$ 29,000,000

Claim Against APAT OE And Zheijiang Merchants Property Insurance Company | NeoChina

Commitments And Contingencies Disclosure [Line Items]

Damages sought, value

¥ 350

$ 52,000

Cisco Settlement Agreement

Commitments And Contingencies Disclosure [Line Items]

Loss contingency, damages awarded, value

$ 150,000

$ 300,000

Stockholders' equity - Narrativ

Stockholders' equity - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Mar. 31, 2019
Class of Stock [Line Items]
Accumulated deficit subject to restriction	$ 9
Minimum
Class of Stock [Line Items]
Accumulated profits	10.00%
Employee stock options
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)		9,032,639
Employee stock purchase plan
Class of Stock [Line Items]
Common stock reserved for future issuance (in shares)		574,462

Stockholders' equity - Accumula

Stockholders' equity - Accumulated Other Comprehensive Income (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Stockholders' Equity Note [Abstract]
Other comprehensive income (loss), tax	$ 0
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	160,240,000	$ 194,451,000
Other comprehensive income (loss), net of taxes of zero and reclassifications	2,937,000	6,103,000
Ending balance	152,558,000	183,720,000
Foreign Currency Translation Adjustments
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(6,897,000)
Other comprehensive income (loss), net of taxes of zero and reclassifications	2,937,000
Ending balance	(3,960,000)
Defined Benefit Pension Plan Adjustment
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(229,000)
Other comprehensive income (loss), net of taxes of zero and reclassifications	0
Ending balance	(229,000)
Accumulated other comprehensive income (loss)
AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward]
Beginning balance	(7,126,000)	398,000
Ending balance	$ (4,189,000)	$ 6,501,000

Stock-based compensation - Summ

Stock-based compensation - Summary of stock-based compensation expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	$ 3,338	$ 3,347
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	601	650
Research and development
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	881	773
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	678	938
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Share-based compensation	$ 1,178	$ 986

Stock-based compensation - Valu

Stock-based compensation - Valuation assumptions of stock-based awards (Details)	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average expected term (years)		6 years
Weighted-average volatility	0.00%	65.00%
Risk-free interest rate	0.00%	2.27%
Expected dividends	0.00%	0.00%
Stock Appreciation Units (SAUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average expected term (years)	1 year 8 months 1 day	2 years 1 month 6 days
Weighted-average volatility	64.00%	67.00%
Risk-free interest rate minimum	2.45%	1.03%
Risk-free interest rate maximum	2.63%	1.98%
Expected dividends	0.00%	0.00%
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average expected term (years)	8 months 22 days	8 months 22 days
Weighted-average volatility	61.00%	61.00%
Risk-free interest rate minimum	2.36%	1.20%
Risk-free interest rate maximum	2.59%	1.31%
Expected dividends	0.00%	0.00%
Market-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average volatility			66.00%
Risk-free interest rate			2.79%
Expected dividends			0.00%

Stock-based compensation - Stoc

Stock-based compensation - Stock Options and RSUs (Details)	3 Months Ended
	Mar. 31, 2019$ / sharesshares
Employee stock options
Number of Shares
Beginning Balance (in shares) | shares	3,202,745
Granted (in shares) | shares	0
Exercised/Converted (in shares) | shares	(47,730)
Cancelled/Forfeited (in shares) | shares	(9,688)
Ending Balance (in shares) | shares	3,145,327
Weighted Average Exercise Price
Beginning Balance (in USD per share) | $ / shares	$ 5.73
Granted (in USD per share) | $ / shares	0
Exercised/Converted (in USD per share) | $ / shares	3.50
Cancelled/Forfeited (in USD per share) | $ / shares	11.53
Ending Balance (in USD per share) | $ / shares	$ 5.75
Restricted stock units
Number of Units
Beginning Balance (in shares) | shares	2,486,028
Granted (in shares) | shares	33,598
Exercised/Converted (in shares) | shares	(41,627)
Cancelled/Forfeited (in shares) | shares	(59,100)
Ending Balance (in shares) | shares	2,418,899
Weighted Average Exercise Price
Beginning Balance (in USD per share) | $ / shares	$ 7.87
Granted (in USD per share) | $ / shares	7.10
Exercised/Converted (in USD per share) | $ / shares	7.88
Cancelled/Forfeited (in USD per share) | $ / shares	8.13
Ending Balance (in USD per share) | $ / shares	$ 7.85

Stock-based compensation - Narr

Stock-based compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Employee stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 1.4
Compensation cost not yet recognized, period for recognition	1 year 7 months 6 days
Restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 11.1
Compensation cost not yet recognized, period for recognition	1 year 10 months 24 days
Awards granted in the period (in shares)	33,598
Shares vested (in shares)	41,627
Granted (in USD per share)	$ 7.10
Shares outstanding (in shares)	2,418,899		2,486,028
Market-based restricted stock units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Compensation cost not yet recognized, period for recognition	3 years 3 months 2 days
Awards granted in the period (in shares)			695,000
Shares vested (in shares)	0
Shares canceled (in shares)	17,500
Granted (in USD per share)	$ 5.82
Unrecognized share based compensation	$ 2.5
Stock Appreciation Units (SAUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted in the period (in shares)	0	0
Shares outstanding (in shares)	191,066		192,872
SAU-related liabilities	$ 0.6		$ 0.6
Employee stock purchase plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense	$ 0.4

Income taxes - Provision for in

Income taxes - Provision for income taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Tax Disclosure [Abstract]
Provision for income taxes	$ (170)	$ (638)

Income taxes - Additional infor

Income taxes - Additional information (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustments to accumulated deficit for new accounting pronouncements		$ (1,824)
Decrease to the amounts of uncertain tax positions previously determined	$ 0
Increase to the amounts of uncertain tax positions previously determined	$ 0
Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Adjustments to accumulated deficit for new accounting pronouncements		$ 1,800

Subsequent events (Details)

Subsequent events (Details) - Subsequent Event $ in Millions	1 Months Ended
	Apr. 30, 2019USD ($)
Disposed of by Sale | NeoPhotonics Corporation, LLC
Subsequent Event [Line Items]
Percent of ownership disposed	100.00%
Consideration received	$ 2
Exit fee settlements	2
Wells Fargo | Line of Credit
Subsequent Event [Line Items]
Repayments of lines of credit	$ 5

Uncategorized Items - nptn-2019

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ (1,824,000)