Calix (CALX) 10-Q 8 Nov 17 2017 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2017	Nov. 02, 2017
Document and Entity Information [Abstract]
Entity Registrant Name	CALIX, INC
Entity Central Index Key	1,406,666
Document Type	10-Q
Document Period End Date	Sep. 30, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q3
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		50,394,757

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 64,184	$ 50,359
Marketable securities	6,598	27,748
Accounts receivable, net	44,227	51,336
Inventory	36,321	44,545
Deferred cost of revenue	22,859	34,763
Prepaid expenses and other current assets	11,504	10,571
Total current assets	185,693	219,322
Property and equipment, net	16,997	17,984
Goodwill	116,175	116,175
Other assets	777	1,994
Total assets	319,642	355,475
Current liabilities:
Accounts payable	29,576	23,827
Accrued liabilities	59,401	69,715
Deferred revenue	28,228	27,854
Line of credit	30,000	0
Total current liabilities	147,205	121,396
Long-term portion of deferred revenue	21,173	20,237
Other long-term liabilities	881	878
Total liabilities	169,259	142,511
Commitments and contingencies (See Note 7)
Stockholders’ equity:
Preferred stock, $0.025 par value; 5,000 shares authorized; no shares issued and outstanding as of September 30, 2017 and December 31, 2016	0	0
Common stock, $0.025 par value; 100,000 shares authorized; 55,712 shares issued and 50,382 shares outstanding as of September 30, 2017, and 54,722 shares issued and 49,392 shares outstanding as of December 31, 2016	1,393	1,368
Additional paid-in capital	843,811	836,563
Accumulated other comprehensive loss	(344)	(656)
Accumulated deficit	(654,491)	(584,325)
Treasury stock, 5,330 shares as of September 30, 2017 and December 31, 2016	(39,986)	(39,986)
Total stockholders’ equity	150,383	212,964
Total liabilities and stockholders’ equity	$ 319,642	$ 355,475

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2017	Dec. 31, 2016
Statement of Financial Position [Abstract]
Preferred stock, par value (in dollars per share)	$ 0.025	$ 0.025
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.025	$ 0.025
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	55,712,000	54,722,000
Common stock, shares outstanding	50,382,000	49,392,000
Treasury stock, shares	5,330,000	5,330,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Revenue:
Products		$ 106,442	$ 114,029	$ 305,395	$ 305,853
Services		22,385	7,158	67,073	21,134
Total revenue		128,827	121,187	372,468	326,987
Cost of revenue:
Products	[1]	55,494	60,662	171,166	159,856
Services	[1]	28,700	6,981	78,969	18,099
Total cost of revenue		84,194	67,643	250,135	177,955
Gross profit		44,633	53,544	122,333	149,032
Operating expenses:
Research and development	[1]	32,633	28,119	99,391	75,925
Sales and marketing	[1]	18,448	20,575	59,306	58,850
General and administrative	[1]	10,203	8,615	30,161	32,940
Amortization of intangible assets		0	0	0	1,701
Restructuring charges		612	0	2,268	0
Litigation settlement gain		0	(4,500)	0	(4,500)
Total operating expenses		61,896	52,809	191,126	164,916
Income (loss) from operations		(17,263)	735	(68,793)	(15,884)
Interest and other income (expense), net:
Interest income (expense), net		(60)	80	88	274
Other income (expense), net		(305)	30	(386)	145
Income (loss) before provision for income taxes		(17,628)	845	(69,091)	(15,465)
Provision for income taxes		225	209	1,075	454
Net income (loss)		$ (17,853)	$ 636	$ (70,166)	$ (15,919)
Net income (loss) per common share:
Net income (loss) per common share, basic (in dollars per share)		$ (0.35)	$ 0.01	$ (1.40)	$ (0.33)
Net income (loss) per common share, diluted (in dollars per share)		$ (0.35)	$ 0.01	$ (1.40)	$ (0.33)
Weighted-average number of shares used to compute net loss per common share:
Basic (in shares)		50,336	48,773	49,960	48,578
Diluted (in shares)		50,336	49,309	49,960	48,578
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on available-for-sale marketable securities, net		$ 4	$ (9)	$ 3	$ 97
Foreign currency translation adjustments, net		116	(87)	309	(128)
Total other comprehensive income, net of tax		120	(96)	312	(31)
Comprehensive income (loss)		$ (17,733)	$ 540	$ (69,854)	$ (15,950)
[1]	Includes stock-based compensation as follows: Three and Nine Months Ended September 30, 2017 and September 24, 2016; Cost of revenue: Products - $137, $120, $349, $338 ; Services - $69, $54, $200, $146; Research and development - $1,215, $1,573, $3,663, $3,719; Sales and marketing - $816, $1,661, $2,581, $3,323; General administrative - $759, $1,269, $2,521, $2,840;

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Products
Stock-based compensation	$ 137	$ 120	$ 349	$ 338
Services
Stock-based compensation	69	54	200	146
Research and development
Stock-based compensation	1,215	1,573	3,663	3,719
Sales and marketing
Stock-based compensation	816	1,661	2,581	3,323
General and administrative
Stock-based compensation	$ 759	$ 1,269	$ 2,521	$ 2,840

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016
Operating activities:
Net loss	$ (70,166)	$ (15,919)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Stock-based compensation	9,314	10,366
Depreciation and amortization	7,632	6,282
Amortization of intangible assets	813	4,991
Loss on retirement of property and equipment	148	0
Amortization of premium (discount) related to available-for-sale securities	(7)	337
Changes in operating assets and liabilities:
Accounts receivable, net	7,109	(10,104)
Inventory	8,224	7,477
Deferred cost of revenue	11,904	(9,800)
Prepaid expenses and other assets	(320)	(6,058)
Accounts payable	5,543	(356)
Accrued liabilities	(10,132)	13,974
Deferred revenue	1,310	4,383
Other long-term liabilities	3	(313)
Net cash provided by (used in) operating activities	(28,625)	5,260
Investing activities:
Purchases of property and equipment	(6,786)	(5,364)
Purchases of marketable securities	(8,732)	0
Sales of marketable securities	5,051	0
Maturities of marketable securities	24,841	20,170
Net cash provided by investing activities	14,374	14,806
Financing activities:
Proceeds from exercise of stock options	29	14
Proceeds from employee stock purchase plan	673	2,905
Payments for repurchases of common stock	0	(12,809)
Taxes paid for awards vested under equity incentive plan	(2,743)	(1,787)
Proceeds from line of credit	68,534	0
Repayment of line of credit	(38,534)	0
Payments to originate the line of credit	(186)	0
Net cash provided by (used in) financing activities	27,773	(11,677)
Effect of exchange rate changes on cash and cash equivalents	303	(251)
Net increase in cash and cash equivalents	13,825	8,138
Cash and cash equivalents at beginning of period	50,359	23,626
Cash and cash equivalents at end of period	$ 64,184	$ 31,764

Company and Basis of Presentati

Company and Basis of Presentation	9 Months Ended
	Sep. 30, 2017
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Company and Basis of Presentation	Company and Basis of Presentation Company Calix, Inc. (together with its subsidiaries, “Calix,” the “Company,” “our,” “we,” or “us”) was incorporated in August 1999, and is a Delaware corporation. The Company is a leading global provider of broadband communications access platforms, systems and software for fiber- and copper-based network architectures and a pioneer in software defined access and cloud products focused on access networks and the subscriber. Calix’s portfolio combines Access eXtensible Operating System (“AXOS”), a software platform for access, with Calix Cloud, the Company’s innovative cloud products for network data analytics and subscriber experience assurance. Together they enable communications service providers (“CSPs”) to transform their networks and enhance how they connect to their residential and business subscribers. The Company enables CSPs to provide a wide range of revenue-generating services, from basic voice and data to advanced broadband services, over legacy and next-generation access networks. The Company focuses solely on CSP access networks, the portion of the network that governs available bandwidth and determines the range and quality of services that can be offered to subscribers. Basis of Presentation The accompanying unaudited condensed consolidated financial statements, including the accounts of Calix, Inc. and its wholly-owned subsidiaries, have been prepared in accordance with the requirements of the U.S. Securities and Exchange Commission (“SEC”) for interim reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. generally accepted accounting principles (“GAAP”) can be condensed or omitted. In the opinion of management, the financial statements include all normal and recurring adjustments that are considered necessary for the fair presentation of the Company’s financial position and operating results. All significant intercompany balances and transactions have been eliminated in consolidation. The Condensed Consolidated Balance Sheet at December 31, 2016 has been derived from the audited financial statements at that date. The results of the Company’s operations can vary during each quarter of the year. Therefore, the results and trends in these interim financial statements may not be the same as those for the full year or any future periods. The information included in this Quarterly Report on Form 10-Q should be read in conjunction with the audited financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2016 . The Company’s fiscal year begins on January 1 st and ends on December 31 st . Quarterly periods are based on a 4-4-5 calendar with the first, second and third quarters ending on the 13 th Saturday of each fiscal period. As a result, the Company had five more days in the nine months ended September 30, 2017 than in the nine months ended September 24, 2016 . The preparation of financial statements in conformity with GAAP for interim financial reporting requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Actual results could differ from those estimates. Prior Period Recast The Company’s revenue from services for the three and nine months ended September 30, 2017 represents more than 10% of its total revenue; hence, the services revenue and the associated cost of revenue are presented separately in the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss). Services include professional services, customer support, software maintenance, extended warranty subscriptions, training and managed services. Accordingly, revenue and cost of revenue for the three and nine months ended September 24, 2016 are recast solely to conform with the current period presentation. The recast does not affect total revenue, total cost of revenue, gross profit, operating expenses or net income (loss).

Significant Accounting Policies

Significant Accounting Policies	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies The Company’s significant accounting policies are disclosed in its Annual Report on Form 10-K for the year ended December 31, 2016 . The Company’s significant accounting policies did not change during the nine months ended September 30, 2017 , except for those impacted by the newly adopted accounting standards below. Newly Adopted Accounting Standards Stock-Based Compensation In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which simplifies several aspects of the accounting for employee share-based payment transactions for both public and nonpublic entities, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted ASU 2016-09 in the first quarter of 2017 and had the following impact: a. Accounting for Income Taxes - The primary impact of the adoption was the recognition of excess tax benefits and tax deficiencies through the statement of operations when the awards vest or are settled rather than through paid-in capital. The new guidance eliminates the requirement to delay the recognition of excess tax benefits until it reduces current taxes payable and requires the recognition of excess tax benefits and tax deficiencies in the period they arise. The Company adopted this guidance on a modified retrospective basis beginning on January 1, 2017, and the adoption had a cumulative-effect adjustment to the beginning balance of deferred tax asset and was fully offset by the corresponding valuation allowance as of January 1, 2017. The adoption had no cumulative-effect adjustment on January 1, 2017 accumulated deficit as the Company’s net operating loss carryforwards are offset by a full valuation allowance. b. Classification of Excess Tax Benefits on the Statement of Cash Flows - ASU 2016-09 requires all tax-related cash flows resulting from share-based payments to be reported as operating activities on the statement of cash flows, a change from the current requirement to present windfall tax benefits as an inflow from financing activities and an outflow from operating activities. The Company adopted this guidance prospectively beginning on January 1, 2017. The adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. c. Forfeitures - The Company has historically recognized stock-based compensation expense net of estimated forfeitures on all unvested awards and elected to continuously do so with the adoption of this new guidance. Hence, the adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. d. Minimum Statutory Tax Withholding Requirements - ASU 2016-09 allows companies to withhold an amount up to the employee’s maximum individual tax rate in the relevant jurisdiction without resulting in liability classification of the award. The Company adopted this guidance using a modified retrospective approach. The adoption had no impact on the January 1, 2017 accumulated deficit as the Company had no outstanding liability awards that would otherwise qualify for equity classification under this new guidance. e. Classification of Employee Taxes Paid on the Statement of Cash Flows When an Employer Withholds Shares for Tax-Withholding Purposes - ASU 2016-09 clarifies that all cash payments made to taxing authorities on the employees’ behalf for withheld shares should be presented as financing activities on the statement of cash flows. The Company has historically presented the taxes paid related to net share settlement of equity awards as a financing activity on the statements of cash flows. Hence, the adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. Inventory In July 2015, the FASB issued Accounting Standards Update No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory (“ASU 2015-11”), which requires measurement of inventory at lower of cost and net realizable value, versus lower of cost or market. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. The Company adopted ASU 2015-11 prospectively beginning on January 1, 2017. The adoption of this standard had no material impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which requires recognition of an asset and liability for lease arrangements longer than twelve months. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. Early application is permitted, and it is required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company is not planning to early adopt, and accordingly, it will adopt the new standard effective January 1, 2019. The Company intends to elect the available practical expedients on adoption. The Company is currently assessing the potential impact of adopting this new guidance on its consolidated financial statements. The Company expects its assets and liabilities to increase as the new standard requires recognition of right-of-use assets and lease liabilities for operating leases, but does not expect any material impact on its income (loss) from operations or net income (loss) as a result of the adoption of this standard. Revenue from Contracts with Customers In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which provides guidance for revenue recognition. ASU 2014-09 supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and most industry-specific guidance. Additionally, it supersedes some cost guidance included in Subtopic 605-35, Revenue Recognition-Construction-Type and Production-Type Contracts, and creates new Subtopic 340-40, Other Assets and Deferred Costs-Contracts with Customers. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the previous guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. On August 12, 2015, the FASB issued Accounting Standards Update No. 2015-14, Revenue from Contracts with Customers (Topic 606), Deferral of the Effective Date (“ASU 2015-14”) to defer the effective date of ASU 2014-09 by one year. ASU 2015-14 permits early adoption of the new revenue standard, but not before its original effective date. In April 2016, the FASB issued Accounting Standards Update No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”) which further clarifies guidance related to identifying performance obligations and licensing implementation guidance contained in ASU 2014-09. In May 2016, the FASB issued Accounting Standards Update No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”) which addresses narrow-scope improvements to the guidance on collectibility, non-cash consideration, and completed contracts at transition and provides a practical expedient for contract modifications at transition and an accounting policy election related to the presentation of sales taxes and other similar taxes collected from customers. The new standard permits adoption either by using (i) a full retrospective approach for all periods presented in the period of adoption or (ii) a modified retrospective approach with the cumulative effect of initially applying the new standard recognized at the date of initial application and providing certain additional disclosures. The Company will adopt the new standard effective January 1, 2018 using the modified retrospective transition method applied to those contracts which are not completed as of that date. The Company has reached preliminary conclusions on key accounting assessments related to the standard and is in the process of evaluating the impact of the new standard on its accounting policies, processes and system requirements. The Company has assigned internal resources in addition to the engagement of third party service providers to assist in its evaluation. Additionally, the Company expects to make investments in new systems or enhancement of existing systems to enable timely and accurate reporting under the new standard. While the Company continues to perform further assessment of all potential impacts under the new standard, the Company expects the timing of revenue recognition to be accelerated for certain performance obligations related to certain revenue arrangements which are currently deferred until customer acceptance. Depending on the outcome of the Company’s final evaluation, the timing of when revenue is recognized could change significantly for those revenue arrangements under the new standard. In connection with the adoption of the new revenue standard, the Company will also adopt ASC 340-40, Other Assets and Deferred Costs - Contracts with Customers, with respect to capitalization and amortization of incremental costs of obtaining a contract effective January 1, 2018. As a result, the Company may need to capitalize additional costs of obtaining a contract, including sales commissions, as the guidance requires the capitalization of all incremental costs incurred to obtain a contract with a customer that it would not have incurred if the contract had not been obtained, provided it expects to recover the costs. The Company expects that sales commissions as a result of obtaining customer contracts are recoverable, and as a result, the Company will defer certain sales commissions and amortize them over the period that the related revenue is recognized. While the Company continues to assess all the potential impacts of the new standard, including the areas described above, and anticipates this standard could have a material impact on its consolidated financial statements, the Company is not able to quantify or cannot reasonably estimate quantitative information related to the impact of the new standard on its consolidated financial statements at this time. Concentration of Customer Risk The Company had one customer that accounted for more than 10% of its total revenue for the three months ended September 30, 2017 and two customers that each accounted for more than 10% of its total revenue for the nine months ended September 30, 2017 . These two customers each accounted for more than 10% of the Company’s total revenue for the three and nine months ended September 24, 2016 . These two customers together represented 41% and 43% of the Company’s total revenue for the three and nine months ended September 30, 2017 , respectively, and 37% and 34% for the three and nine months ended September 24, 2016 , respectively. One of these two customers represented more than 10% of the Company’s accounts receivable as of September 30, 2017 and each of these two customers represented more than 10% of the Company’s accounts receivable as of December 31, 2016 .

Cash, Cash Equivalents and Mark

Cash, Cash Equivalents and Marketable Securities	9 Months Ended
	Sep. 30, 2017
Cash and Cash Equivalents [Abstract]
Cash, Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities The Company has invested its excess cash primarily in money market funds and highly liquid marketable securities such as corporate debt instruments, commercial paper and U.S. government agency securities. The Company considers all investments with maturities of three months or less when purchased to be cash equivalents. Marketable securities represent highly liquid corporate debt instruments, commercial paper and U.S. government agency securities with maturities greater than 90 days at date of purchase. Marketable securities with maturities greater than one year are classified as current because management considers all marketable securities to be available for current operations. Cash equivalents are stated at amounts that approximate fair value based on quoted market prices. Marketable securities are recorded at their fair values. The Company’s investments have been classified and accounted for as available-for-sale. Such investments are recorded at fair value and unrealized holding gains and losses are reported as a separate component of accumulated other comprehensive income (loss) in the stockholders’ equity until realized. Realized gains and losses on sales of marketable securities, if any, are determined on the specific identification method and are reclassified from accumulated other comprehensive income (loss) to results of operations as other income (expense). The Company, to date, has not determined that any of the unrealized losses on its investments are considered to be other-than-temporary. The Company reviews its investment portfolio to determine if any security is other-than-temporarily impaired, which would require the Company to record an impairment charge in the period any such determination is made. In making this judgment, the Company evaluates, among other things: the duration and extent to which the fair value of a security is less than its cost; the financial condition of the issuer and any changes thereto; and the Company’s intent and ability to hold its investment for a period of time sufficient to allow for any anticipated recovery in market value, or whether the Company will more likely than not be required to sell the security before recovery of its amortized cost basis. The Company has evaluated its investments as of September 30, 2017 and has determined that no investments with unrealized losses are other-than-temporarily impaired. No investments have been in a continuous loss position for greater than one year. Cash, cash equivalents and marketable securities consisted of the following (in thousands): September 30, December 31, Cash and cash equivalents: Cash $ 55,058 $ 34,340 Money market funds 9,126 15,020 Commercial paper — 999 Total cash and cash equivalents 64,184 50,359 Marketable securities: Corporate debt securities — 17,272 Commercial paper 2,400 6,275 U.S. government agency securities 4,198 4,201 Total marketable securities 6,598 27,748 $ 70,782 $ 78,107 The carrying amounts of the Company’s money market funds approximate their fair values due to their nature, duration and short maturities. As of September 30, 2017 , all marketable securities were due in one year or less; and the amortized cost and fair value of marketable securities were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 2,401 $ — $ (1 ) $ 2,400 U.S. government agency securities 4,200 — (2 ) 4,198 $ 6,601 $ — $ (3 ) $ 6,598 As of December 31, 2016 , the amortized cost and fair value of marketable securities were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate debt securities $ 17,279 $ 1 $ (8 ) $ 17,272 Commercial paper 6,275 — — 6,275 U.S. government agency securities 4,200 1 — 4,201 $ 27,754 $ 2 $ (8 ) $ 27,748

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The Company measures its cash equivalents and marketable securities at fair value on a recurring basis. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. The Company utilizes the following three-tier value hierarchy which prioritizes the inputs used in measuring fair value: Level 1 – Observable inputs that reflect quoted prices (unadjusted) for identical assets or liabilities in active markets. Level 2 – Observable inputs other than quoted prices included in Level 1 for similar instruments in active markets, quoted prices for identical or similar instruments in markets that are not active, and model-driven valuations in which all significant inputs and significant value drivers are observable in active markets. Level 3 – Unobservable inputs to the valuation derived from fair valuation techniques in which one or more significant inputs or significant value drivers are unobservable. The following table sets forth the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 , based on the three-tier fair value hierarchy (in thousands): As of September 30, 2017 Level 1 Level 2 Total Money market funds $ 9,126 $ — $ 9,126 Commercial paper — 2,400 2,400 U.S. government agency securities — 4,198 4,198 $ 9,126 $ 6,598 $ 15,724 As of December 31, 2016 Level 1 Level 2 Total Money market funds $ 15,020 $ — $ 15,020 Corporate debt securities — 17,272 17,272 Commercial paper — 7,274 7,274 U.S. government agency securities — 4,201 4,201 $ 15,020 $ 28,747 $ 43,767 The fair values of money market funds classified as Level 1 were derived from quoted market prices as active markets for these instruments exist. The fair values of corporate debt securities, commercial paper and U.S. government agency securities classified as Level 2 were derived from quoted market prices for similar instruments indexed to prevailing market yield rates. The Company has no level 3 financial assets. The Company did not have any transfers between Level 1 and Level 2 of the fair value hierarchy during the nine months ended September 30, 2017 and September 24, 2016 .

Goodwill

Goodwill	9 Months Ended
	Sep. 30, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill Goodwill was recorded as a result of the Company’s acquisitions of Occam Networks, Inc. (“Occam”) in February 2011 and Optical Solutions, Inc. in February 2006. This goodwill is not deductible for tax purposes, and there have been no adjustments to goodwill since the acquisition dates. Goodwill is not amortized but instead is subject to an annual impairment test or more frequently if events or changes in circumstances indicate that it may be impaired. The Company evaluates goodwill on an annual basis at the end of the second quarter of each year. Management has determined that the Company operates as a single reporting unit and, therefore, evaluates goodwill impairment at the enterprise level. Management assessed qualitative factors to determine whether it was more likely than not (that is, a likelihood of more than 50 percent) that the fair value of the Company was less than its carrying amount, including goodwill, as of July 1, 2017 . In assessing the qualitative factors, management considered the impact of these key factors: macro-economic conditions, industry and market environment, overall financial performance of the Company, cash flow from operating activities, market capitalization and stock price. Management concluded that the fair value of the Company was more likely than not greater than its carrying amount as of July 1, 2017 . As such, it was not necessary to perform the two-step goodwill impairment test at the time. There have been no significant events or changes in circumstances subsequent to the 2017 annual impairment test that would more likely than not indicate that the carrying value of goodwill may have been impaired as of September 30, 2017 . Therefore, there was no impairment to the carrying value of the Company’s goodwill as of September 30, 2017 .

Balance Sheet Details

Balance Sheet Details	9 Months Ended
	Sep. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	Balance Sheet Details Accounts receivable, net consisted of the following (in thousands): September 30, December 31, Accounts receivable $ 45,630 $ 52,792 Allowance for doubtful accounts (550 ) (518 ) Product return reserve (853 ) (938 ) $ 44,227 $ 51,336 Inventory consisted of the following (in thousands): September 30, December 31, Raw materials $ 1,082 $ 1,827 Finished goods 35,239 42,718 $ 36,321 $ 44,545 Property and equipment, net consisted of the following (in thousands): September 30, December 31, Test equipment $ 46,580 $ 43,580 Computer equipment and software 33,652 30,306 Furniture and fixtures 2,890 2,831 Leasehold improvements 6,759 6,898 Total 89,881 83,615 Accumulated depreciation and amortization (72,884 ) (65,631 ) $ 16,997 $ 17,984 Accrued liabilities consisted of the following (in thousands): September 30, December 31, Accrued compensation and related benefits $ 23,890 $ 19,541 Accrued professional and consulting fees 12,222 8,205 Accrued warranty and retrofit 8,454 12,214 Advance customer payments 5,211 20,726 Accrued excess and obsolete inventory at contract manufacturers 1,819 1,327 Accrued customer rebates 828 1,931 Accrued restructuring charges 195 — Accrued other 6,782 5,771 $ 59,401 $ 69,715 Advance customer payments as of September 30, 2017 and December 31, 2016 primarily included $3.4 million and $20.3 million , respectively, which the Company received as payments in advance of completion of final customer acceptance of the products and services provided in connection with turnkey network improvement projects for a customer. Deferred revenue consisted of the following (in thousands): September 30, December 31, Current: Products and services $ 24,512 $ 24,472 Extended warranty 3,716 3,382 28,228 27,854 Long-term: Products and services 18 22 Extended warranty 21,155 20,215 21,173 20,237 $ 49,401 $ 48,091 Deferred cost of revenue consisted of costs incurred for products and services for which revenue has been deferred or not yet earned.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Lease Commitments The Company leases office space under non-cancelable operating leases. Certain of the Company’s operating leases contain renewal options and rent acceleration clauses. Future minimum payments under the non-cancelable operating leases consisted of the following as of September 30, 2017 (in thousands): Period Minimum Future Lease Payments Remainder of 2017 $ 756 2018 2,794 2019 1,082 2020 738 2021 286 Thereafter 19 $ 5,675 The Company leases its primary office space in Petaluma, California under a lease agreement (“Petaluma Lease”) that expires February 2019. On January 28, 2013, the Company entered into an amendment to its Petaluma Lease ("Amendment") to extend the lease term to February 2019. In connection with the Petaluma Lease and the Amendment, the Company received lease incentives of $1.2 million and $0.4 million , respectively, which can be used for leasehold improvements or be applied as credits to rent payments. The Company capitalized the full amount of the lease incentives upon inception of the respective agreement and these incentives are being amortized to reduce rent expense over the extended lease term. As of September 30, 2017 , total unamortized lease incentive is not significant. Payments under the Company’s operating leases that escalate over the term of the lease are recognized as rent expense on a straight-line basis. The above table also includes future minimum lease payments primarily for our facilities in Minneapolis, Minnesota; Nanjing, China; Richardson, Texas; and San Jose, and Santa Barbara, California, which expire at various dates through 2022. For the three and nine months ended September 30, 2017 , total rent expense of the Company was $0.9 million and $2.7 million , respectively. For the three and nine months ended September 24, 2016 , total rent expense of the Company was $0.9 million and $2.6 million , respectively. Purchase Commitments The Company’s primary contract manufacturers place orders for component inventory in advance based upon the Company’s build forecasts in order to reduce manufacturing lead times and ensure adequate component supply. The components are used by the contract manufacturers to build the products included in the build forecasts. The Company generally does not take ownership of the components held by contract manufacturers. The Company places purchase orders with its contract manufacturers in order to fulfill its monthly finished product inventory requirements. The Company incurs a liability when the contract manufacturer has converted the component inventory to a finished product and takes ownership of the inventory when transferred to the designated shipping warehouse. In the event of termination of services with a contract manufacturer, the Company may be required to purchase the remaining components inventory held by the contract manufacturer as well as any outstanding orders pursuant to the contractual provisions with such contract manufacturer. As of September 30, 2017 , the Company had approximately $62.6 million of outstanding purchase commitments for inventories to be delivered by its suppliers, including contract manufacturers, within one year. The Company has from time to time, and subject to certain conditions, reimbursed its primary contract manufacturer for component inventory purchases when this inventory has been rendered excess or obsolete, for example due to manufacturing and engineering change orders resulting from design changes, manufacturing discontinuation of parts by its suppliers, or in cases where inventory levels greatly exceed projected demand. The estimated excess and obsolete inventory liabilities related to such manufacturing and engineering change orders and other factors, which are included in accrued liabilities in the accompanying balance sheets, were $1.8 million and $1.3 million as of September 30, 2017 and December 31, 2016 , respectively. The Company records these amounts in cost of products and services in the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss). Contingencies The Company evaluates the circumstances regarding outstanding and potential litigation and other contingencies on a quarterly basis to determine whether there is at least a reasonable possibility that a loss exists requiring accrual or disclosure, and if so, whether an estimate of the possible loss or range of loss can be made, or whether such an estimate cannot be made. When a loss is probable and reasonably estimable, the Company accrues for such amount based on its estimate of the probable loss considering information available at the time. When a loss is reasonably possible, the Company discloses the estimated possible loss or range of loss in excess of amounts accrued if material. Except as otherwise disclosed below, the Company does not believe that there was a reasonable possibility that a material loss may have been incurred during the period presented with respect to the matters disclosed. Accrued Warranty and Retrofit The Company provides a standard warranty for its hardware products. Hardware generally has a one -, three - or five -year standard warranty from the date of shipment. Under certain circumstances, the Company also provides fixes on specifically identified performance failures for products that are outside of the standard warranty period and recognizes estimated costs related to retrofit activities upon identification of such product failures. The Company accrues for potential warranty and retrofit claims based on the Company’s historical product failure rates and historical costs incurred in correcting product failures along with other relevant information related to any specifically identified product failures. The Company’s warranty and retrofit accruals are based on estimates of losses that are probable based on information available. The adequacy of the accrual is reviewed on a periodic basis and adjusted, if necessary, based on additional information as it becomes available. Changes in the Company’s warranty and retrofit reserves in the periods as indicated were as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Balance at beginning of period $ 9,265 $ 9,152 $ 12,214 $ 9,564 Provision for warranty and retrofit charged to cost of revenue 2,057 3,180 5,661 6,292 Utilization of reserve (2,868 ) (948 ) (9,421 ) (4,073 ) Adjustments to pre-existing reserve — (11 ) — (410 ) Balance at end of period $ 8,454 $ 11,373 $ 8,454 $ 11,373 Litigation From time to time, the Company is involved in various legal proceedings arising from the normal course of business activities. The Company is not currently a party to any legal proceedings that, if determined adversely to the Company, in management’s opinion, are currently expected to individually or in the aggregate have a material adverse effect on the Company’s business, operating results or financial condition taken as a whole. Indemnifications The Company from time to time enters into contracts that require it to indemnify various parties against claims from third parties. These contracts primarily relate to (i) certain real estate leases, under which the Company may be required to indemnify property owners for environmental and other liabilities, and other claims arising from the Company’s use of the applicable premises, (ii) agreements with the Company’s officers, directors and certain employees, under which the Company may be required to indemnify such persons for liabilities arising out of their relationship with the Company, (iii) contracts under which the Company may be required to indemnify customers against third-party claims that a Company product infringes a patent, copyright or other intellectual property right and (iv) procurement or license agreements, under which the Company may be required to indemnify licensors or vendors for certain claims that may be brought against them arising from the Company’s acts or omissions with respect to the supplied products or technology. Because any potential obligation associated with these types of contractual provisions are not quantified or stated, the overall maximum amount of the obligation cannot be reasonably estimated. Historically, the Company has not been required to make payments under these obligations, and no liabilities have been recorded for these obligations in the accompanying Condensed Consolidated Balance Sheets.

Net Income (Loss) Per Common Sh

Net Income (Loss) Per Common Share	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Net Income (Loss) Per Common Share	Net Income (Loss) Per Common Share The following table sets forth the computation of basic and diluted net income (loss) per common share for the periods indicated (in thousands, except per share data): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Numerator: Net income (loss) $ (17,853 ) $ 636 $ (70,166 ) $ (15,919 ) Denominator: Weighted-average common shares outstanding used to compute basic net income (loss) per share 50,336 48,773 49,960 48,578 Effect of dilutive common stock equivalents — 536 — — Weighted-average common shares outstanding used to compute diluted net income (loss) per share 50,336 49,309 49,960 48,578 Net income (loss) per common share: Basic $ (0.35 ) $ 0.01 $ (1.40 ) $ (0.33 ) Diluted $ (0.35 ) $ 0.01 $ (1.40 ) $ (0.33 ) Potentially dilutive shares, weighted average 5,741 3,951 5,704 5,794 Potentially dilutive shares have been excluded from the computation of diluted net loss per common share when their effect is antidilutive. These antidilutive shares were primarily from stock options, restricted stock units and performance restricted stock units. For each of the periods presented where the Company reported a net loss, the effect of all potentially dilutive securities would be antidilutive, and as a result diluted net loss per common share is the same as basic net loss per common share.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity Equity Incentive Plans As of September 30, 2017 , the Company currently maintains two equity incentive plans, the 2002 Stock Plan and the 2010 Equity Incentive Award Plan (together, the “Plans”). These plans were approved by the stockholders and are described in the Company’s Annual Report on Form 10-K filed with the SEC on February 28, 2017 . The Company also maintains a Long Term Incentive Program under the 2010 Equity Incentive Award Plan. Under the Long Term Incentive Program, certain key employees of the Company are eligible for equity awards based on the Company’s stock price performance. To date, awards granted under the Plans consist of stock options, restricted stock units (“RSUs”) and performance restricted stock units (“PRSUs”). Stock Options During the three and nine months ended September 30, 2017 , 1,565,000 shares of stock options were granted with a weighted-average grant date fair value of $3.45 per share, of which 1,165,000 shares with a weighted-average grant date fair value of $3.43 per share were performance-based stock option awards which were granted by the Company to its executives. These performance-based stock option awards contain a one -year performance period and a subsequent three -year service period. The performance target is based on a combination of the Company’s revenue and non-GAAP operating income during the performance period and accounted for as a performance condition. After the one -year performance period, if the performance target is met and subject to certification by the Compensation Committee of the Company’s board of directors, each performance-based stock option award shall vest with respect to 25% of the earned shares on February 6, 2018 and 6.25% of the earned shares on the quarterly anniversary thereafter, subject to the executive’s continuous service with the Company from the grant date through the respective vesting dates. If the performance target is not met, all performance-based stock options granted under this award shall be immediately forfeited and canceled without vesting of any shares. During the three months ended September 30, 2017 , no stock options were exercised. During the nine months ended September 30, 2017 , 5,000 shares of stock options were exercised at a weighted-average exercise price of $5.99 per share. As of September 30, 2017 , unrecognized stock-based compensation expense of $3.4 million related to stock options, net of estimated forfeitures, is expected to be recognized over a weighted-average period of 2.3 years. Restricted Stock Units During the three months ended September 30, 2017 , 92,266 shares of RSUs were granted with a weighted-average grant date fair value of $6.34 per share. During the nine months ended September 30, 2017 , 505,236 shares of RSUs were granted with a weighted-average grant date fair value of $6.75 per share. During the three months ended September 30, 2017 , 107,107 shares of RSUs vested, net of shares withheld for statutory income tax purposes, and were converted to an equivalent number of shares of common stock. During the nine months ended September 30, 2017 , 670,095 shares of RSUs vested, net of shares withheld for statutory income tax purposes, and were converted to an equivalent number of shares of common stock. Taxes withheld from employees of $0.1 million were remitted to the relevant taxing authorities during the three months ended September 30, 2017 . Taxes withheld from employees of $1.8 million were remitted to the relevant taxing authorities during the nine months ended September 30, 2017 . As of September 30, 2017 , unrecognized stock-based compensation expense of $10.2 million related to RSUs, net of estimated forfeitures, was expected to be recognized over a weighted-average period of 2.2 years. Performance Restricted Stock Units In 2016, the Company granted PRSUs to its executives with a one -year performance period and a subsequent two -year service period. The performance target for these particular performance-based awards is based on the Company’s revenue during the performance period and accounted for as a performance condition. After the one -year performance period, if the performance target is met and subject to certification by the Compensation Committee of the Company’s board of directors, each PRSU award shall vest with respect to 50% of the PRSUs subject to the award in February 2017, 25% in February 2018 and 25% in February 2019, subject to the executive’s continuous service with the Company from the grant date through the respective vesting dates. If the performance target is not met, all PRSUs granted under this award shall be immediately forfeited and canceled without vesting of any shares. During the three months ended September 30, 2017 , no PRSUs vested. During the nine months ended September 30, 2017 , 325,000 shares of PRSUs vested and were converted into 195,656 shares of common stock, net of shares withheld for statutory income tax purposes. Taxes withheld from employees of $0.9 million were remitted to the relevant taxing authorities during the nine months ended September 30, 2017 . As of September 30, 2017 , unrecognized stock-based compensation expense of $0.3 million related to PRSUs, net of estimated forfeitures, is expected to be recognized over a weighted-average period of 10.3 months. Employee Stock Purchase Plans The Company’s Amended and Restated Employee Stock Purchase Plan (“Restated ESPP”) allows employees to purchase shares of the Company’s common stock through payroll deductions of up to 15 percent of their annual compensation subject to certain Internal Revenue Code limitations. In addition, no participant may purchase more than 2,000 shares of common stock in each offering period. The offering periods under the Restated ESPP were six-month periods commencing on November 2 nd and May 2 nd of each year, effective November 2, 2015. In July 2016, the Compensation Committee of the Company’s board of directors approved a change in those six-month period commencement dates to May 15 th and November 15 th of each year, effective May 15, 2017. The ending date of the Restated ESPP offering period which commenced on November 2, 2016 was extended until May 14, 2017 as a result of this change. The price of common stock purchased under the Restated ESPP is 85 percent of the lower of the fair market value of the common stock on the commencement date and the end date of each six -month offering period. As of September 30, 2017 , there were 3,000,217 shares available for issuance under the Restated ESPP. During the three months ended September 30, 2017 , no shares were purchased under the Restated ESPP. During the nine months ended September 30, 2017 , 119,011 shares were purchased under the Restated ESPP. As of September 30, 2017 , unrecognized stock-based compensation expense of $0.2 million related to the Restated ESPP is expected to be recognized over a remaining service period of 1.5 months. On March 30, 2017, the Company’s board of directors, upon recommendation of the Compensation Committee, approved the adoption of the Calix, Inc. 2017 Nonqualified Employee Stock Purchase Plan (“Nonqualified ESPP”). The Nonqualified ESPP was approved by our stockholders on May 17, 2017, with the initial offering period commencing July 1, 2017. Under the Nonqualified ESPP, eligible employees can purchase shares of the Company’s common stock through payroll deductions of up to 25 percent of their annual compensation. Eligible employees have the right to (a) purchase the maximum number of whole shares of common stock that can be purchased with the elected payroll deductions during each offering period for which the employee is enrolled at a purchase price equal to the closing price of the Company’s common stock on the last day of such offering period and (b) receive an equal number of shares of the Company’s common stock that are subject to a risk of forfeiture in the event the employee terminates employment within the one year period immediately following the purchase date. The Nonqualified ESPP provides two six -month offering periods, from January 1 through June 30 and July 1 through December 31 of each year. The maximum number of shares of common stock currently authorized for issuance under the Nonqualified ESPP is 1,000,000 shares, with a maximum of 500,000 shares allocated per purchase period. As of September 30, 2017 , unrecognized stock-based compensation expense of $1.2 million related to the Nonqualified ESPP is expected to be recognized over a remaining service period of 1.3 years. Stock-Based Compensation Expense Stock-based compensation expense associated with stock options, RSUs, PRSUs and purchase rights under the Restated ESPP and Nonqualified ESPP is measured at the grant date based on the fair value of the award, and is recognized, net of forfeitures, as expense over the remaining requisite service period on a straight-line basis. The fair value of stock option and employee stock purchase right under the Restated ESPP is estimated at the grant date using the Black-Scholes option valuation model. The fair value of RSUs and Nonqualified ESPP is based on closing market price of the Company’s common stock on the date of grant. Stock-based compensation expense associated with PRSUs with graded vesting features and which contain both a performance and a service condition is measured based on the closing market price of the Company’s common stock on the date of grant, and is recognized, net of forfeitures, as expense over the requisite service period using the graded vesting attribution method. Stock-based compensation expense associated with performance-based stock options with graded vesting features and which contain both a performance and a service condition is measured based on fair value of stock option estimated at the grant date using the Black-Scholes option valuation model, and is recognized, net of forfeitures, as expense over the requisite service period using the graded vesting attribution method. Compensation expense associated with PRSUs and performance-based stock option awards with graded vesting features and which contain both a performance and a service condition is only recognized if the Company has determined that it is probable that the performance condition will be met. The Company reassesses the probability of vesting at each reporting period and adjusts compensation expense based on its probability assessment. In February 2017, the Compensation Committee of the Company’s board of directors determined that the performance condition related to PRSUs granted to executives in 2016 was met based on the Company’s actual revenue recognized during 2016. The probability of meeting the performance condition related to performance-based stock option awards granted to executives in August 2017 was assessed to be unlikely as of September 30, 2017 ; as such, no stock-based compensation expense was recognized for these performance-based stock option awards as of September 30, 2017 . The fair value of PRSUs with a market condition is estimated on the date of award using a Monte Carlo simulation model to estimate the total shareholder return of the Company’s stock in relation to the peer group over each performance period. Compensation cost on PRSUs with a market condition is not adjusted for subsequent changes in the Company’s stock performance or the level of ultimate vesting.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The table below summarizes the changes in accumulated other comprehensive loss by component for the periods indicated (in thousands): Three Months Ended September 30, 2017 September 24, 2016 Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Balance at beginning of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 ) Other comprehensive income (loss) 4 116 120 (9 ) (87 ) (96 ) Balance at end of period $ (3 ) $ (341 ) $ (344 ) $ 3 $ (229 ) $ (226 ) Nine Months Ended September 30, 2017 September 24, 2016 Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Balance at beginning of period $ (6 ) $ (650 ) $ (656 ) $ (94 ) $ (101 ) $ (195 ) Other comprehensive income (loss) 3 309 312 97 (128 ) (31 ) Balance at end of period $ (3 ) $ (341 ) $ (344 ) $ 3 $ (229 ) $ (226 ) Realized gains and losses on sales of available-for-sale marketable securities, if any, are reclassified from accumulated other comprehensive loss to “Other income (expense)” in the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss).

Credit Facility

Credit Facility	9 Months Ended
	Sep. 30, 2017
Line of Credit Facility [Abstract]
Credit Facility	Credit Facility The Company entered into a credit agreement with Bank of America, N.A. on July 29, 2013 (as amended on December 23, 2015, the “Credit Agreement”). The Credit Agreement provided for a revolving facility in the aggregate principal amount of up to $50.0 million , with any borrowings limited to a maximum consolidated leverage ratio of consolidated funded indebtedness to consolidated EBITDA (as defined in the Credit Agreement). On August 7, 2017, the Company contemporaneously terminated the Credit Agreement in connection with entering into a loan and security agreement (the “Loan Agreement”) with Silicon Valley Bank (“SVB”) . The Loan Agreement provides for a senior secured revolving credit facility with SVB, pursuant to which SVB agreed to make revolving advances available to the Company in a principal amount of up to $30.0 million based on a customary accounts receivable borrowing base, subject to certain exceptions for accounts originating outside the United States and certain specific accounts. The credit facility includes a $10.0 million sublimit for the issuance of letters of credit. The letters of credit issued under the Loan Agreement will reduce, on a dollar-for-dollar basis, the amount available under the credit facility. Additionally, the Company can borrow up to $5.0 million on a non-formula revolver until January 15, 2018, which will reduce, on a dollar-for-dollar basis, the amount available under the credit facility so that at no time will more than $30.0 million in principal amount be outstanding under the Loan Agreement. The credit facility matures and all outstanding amounts become due and payable on August 7, 2019. Subject to certain exceptions, the Company will also be required to pay to SVB a fee of $0.3 million if it terminates the credit facility prior to August 7, 2018. The credit facility is secured by substantially all of the Company’s assets, including the Company’s intellectual property. Loans under the credit facility will bear interest through maturity at a variable annual rate based upon an annual rate of either a prime rate or a LIBOR rate, plus an applicable margin between 0.50% to 1.50% for prime rate advances and between 2.00% and 3.00% for LIBOR advances based on the Company’s maintenance of an applicable liquidity ratio. As of September 30, 2017 , the Company was in compliance with these requirements. The credit facility includes affirmative and negative covenants applicable to the Company and its subsidiaries. Furthermore, the Loan Agreement requires the Company to maintain a liquidity ratio at minimum levels set forth in more detail in the Loan Agreement. The credit facility also includes events of default, the occurrence and continuation of which would provide SVB with the right to demand immediate repayment of any principal and unpaid interest under the credit facility, and to exercise remedies against the Company and the collateral securing the loans under the credit facility. As of September 30, 2017 , the outstanding balance on the line of credit was $30 million .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table presents the provision for income taxes from continuing operations and the effective tax rates for the periods indicated (in thousands, except percentages): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Provision for income taxes $ 225 $ 209 $ 1,075 $ 454 Effective tax rate (1.3 )% 24.7 % (1.6 )% (2.9 )% The income tax provision for the three and nine months ended September 30, 2017 and September 24, 2016 consisted primarily of foreign income taxes. The effective tax rate for the three and nine months ended September 30, 2017 and September 24, 2016 was determined using an estimated annual effective tax rate adjusted for discrete items, if any, that occurred during the respective periods. The Company’s effective tax rate for the three and nine months ended September 30, 2017 and September 24, 2016 is impacted by the change in foreign income tax expense. Deferred tax assets are recognized if realization of such assets is more likely than not. The Company has established and continues to maintain a full valuation allowance against its net deferred tax assets, with the exception of certain foreign deferred tax assets, as the Company does not believe that realization of those assets is more likely than not . The Company’s effective tax rate may be subject to fluctuation during the year as new information is obtained, which may affect the assumptions used to estimate the annual effective tax rate, including factors such as the mix of forecasted pre-tax earnings in the various jurisdictions in which it operates, valuation allowances against deferred tax assets, the recognition or de-recognition of tax benefits related to uncertain tax positions, and changes in or the interpretation of tax laws in jurisdictions where it conducts business .

Restructuring Charges

Restructuring Charges	9 Months Ended
	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Restructuring Charges	Restructuring Charges The Company adopted a restructuring plan in March 2017. This restructuring plan realigns the Company’s business, increasing its focus towards its investments in software defined access and cloud products, while reducing its cost structure in its traditional systems business. The Company began to take action under this plan beginning in March 2017 and recognized $0.6 million and $2.3 million of restructuring charges for the three and nine months ended September 30, 2017 , respectively, consisting primarily of severance and other one-time termination benefits. Restructuring charges are presented separately under operating expenses in the accompanying Condensed Consolidated Statements of Comprehensive Income (Loss). The following table summarizes the activities related to the restructuring charges pursuant to the above restructuring plan (in thousands): Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Liability at beginning of period $ 600 $ — Restructuring charges for the period 612 2,268 Cash payments (1,017 ) (2,073 ) Liability at end of period $ 195 $ 195 The Company currently estimates that this plan will result in pre-tax restructuring charges totaling up to $4.0 million with approximately up to $1.7 million of additional charges expected to be recognized during the fourth quarter of 2017. These charges are primarily cash-based.

Significant Accounting Polici20

Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2017
Accounting Policies [Abstract]
Recent Accounting Pronouncements	Newly Adopted Accounting Standards Stock-Based Compensation In March 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update No. 2016-09, Compensation - Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting (“ASU 2016-09”), which simplifies several aspects of the accounting for employee share-based payment transactions for both public and nonpublic entities, including the accounting for income taxes, forfeitures, and statutory tax withholding requirements, as well as classification in the statement of cash flows. The Company adopted ASU 2016-09 in the first quarter of 2017 and had the following impact: a. Accounting for Income Taxes - The primary impact of the adoption was the recognition of excess tax benefits and tax deficiencies through the statement of operations when the awards vest or are settled rather than through paid-in capital. The new guidance eliminates the requirement to delay the recognition of excess tax benefits until it reduces current taxes payable and requires the recognition of excess tax benefits and tax deficiencies in the period they arise. The Company adopted this guidance on a modified retrospective basis beginning on January 1, 2017, and the adoption had a cumulative-effect adjustment to the beginning balance of deferred tax asset and was fully offset by the corresponding valuation allowance as of January 1, 2017. The adoption had no cumulative-effect adjustment on January 1, 2017 accumulated deficit as the Company’s net operating loss carryforwards are offset by a full valuation allowance. b. Classification of Excess Tax Benefits on the Statement of Cash Flows - ASU 2016-09 requires all tax-related cash flows resulting from share-based payments to be reported as operating activities on the statement of cash flows, a change from the current requirement to present windfall tax benefits as an inflow from financing activities and an outflow from operating activities. The Company adopted this guidance prospectively beginning on January 1, 2017. The adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. c. Forfeitures - The Company has historically recognized stock-based compensation expense net of estimated forfeitures on all unvested awards and elected to continuously do so with the adoption of this new guidance. Hence, the adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. d. Minimum Statutory Tax Withholding Requirements - ASU 2016-09 allows companies to withhold an amount up to the employee’s maximum individual tax rate in the relevant jurisdiction without resulting in liability classification of the award. The Company adopted this guidance using a modified retrospective approach. The adoption had no impact on the January 1, 2017 accumulated deficit as the Company had no outstanding liability awards that would otherwise qualify for equity classification under this new guidance. e. Classification of Employee Taxes Paid on the Statement of Cash Flows When an Employer Withholds Shares for Tax-Withholding Purposes - ASU 2016-09 clarifies that all cash payments made to taxing authorities on the employees’ behalf for withheld shares should be presented as financing activities on the statement of cash flows. The Company has historically presented the taxes paid related to net share settlement of equity awards as a financing activity on the statements of cash flows. Hence, the adoption of ASU 2016-09 as it relates to this matter had no impact to the Company’s consolidated financial statements. Inventory In July 2015, the FASB issued Accounting Standards Update No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory (“ASU 2015-11”), which requires measurement of inventory at lower of cost and net realizable value, versus lower of cost or market. Net realizable value is the estimated selling price in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. The Company adopted ASU 2015-11 prospectively beginning on January 1, 2017. The adoption of this standard had no material impact on the Company’s consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted Leases In February 2016, the FASB issued Accounting Standards Update No. 2016-02, Leases (Topic 842) (“ASU 2016-02”), which requires recognition of an asset and liability for lease arrangements longer than twelve months. ASU 2016-02 will be effective for the Company beginning in the first quarter of 2019. Early application is permitted, and it is required to recognize and measure leases at the beginning of the earliest period presented using a modified retrospective approach. The Company is not planning to early adopt, and accordingly, it will adopt the new standard effective January 1, 2019. The Company intends to elect the available practical expedients on adoption. The Company is currently assessing the potential impact of adopting this new guidance on its consolidated financial statements. The Company expects its assets and liabilities to increase as the new standard requires recognition of right-of-use assets and lease liabilities for operating leases, but does not expect any material impact on its income (loss) from operations or net income (loss) as a result of the adoption of this standard. Revenue from Contracts with Customers In May 2014, the FASB issued Accounting Standards Update No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”), which provides guidance for revenue recognition. ASU 2014-09 supersedes the revenue recognition requirements in Topic 605, Revenue Recognition, and most industry-specific guidance. Additionally, it supersedes some cost guidance included in Subtopic 605-35, Revenue Recognition-Construction-Type and Production-Type Contracts, and creates new Subtopic 340-40, Other Assets and Deferred Costs-Contracts with Customers. The standard’s core principle is that a company will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the company expects to be entitled in exchange for those goods or services. In doing so, companies will need to use more judgment and make more estimates than under the previous guidance. These may include identifying performance obligations in the contract, estimating the amount of variable consideration to include in the transaction price and allocating the transaction price to each separate performance obligation. On August 12, 2015, the FASB issued Accounting Standards Update No. 2015-14, Revenue from Contracts with Customers (Topic 606), Deferral of the Effective Date (“ASU 2015-14”) to defer the effective date of ASU 2014-09 by one year. ASU 2015-14 permits early adoption of the new revenue standard, but not before its original effective date. In April 2016, the FASB issued Accounting Standards Update No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”) which further clarifies guidance related to identifying performance obligations and licensing implementation guidance contained in ASU 2014-09. In May 2016, the FASB issued Accounting Standards Update No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”) which addresses narrow-scope improvements to the guidance on collectibility, non-cash consideration, and completed contracts at transition and provides a practical expedient for contract modifications at transition and an accounting policy election related to the presentation of sales taxes and other similar taxes collected from customers. The new standard permits adoption either by using (i) a full retrospective approach for all periods presented in the period of adoption or (ii) a modified retrospective approach with the cumulative effect of initially applying the new standard recognized at the date of initial application and providing certain additional disclosures. The Company will adopt the new standard effective January 1, 2018 using the modified retrospective transition method applied to those contracts which are not completed as of that date. The Company has reached preliminary conclusions on key accounting assessments related to the standard and is in the process of evaluating the impact of the new standard on its accounting policies, processes and system requirements. The Company has assigned internal resources in addition to the engagement of third party service providers to assist in its evaluation. Additionally, the Company expects to make investments in new systems or enhancement of existing systems to enable timely and accurate reporting under the new standard. While the Company continues to perform further assessment of all potential impacts under the new standard, the Company expects the timing of revenue recognition to be accelerated for certain performance obligations related to certain revenue arrangements which are currently deferred until customer acceptance. Depending on the outcome of the Company’s final evaluation, the timing of when revenue is recognized could change significantly for those revenue arrangements under the new standard. In connection with the adoption of the new revenue standard, the Company will also adopt ASC 340-40, Other Assets and Deferred Costs - Contracts with Customers, with respect to capitalization and amortization of incremental costs of obtaining a contract effective January 1, 2018. As a result, the Company may need to capitalize additional costs of obtaining a contract, including sales commissions, as the guidance requires the capitalization of all incremental costs incurred to obtain a contract with a customer that it would not have incurred if the contract had not been obtained, provided it expects to recover the costs. The Company expects that sales commissions as a result of obtaining customer contracts are recoverable, and as a result, the Company will defer certain sales commissions and amortize them over the period that the related revenue is recognized. While the Company continues to assess all the potential impacts of the new standard, including the areas described above, and anticipates this standard could have a material impact on its consolidated financial statements, the Company is not able to quantify or cannot reasonably estimate quantitative information related to the impact of the new standard on its consolidated financial statements at this time.

Cash, Cash Equivalents and Ma21

Cash, Cash Equivalents and Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2017
Cash and Cash Equivalents [Abstract]
Summary of cash and cash equivalents	Cash, cash equivalents and marketable securities consisted of the following (in thousands): September 30, December 31, Cash and cash equivalents: Cash $ 55,058 $ 34,340 Money market funds 9,126 15,020 Commercial paper — 999 Total cash and cash equivalents 64,184 50,359 Marketable securities: Corporate debt securities — 17,272 Commercial paper 2,400 6,275 U.S. government agency securities 4,198 4,201 Total marketable securities 6,598 27,748 $ 70,782 $ 78,107
Amortized cost and fair value of marketable securities	As of September 30, 2017 , all marketable securities were due in one year or less; and the amortized cost and fair value of marketable securities were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Commercial paper $ 2,401 $ — $ (1 ) $ 2,400 U.S. government agency securities 4,200 — (2 ) 4,198 $ 6,601 $ — $ (3 ) $ 6,598 As of December 31, 2016 , the amortized cost and fair value of marketable securities were as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Corporate debt securities $ 17,279 $ 1 $ (8 ) $ 17,272 Commercial paper 6,275 — — 6,275 U.S. government agency securities 4,200 1 — 4,201 $ 27,754 $ 2 $ (8 ) $ 27,748

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2017
Fair Value Disclosures [Abstract]
Summary of fair values of financial assets	The following table sets forth the Company’s financial assets measured at fair value on a recurring basis as of September 30, 2017 and December 31, 2016 , based on the three-tier fair value hierarchy (in thousands): As of September 30, 2017 Level 1 Level 2 Total Money market funds $ 9,126 $ — $ 9,126 Commercial paper — 2,400 2,400 U.S. government agency securities — 4,198 4,198 $ 9,126 $ 6,598 $ 15,724 As of December 31, 2016 Level 1 Level 2 Total Money market funds $ 15,020 $ — $ 15,020 Corporate debt securities — 17,272 17,272 Commercial paper — 7,274 7,274 U.S. government agency securities — 4,201 4,201 $ 15,020 $ 28,747 $ 43,767

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	9 Months Ended
	Sep. 30, 2017
Balance Sheet Related Disclosures [Abstract]
Summary of accounts receivable, net	Accounts receivable, net consisted of the following (in thousands): September 30, December 31, Accounts receivable $ 45,630 $ 52,792 Allowance for doubtful accounts (550 ) (518 ) Product return reserve (853 ) (938 ) $ 44,227 $ 51,336
Summary of inventory	Inventory consisted of the following (in thousands): September 30, December 31, Raw materials $ 1,082 $ 1,827 Finished goods 35,239 42,718 $ 36,321 $ 44,545
Summary of property and equipment, net	Property and equipment, net consisted of the following (in thousands): September 30, December 31, Test equipment $ 46,580 $ 43,580 Computer equipment and software 33,652 30,306 Furniture and fixtures 2,890 2,831 Leasehold improvements 6,759 6,898 Total 89,881 83,615 Accumulated depreciation and amortization (72,884 ) (65,631 ) $ 16,997 $ 17,984
Summary of accrued liabilities	Accrued liabilities consisted of the following (in thousands): September 30, December 31, Accrued compensation and related benefits $ 23,890 $ 19,541 Accrued professional and consulting fees 12,222 8,205 Accrued warranty and retrofit 8,454 12,214 Advance customer payments 5,211 20,726 Accrued excess and obsolete inventory at contract manufacturers 1,819 1,327 Accrued customer rebates 828 1,931 Accrued restructuring charges 195 — Accrued other 6,782 5,771 $ 59,401 $ 69,715
Summary of deferred revenue	Deferred revenue consisted of the following (in thousands): September 30, December 31, Current: Products and services $ 24,512 $ 24,472 Extended warranty 3,716 3,382 28,228 27,854 Long-term: Products and services 18 22 Extended warranty 21,155 20,215 21,173 20,237 $ 49,401 $ 48,091

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2017
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum rental payments for operating leases	Future minimum payments under the non-cancelable operating leases consisted of the following as of September 30, 2017 (in thousands): Period Minimum Future Lease Payments Remainder of 2017 $ 756 2018 2,794 2019 1,082 2020 738 2021 286 Thereafter 19 $ 5,675
Product warranty activities	Changes in the Company’s warranty and retrofit reserves in the periods as indicated were as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Balance at beginning of period $ 9,265 $ 9,152 $ 12,214 $ 9,564 Provision for warranty and retrofit charged to cost of revenue 2,057 3,180 5,661 6,292 Utilization of reserve (2,868 ) (948 ) (9,421 ) (4,073 ) Adjustments to pre-existing reserve — (11 ) — (410 ) Balance at end of period $ 8,454 $ 11,373 $ 8,454 $ 11,373

Net Income (Loss) Per Common 25

Net Income (Loss) Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2017
Earnings Per Share [Abstract]
Schedule of net income (loss) per share	The following table sets forth the computation of basic and diluted net income (loss) per common share for the periods indicated (in thousands, except per share data): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Numerator: Net income (loss) $ (17,853 ) $ 636 $ (70,166 ) $ (15,919 ) Denominator: Weighted-average common shares outstanding used to compute basic net income (loss) per share 50,336 48,773 49,960 48,578 Effect of dilutive common stock equivalents — 536 — — Weighted-average common shares outstanding used to compute diluted net income (loss) per share 50,336 49,309 49,960 48,578 Net income (loss) per common share: Basic $ (0.35 ) $ 0.01 $ (1.40 ) $ (0.33 ) Diluted $ (0.35 ) $ 0.01 $ (1.40 ) $ (0.33 ) Potentially dilutive shares, weighted average 5,741 3,951 5,704 5,794

Accumulated Other Comprehensi26

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2017
Equity [Abstract]
Accumulated other comprehensive income details	The table below summarizes the changes in accumulated other comprehensive loss by component for the periods indicated (in thousands): Three Months Ended September 30, 2017 September 24, 2016 Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Balance at beginning of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 ) Other comprehensive income (loss) 4 116 120 (9 ) (87 ) (96 ) Balance at end of period $ (3 ) $ (341 ) $ (344 ) $ 3 $ (229 ) $ (226 ) Nine Months Ended September 30, 2017 September 24, 2016 Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Unrealized Gains and Losses on Available-for-Sale Marketable Securities Foreign Currency Translation Adjustments Total Balance at beginning of period $ (6 ) $ (650 ) $ (656 ) $ (94 ) $ (101 ) $ (195 ) Other comprehensive income (loss) 3 309 312 97 (128 ) (31 ) Balance at end of period $ (3 ) $ (341 ) $ (344 ) $ 3 $ (229 ) $ (226 )

Income Taxes (Tables)

Income Taxes (Tables)	9 Months Ended
	Sep. 30, 2017
Income Tax Disclosure [Abstract]
Schedule of income taxes	The following table presents the provision for income taxes from continuing operations and the effective tax rates for the periods indicated (in thousands, except percentages): Three Months Ended Nine Months Ended September 30, September 24, September 30, September 24, Provision for income taxes $ 225 $ 209 $ 1,075 $ 454 Effective tax rate (1.3 )% 24.7 % (1.6 )% (2.9 )%

Restructuring Charges (Tables)

Restructuring Charges (Tables)	9 Months Ended
	Sep. 30, 2017
Restructuring and Related Activities [Abstract]
Restructuring and Related Costs	The following table summarizes the activities related to the restructuring charges pursuant to the above restructuring plan (in thousands): Three Months Ended September 30, 2017 Nine Months Ended September 30, 2017 Liability at beginning of period $ 600 $ — Restructuring charges for the period 612 2,268 Cash payments (1,017 ) (2,073 ) Liability at end of period $ 195 $ 195

Significant Accounting Polici29

Significant Accounting Policies (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Largest Two Customers | Customer Concentration Risk | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	41.00%	37.00%	43.00%	34.00%

Cash, Cash Equivalents and Ma30

Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016	Sep. 24, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 64,184	$ 50,359	$ 31,764	$ 23,626
Marketable securities	6,598	27,748
Total cash, cash equivalents and marketable securities	70,782	78,107
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Marketable securities	0	17,272
Commercial paper
Cash and Cash Equivalents [Line Items]
Marketable securities	2,400	6,275
U.S. government agency securities
Cash and Cash Equivalents [Line Items]
Marketable securities	4,198	4,201
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	55,058	34,340
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	9,126	15,020
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 0	$ 999

Cash, Cash Equivalents and Ma31

Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 6,601	$ 27,754
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(3)	(8)
Fair Value	6,598	27,748
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		17,279
Gross Unrealized Gains		1
Gross Unrealized Losses		(8)
Fair Value	0	17,272
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,401	6,275
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(1)	0
Fair Value	2,400	6,275
U.S. government agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,200	4,200
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(2)	0
Fair Value	$ 4,198	$ 4,201

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 6,598	$ 27,748
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	15,724	43,767
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	9,126	15,020
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	6,598	28,747
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	17,272
Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		17,272
Corporate debt securities | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		0
Corporate debt securities | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities		17,272
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	2,400	6,275
Commercial paper | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	2,400	7,274
Commercial paper | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Commercial paper | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	2,400	7,274
U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	4,198	4,201
U.S. government agency securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	4,198	4,201
U.S. government agency securities | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
U.S. government agency securities | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	4,198	4,201
Money market funds | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	9,126	15,020
Money market funds | Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	9,126	15,020
Money market funds | Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Money market funds	$ 0	$ 0

Goodwill (Details)

Goodwill (Details)	Sep. 30, 2017USD ($)
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill impairment	$ 0

Balance Sheet Details - Account

Balance Sheet Details - Accounts Receivable (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of accounts receivable, net
Accounts receivable	$ 45,630	$ 52,792
Allowance for doubtful accounts	(550)	(518)
Product return reserve	(853)	(938)
Accounts receivable, net	$ 44,227	$ 51,336

Balance Sheet Details - Invento

Balance Sheet Details - Inventory (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of inventory, net
Raw materials	$ 1,082	$ 1,827
Finished goods	35,239	42,718
Total inventory	$ 36,321	$ 44,545

Balance Sheet Details - Propert

Balance Sheet Details - Property and Equipment, net (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of property and equipment, net
Property and equipment, gross	$ 89,881	$ 83,615
Accumulated depreciation and amortization	(72,884)	(65,631)
Property and equipment, net	16,997	17,984
Test equipment
Summary of property and equipment, net
Property and equipment, gross	46,580	43,580
Computer equipment and software
Summary of property and equipment, net
Property and equipment, gross	33,652	30,306
Furniture and fixtures
Summary of property and equipment, net
Property and equipment, gross	2,890	2,831
Leasehold improvements
Summary of property and equipment, net
Property and equipment, gross	$ 6,759	$ 6,898

Balance Sheet Details - Accrued

Balance Sheet Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Summary of accrued liabilities
Accrued compensation and related benefits	$ 23,890	$ 19,541
Accrued professional and consulting fees	12,222	8,205
Accrued warranty and retrofit	8,454	12,214
Advance customer payments	5,211	20,726
Accrued excess and obsolete inventory at contract manufacturers	1,819	1,327
Accrued customer rebates	828	1,931
Accrued restructuring charges	195	0
Accrued other	6,782	5,771
Total accrued liabilities	$ 59,401	$ 69,715

Balance Sheet Details - Deferre

Balance Sheet Details - Deferred Revenue (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	$ 28,228	$ 27,854
Deferred revenue, noncurrent	21,173	20,237
Deferred revenue	49,401	48,091
Revenue Contract
Deferred Revenue Arrangement [Line Items]
Deferred revenue	3,400	20,300
Products and services
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	24,512	24,472
Deferred revenue, noncurrent	18	22
Extended warranty
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	3,716	3,382
Deferred revenue, noncurrent	$ 21,155	$ 20,215

Commitments and Contingencies -

Commitments and Contingencies - Textual (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Commitments and Contingencies [Line Items]
Outstanding purchase commitments	$ 62,600
Accrued excess and obsolete inventory at contract manufacturers	$ 1,819	$ 1,327
Warranty period	3 years
Minimum
Commitments and Contingencies [Line Items]
Warranty period	1 year
Maximum
Commitments and Contingencies [Line Items]
Warranty period	5 years

Commitments and Contingencies40

Commitments and Contingencies - Operating Leases (Details) - USD ($) $ in Thousands	Jan. 28, 2013	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Operating Leased Assets [Line Items]
Remainder of 2017		$ 756		$ 756
2,018		2,794		2,794
2,019		1,082		1,082
2,020		738		738
2,021		286		286
Thereafter		19		19
Future minimum payments due		5,675		5,675
Rent expense		$ 900	$ 900	$ 2,700	$ 2,600
Petaluma Lease
Operating Leased Assets [Line Items]
Proceeds from lease incentives	$ 1,200
Petaluma Lease Amendment
Operating Leased Assets [Line Items]
Proceeds from lease incentives	$ 400

Commitments and Contingencies41

Commitments and Contingencies - Product Warranty Activities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Product warranty activities [Roll Forward]
Balance at beginning of period	$ 9,265	$ 9,152	$ 12,214	$ 9,564
Provision for warranty and retrofit charged to cost of revenue	2,057	3,180	5,661	6,292
Utilization of reserve	(2,868)	(948)	(9,421)	(4,073)
Adjustments to pre-existing reserve	0	(11)	0	(410)
Balance at end of period	$ 8,454	$ 11,373	$ 8,454	$ 11,373

Net Income (Loss) Per Common 42

Net Income (Loss) Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Numerator:
Net income (loss)	$ (17,853)	$ 636	$ (70,166)	$ (15,919)
Denominator:
Weighted-average common shares outstanding used to compute basic net income (loss) per share (in shares)	50,336	48,773	49,960	48,578
Effect of dilutive common stock equivalents (in shares)	0	536	0	0
Weighted-average common shares outstanding used to compute diluted net income (loss) per share (in shares)	50,336	49,309	49,960	48,578
Net income (loss) per common share, basic (in dollars per share)	$ (0.35)	$ 0.01	$ (1.40)	$ (0.33)
Net income (loss) per common share, diluted (in dollars per share)	$ (0.35)	$ 0.01	$ (1.40)	$ (0.33)
Potentially dilutive shares, weighted average (in shares)	5,741	3,951	5,704	5,794

Stockholders' Equity (Details)

Stockholders' Equity (Details) $ / shares in Units, $ in Thousands	May 17, 2017periodshares	Sep. 30, 2017USD ($)Plan$ / sharesshares	Sep. 30, 2017USD ($)Plan$ / sharesshares	Sep. 24, 2016USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of equity incentive plans | Plan		2	2
Stock options granted (in shares)		1,565,000	1,565,000
Weighted-average grant date fair value (in dollars per share) | $ / shares		$ 3.45	$ 3.45
Stock options exercised (in shares)		0	5,000
Weighted-average exercise price per share, stock options (in dollars per share) | $ / shares			$ 5.99
Unrecognized stock-based compensation expense, stock options | $		$ 3,400	$ 3,400
Weighted-average amortization period			2 years 3 months 18 days
Taxes paid for awards vested under equity incentive plans | $			$ 2,743	$ 1,787
Performance Based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options granted (in shares)		1,165,000	1,165,000
Weighted-average grant date fair value (in dollars per share) | $ / shares		$ 3.43	$ 3.43
Performance Based Stock Options | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			1 year
Performance Based Stock Options | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			3 years
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average amortization period			2 years 2 months 12 days
Awards granted (in shares)		92,266	505,236
Weighted-average grant date fair value per share (in dollars per share) | $ / shares		$ 6.34	$ 6.75
Awards vested (in shares)		107,107	670,095
Taxes paid for awards vested under equity incentive plans | $		$ 100	$ 1,800
Unrecognized stock-based compensation expense | $		10,200	$ 10,200
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average amortization period			1 month 14 days
Unrecognized stock-based compensation expense | $		$ 200	$ 200
ESPP, maximum employee payroll deduction percentage		15.00%	15.00%
ESPP, maximum number of shares per employee (in shares)			2,000
ESPP, discounted purchase price percentage			85.00%
ESPP, shares purchased		0	119,011
Offering period			6 months
Shares available for issuance under the ESPP (in shares)		3,000,217	3,000,217
Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average amortization period			10 months 9 days
Awards vested (in shares)		0	325,000
Shares of stock issued upon conversion of units (in shares)			195,656
Taxes paid for awards vested under equity incentive plans | $			$ 900
Unrecognized stock-based compensation expense | $		$ 300	$ 300
Performance Restricted Stock Units | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			1 year
Performance Restricted Stock Units | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Performance period			2 years
Period one | Performance Based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Period one | Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			50.00%
Period two | Performance Based Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			6.25%
Period two | Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Period three | Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
2017 Nonqualified Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized stock-based compensation expense, stock options | $		$ 1,200	$ 1,200
Weighted-average amortization period			1 year 3 months
Maximum contribution percent (up to 25%)	25.00%
Number of offering periods | period	2
Offering period	6 months
Number of shares authorized	1,000,000
Number of shares authorized per purchase period	500,000

Accumulated Other Comprehensi44

Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period			$ 212,964
Other comprehensive income (loss)	$ 120	$ (96)	312	$ (31)
Balance at end of period	150,383		150,383
Unrealized Gains and Losses on Available-for-Sale Marketable Securities
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(7)	12	(6)	(94)
Other comprehensive income (loss)	4	(9)	3	97
Balance at end of period	(3)	3	(3)	3
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(457)	(142)	(650)	(101)
Other comprehensive income (loss)	116	(87)	309	(128)
Balance at end of period	(341)	(229)	(341)	(229)
Total
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(464)	(130)	(656)	(195)
Balance at end of period	$ (344)	$ (226)	$ (344)	$ (226)

Credit Facility (Details)

Credit Facility (Details) - USD ($)	Aug. 07, 2017	Sep. 30, 2017	Jul. 29, 2013
Debt Instrument [Line Items]
Maximum borrowing capacity			$ 50,000,000
Silicon Valley Bank
Debt Instrument [Line Items]
Maximum amount outstanding during period	$ 30,000,000
Outstanding revolving loans		$ 30,000,000
Silicon Valley Bank | Prime Rate | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	0.50%
Silicon Valley Bank | Prime Rate | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	1.50%
Silicon Valley Bank | LIBOR | Minimum
Debt Instrument [Line Items]
Basis spread on variable rate	2.00%
Silicon Valley Bank | LIBOR | Maximum
Debt Instrument [Line Items]
Basis spread on variable rate	3.00%
Silicon Valley Bank | Letter of Credit
Debt Instrument [Line Items]
Maximum borrowing capacity	$ 10,000,000
Silicon Valley Bank | Non Formula Revolver
Debt Instrument [Line Items]
Maximum borrowing capacity	5,000,000
Silicon Valley Bank | Revolving Credit Facility
Debt Instrument [Line Items]
Maximum borrowing capacity	30,000,000
Early termination fees, amount	$ 300,000

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 225	$ 209	$ 1,075	$ 454
Effective tax rate	(1.30%)	24.70%	(1.60%)	(2.90%)

Restructuring Charges (Details)

Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 24, 2016	Sep. 30, 2017	Sep. 24, 2016
Restructuring Reserve [Roll Forward]
Restructuring charges for the period	$ 612	$ 0	$ 2,268	$ 0
Expected restructuring charges	4,000		4,000
Expected additional charges	1,700		1,700
Employee Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	600		0
Restructuring charges for the period	600		2,268
Cash payments	(1,017)		(2,073)
Liability at end of period	$ 195		$ 195