Calix (CALX) 10-Q 10 Aug 17 2017 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jul. 01, 2017	Aug. 03, 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	Jul. 1, 2017
Amendment Flag	false
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q2
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		50,307,864

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 37,294	$ 50,359
Marketable securities	12,915	27,748
Accounts receivable, net	53,392	51,336
Inventory	39,572	44,545
Deferred cost of revenue	40,094	34,763
Prepaid expenses and other current assets	11,112	10,571
Total current assets	194,379	219,322
Property and equipment, net	17,959	17,984
Goodwill	116,175	116,175
Intangible assets, net	0	813
Other assets	811	1,181
Total assets	329,324	355,475
Current liabilities:
Accounts payable	27,840	23,827
Accrued liabilities	72,662	69,715
Deferred revenue	41,847	27,854
Total current liabilities	142,349	121,396
Long-term portion of deferred revenue	21,104	20,237
Other long-term liabilities	638	878
Total liabilities	164,091	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 July 1, 2017 and December 31, 2016	0	0
Common stock, $0.025 par value; 100,000 shares authorized; 55,605 shares issued and 50,275 shares outstanding as of July 1, 2017, and 54,722 shares issued and 49,392 shares outstanding as of December 31, 2016	1,390	1,368
Additional paid-in capital	840,931	836,563
Accumulated other comprehensive loss	(464)	(656)
Accumulated deficit	(636,638)	(584,325)
Treasury stock, 5,330 shares as of July 1, 2017 and December 31, 2016	(39,986)	(39,986)
Total stockholders’ equity	165,233	212,964
Total liabilities and stockholders’ equity	$ 329,324	$ 355,475

Condensed Consolidated Balance3

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jul. 01, 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	55,605,000	54,722,000
Common stock, shares outstanding	50,275,000	49,392,000
Treasury stock, shares	5,330,000	5,330,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		6 Months Ended
		Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Revenue:
Products		$ 107,348	$ 100,144	$ 198,953	$ 191,824
Services		18,775	7,281	44,688	13,976
Total revenue		126,123	107,425	243,641	205,800
Cost of revenue:
Products	[1]	58,299	51,501	115,672	99,194
Services	[1]	24,501	5,918	50,269	11,118
Total cost of revenue		82,800	57,419	165,941	110,312
Gross profit		43,323	50,006	77,700	95,488
Operating expenses:
Research and development	[1]	32,950	25,033	66,758	47,806
Sales and marketing	[1]	18,429	19,213	40,858	38,275
General and administrative	[1]	9,701	11,641	19,958	24,325
Amortization of intangible assets		0	0	0	1,701
Restructuring charges		957	0	1,656	0
Total operating expenses		62,037	55,887	129,230	112,107
Loss from operations		(18,714)	(5,881)	(51,530)	(16,619)
Interest and other income (expense), net:
Interest income, net		54	97	148	194
Other income (expense), net		(151)	82	(81)	115
Loss before provision for income taxes		(18,811)	(5,702)	(51,463)	(16,310)
Provision for income taxes		177	124	850	245
Net loss		$ (18,988)	$ (5,826)	$ (52,313)	$ (16,555)
Net loss per common share, basic and diluted (in dollars per share)		$ (0.38)	$ (0.12)	$ (1.05)	$ (0.34)
Weighted-average number of shares used to compute net loss per common share:
Basic and diluted (in shares)		50,019	48,371	49,772	48,478
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on available-for-sale marketable securities, net		$ 3	$ 41	$ (1)	$ 106
Foreign currency translation adjustments, net		132	(23)	193	(41)
Total other comprehensive income, net of tax		135	18	192	65
Comprehensive loss		$ (18,853)	$ (5,808)	$ (52,121)	$ (16,490)
[1]	Includes stock-based compensation as follows: Three Months Ended July 1, 2017 and June 25, 2016; Cost of revenue: Products - $93, $128, 209, 218; Services - $75, $55, 126, 92; Research and development - $1,122, $1,099, 2,448, 2,146; Sales and marketing - $654, $840, 1,765, 1,662; General administrative - $831, $846, 1,762, 1,571;

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Loss (Unaudited) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Products
Stock-based compensation	$ 96	$ 128	$ 212	$ 218
Services
Stock-based compensation	75	55	131	92
Research and development
Stock-based compensation	1,122	1,099	2,448	2,146
Sales and marketing
Stock-based compensation	654	840	1,765	1,662
General and administrative
Stock-based compensation	$ 831	$ 846	$ 1,762	$ 1,571

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016
Operating activities:
Net loss	$ (52,313)	$ (16,555)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	4,929	4,131
Loss on retirement of property and equipment	80	0
Amortization of intangible assets	813	4,178
Amortization of premium (discount) related to available-for-sale securities	(3)	233
Stock-based compensation	6,318	5,689
Changes in operating assets and liabilities:
Accounts receivable, net	(2,056)	(1,963)
Inventory	4,973	6,906
Deferred cost of revenue	(5,331)	(1,894)
Prepaid expenses and other assets	(156)	1,394
Accounts payable	3,731	(5,859)
Accrued liabilities	2,962	9,012
Deferred revenue	14,860	323
Other long-term liabilities	(241)	(207)
Net cash provided by (used in) operating activities	(21,434)	5,388
Investing activities:
Purchases of property and equipment	(4,715)	(3,078)
Purchases of marketable securities	(8,732)	0
Sales of marketable securities	5,051	0
Maturities of marketable securities	18,516	11,670
Net cash provided by investing activities	10,120	8,592
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	(2,630)	(1,547)
Net cash used in financing activities	(1,928)	(11,437)
Effect of exchange rate changes on cash and cash equivalents	177	(124)
Net increase (decrease) in cash and cash equivalents	(13,065)	2,419
Cash and cash equivalents at beginning of period	50,359	23,626
Cash and cash equivalents at end of period	$ 37,294	$ 26,045

Company and Basis of Presentati

Company and Basis of Presentation	6 Months Ended
	Jul. 01, 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, 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 fiscal 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 1st and ends on December 31st. Quarterly periods are based on a 4-4-5 fiscal calendar with the first, second and third fiscal quarters ending on the 13th Saturday of each fiscal period. As a result, the Company had five more days in the six months ended July 1, 2017 than in the six months ended June 25, 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 six months ended July 1, 2017 represents more than 10% of its total revenue; hence, the revenue derived from services along with its associated cost of revenue are presented separately in the accompanying Condensed Consolidated Statements of Comprehensive Loss. Services include professional services, software support services for access systems, extended warranty and training services. Accordingly, revenue and cost of revenue for the three and six months ended June 25, 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 loss.

Significant Accounting Policies

Significant Accounting Policies	6 Months Ended
	Jul. 01, 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 six months ended July 1, 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 fiscal 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 fiscal 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 loss from operations or net 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 July 1, 2017 and two customers that each accounted for more than 10% of its total revenue for the six months ended July 1, 2017 . These two customers each accounted for more than 10% of the Company’s total revenue for the three and six months ended June 25, 2016 . These two customers together represented 34% and 44% of the Company’s total revenue for the three and six months ended July 1, 2017 , respectively, and 35% and 32% for the three and six months ended June 25, 2016 , respectively. Each of these two customers represented more than 10% of the Company’s accounts receivable as of July 1, 2017 and December 31, 2016 .

Cash, Cash Equivalents and Mark

Cash, Cash Equivalents and Marketable Securities	6 Months Ended
	Jul. 01, 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 July 1, 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): July 1, December 31, Cash and cash equivalents: Cash $ 34,534 $ 34,340 Money market funds 2,760 15,020 Commercial paper — 999 Total cash and cash equivalents 37,294 50,359 Marketable securities: Corporate debt securities 6,125 17,272 Commercial paper 2,594 6,275 U.S. government agency securities 4,196 4,201 Total marketable securities 12,915 27,748 $ 50,209 $ 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 July 1, 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 Corporate debt securities $ 6,128 $ — $ (3 ) $ 6,125 Commercial paper 2,594 — — 2,594 U.S. government agency securities 4,200 — (4 ) 4,196 $ 12,922 $ — $ (7 ) $ 12,915 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	6 Months Ended
	Jul. 01, 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 July 1, 2017 and December 31, 2016 , based on the three-tier fair value hierarchy (in thousands): As of July 1, 2017 Level 1 Level 2 Total Money market funds $ 2,760 $ — $ 2,760 Corporate debt securities — 6,125 6,125 Commercial paper — 2,594 2,594 U.S. government agency securities — 4,196 4,196 $ 2,760 $ 12,915 $ 15,675 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 six months ended July 1, 2017 and June 25, 2016 .

Goodwill and Intangible Assets

Goodwill and Intangible Assets	6 Months Ended
	Jul. 01, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	Goodwill and Intangible Assets 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. Intangible Assets Intangible assets are carried at cost, less accumulated amortization. The details of intangible assets as of July 1, 2017 and December 31, 2016 are disclosed in the following table (in thousands): July 1, 2017 December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net Core developed technology $ 68,964 $ (68,964 ) $ — $ 68,964 $ (68,151 ) $ 813 Customer relationships 54,740 (54,740 ) — 54,740 (54,740 ) — $ 123,704 $ (123,704 ) $ — $ 123,704 $ (122,891 ) $ 813 All intangible assets were fully amortized at April 1, 2017. Amortization expense in the periods as indicated were recognized as follows (in thousands): Three Months Ended Six Months Ended July 1, June 25, July 1, June 25, Cost of products revenue $ — $ 814 $ 813 $ 2,477 Operating expenses — — — 1,701 $ — $ 814 $ 813 $ 4,178

Balance Sheet Details

Balance Sheet Details	6 Months Ended
	Jul. 01, 2017
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	Balance Sheet Details Accounts receivable, net consisted of the following (in thousands): July 1, December 31, Accounts receivable $ 55,390 $ 52,792 Allowance for doubtful accounts (450 ) (518 ) Product return reserve (1,548 ) (938 ) $ 53,392 $ 51,336 Inventory consisted of the following (in thousands): July 1, December 31, Raw materials $ 1,028 $ 1,827 Finished goods 38,544 42,718 $ 39,572 $ 44,545 Property and equipment, net consisted of the following (in thousands): July 1, December 31, Test equipment $ 45,559 $ 43,580 Computer equipment and software 32,833 30,306 Furniture and fixtures 2,881 2,831 Leasehold improvements 6,893 6,898 Total 88,166 83,615 Accumulated depreciation and amortization (70,207 ) (65,631 ) $ 17,959 $ 17,984 Accrued liabilities consisted of the following (in thousands): July 1, December 31, Advance customer payments $ 20,199 $ 20,726 Accrued compensation and related benefits 19,007 19,541 Accrued professional and consulting fees 14,215 8,205 Accrued warranty and retrofit 9,265 12,214 Accrued excess and obsolete inventory at contract manufacturers 1,979 1,327 Accrued customer rebates 717 1,931 Accrued restructuring charges 600 — Accrued other 6,680 5,771 $ 72,662 $ 69,715 Advance customer payments as of July 1, 2017 and December 31, 2016 primarily included $19.4 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 network improvement projects for a customer. Deferred revenue consisted of the following (in thousands): July 1, December 31, Current: Products and services $ 38,454 $ 24,472 Extended warranty 3,393 3,382 41,847 27,854 Long-term: Products and services 26 22 Extended warranty 21,078 20,215 21,104 20,237 $ 62,951 $ 48,091 Deferred cost of revenue consisted of costs incurred for products and services for which revenues have been deferred or not yet earned.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jul. 01, 2017
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Commitments The Company’s principal commitments consist of obligations under operating leases for office space and non-cancelable outstanding purchase obligations. These commitments as of December 31, 2016 are disclosed in the Company’s Annual Report on Form 10-K, and have not changed materially during the six months ended July 1, 2017 . 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 Six Months Ended July 1, June 25, July 1, June 25, Balance at beginning of period $ 10,778 $ 9,152 $ 12,214 $ 9,564 Provision for warranty and retrofit charged to cost of revenue 1,743 2,532 3,605 3,112 Utilization of reserve (3,256 ) (1,485 ) (6,554 ) (2,104 ) Adjustments to pre-existing reserve — (25 ) — (398 ) Balance at end of period $ 9,265 $ 10,174 $ 9,265 $ 10,174 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 Loss per Common Share

Net Loss per Common Share	6 Months Ended
	Jul. 01, 2017
Earnings Per Share [Abstract]
Net Loss per Common Share	Net Loss Per Common Share The following table sets forth the computation of basic and diluted net loss per common share for the periods indicated (in thousands, except per share data): Three Months Ended Six Months Ended July 1, June 25, July 1, June 25, Numerator: Net loss $ (18,988 ) $ (5,826 ) $ (52,313 ) $ (16,555 ) Denominator: Weighted-average common shares outstanding 50,019 48,371 49,772 48,478 Basic and diluted net loss per common share $ (0.38 ) $ (0.12 ) $ (1.05 ) $ (0.34 ) Potentially dilutive shares, weighted average 5,225 5,733 5,685 5,620 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	6 Months Ended
	Jul. 01, 2017
Stockholders' Equity Note [Abstract]
Stockholders' Equity	Stockholders’ Equity Equity Incentive Plans 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 six months ended July 1, 2017 , no stock options were granted. During the three months ended July 1, 2017 , 3,000 shares of stock options were exercised at a weighted-average exercise price of $5.62 per share. During the six months ended July 1, 2017 , 5,000 shares of stock options were exercised at a weighted-average exercise price of $5.99 per share. As of July 1, 2017 , unrecognized stock-based compensation expense of $2.5 million related to stock options, net of estimated forfeitures, is expected to be recognized over a weighted-average period of 2.8 years. Restricted Stock Units During the three months ended July 1, 2017 , 209,870 shares of RSUs were granted with a weighted-average grant date fair value of $6.70 per share. During the six months ended July 1, 2017 , 412,970 shares of RSUs were granted with a weighted-average grant date fair value of $6.85 per share. During the three months ended July 1, 2017 , 510,827 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 six months ended July 1, 2017 , 562,988 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 $1.5 million were remitted to the relevant taxing authorities during the three months ended July 1, 2017 . Taxes withheld from employees of $1.7 million were remitted to the relevant taxing authorities during the six months ended July 1, 2017 . As of July 1, 2017 , unrecognized stock-based compensation expense of $11.6 million related to RSUs, net of estimated forfeitures, was expected to be recognized over a weighted-average period of 2.4 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 July 1, 2017 , 25,000 shares of PRSUs vested and were converted into 15,604 shares of common stock, net of shares withheld for statutory income tax purposes. During the six months ended July 1, 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 $0.1 million were remitted to the relevant taxing authorities during the three months ended July 1, 2017 . Taxes withheld from employees of $0.9 million were remitted to the relevant taxing authorities during the six months ended July 1, 2017 . As of July 1, 2017 , unrecognized stock-based compensation expense of $0.4 million related to PRSUs, net of estimated forfeitures, is expected to be recognized over a weighted-average period of 1.1 years. 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 July 1, 2017 , there were 3,000,217 shares available for issuance under the Restated ESPP. During the three and six months ended July 1, 2017 , 119,011 shares were purchased under the Restated ESPP. As of July 1, 2017 , unrecognized stock-based compensation expense of $0.7 million related to the Restated ESPP is expected to be recognized over a remaining service period of 4.5 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. Stock-Based Compensation Expense Stock-based compensation expense associated with stock options, RSUs, PRSUs and purchase rights under the 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 Company values RSUs at the 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. Compensation expense 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 fair value of PRSUs with a market condition is estimated on the date of award, using a Monte Carlo simulation model to estimate the TSR 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	6 Months Ended
	Jul. 01, 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 July 1, 2017 June 25, 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 $ (10 ) $ (589 ) $ (599 ) $ (29 ) $ (119 ) $ (148 ) Other comprehensive income (loss) 3 132 135 41 (23 ) 18 Balance at end of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 ) Six Months Ended July 1, 2017 June 25, 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) (1 ) 193 192 106 (41 ) 65 Balance at end of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 ) 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 Loss.

Credit Facility

Credit Facility	6 Months Ended
	Jul. 01, 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). The Company had determined that as of July 1, 2017 , no funds were available for borrowing under the Credit Agreement based on the Company’s consolidated leverage ratios. In August 2017, the Company entered into a loan and security agreement (the “Loan Agreement”) with Silicon Valley Bank (“SVB”). In connection with the Loan Agreement, the Company terminated the Credit Agreement. (See Note 14, Subsequent Event .)

Income Taxes

Income Taxes	6 Months Ended
	Jul. 01, 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 Six Months Ended July 1, June 25, July 1, June 25, Provision for income taxes $ 177 $ 124 $ 850 $ 245 Effective tax rate (0.9 )% (2.2 )% (1.7 )% (1.5 )% The income tax provision for the three and six months ended July 1, 2017 and June 25, 2016 consisted primarily of foreign income taxes. The effective tax rate for the three and six months ended July 1, 2017 and June 25, 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 six months ended July 1, 2017 and June 25, 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	6 Months Ended
	Jul. 01, 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 innovative software defined access systems and software, 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 approximately $1.0 million and $1.7 million of restructuring charges for the three and six months ended July 1, 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 Loss. The following table summarizes the activities related to the restructuring charges pursuant to the above restructuring plan (in thousands): Three Months Ended July 1, 2017 Six Months Ended July 1, 2017 Liability at beginning of period $ 699 $ — Restructuring charges for the period 957 1,656 Cash payments (1,056 ) (1,056 ) Liability at end of period $ 600 $ 600 The Company currently estimates that this plan will result in pre-tax restructuring charges totaling up to $6.8 million with approximately up to $5.1 million of additional charges expected to be recognized during the rest of fiscal 2017. These charges are primarily cash-based.

Subsequent Event

Subsequent Event	6 Months Ended
	Jul. 01, 2017
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event In August 2017, the Company entered into the Loan Agreement 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. 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.

Significant Accounting Polici21

Significant Accounting Policies (Policies)	6 Months Ended
	Jul. 01, 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 fiscal 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 fiscal 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 loss from operations or net 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 Ma22

Cash, Cash Equivalents and Marketable Securities (Tables)	6 Months Ended
	Jul. 01, 2017
Cash and Cash Equivalents [Abstract]
Summary of cash and cash equivalents	Cash, cash equivalents and marketable securities consisted of the following (in thousands): July 1, December 31, Cash and cash equivalents: Cash $ 34,534 $ 34,340 Money market funds 2,760 15,020 Commercial paper — 999 Total cash and cash equivalents 37,294 50,359 Marketable securities: Corporate debt securities 6,125 17,272 Commercial paper 2,594 6,275 U.S. government agency securities 4,196 4,201 Total marketable securities 12,915 27,748 $ 50,209 $ 78,107
Amortized cost and fair value of marketable securities	As of July 1, 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 Corporate debt securities $ 6,128 $ — $ (3 ) $ 6,125 Commercial paper 2,594 — — 2,594 U.S. government agency securities 4,200 — (4 ) 4,196 $ 12,922 $ — $ (7 ) $ 12,915 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)	6 Months Ended
	Jul. 01, 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 July 1, 2017 and December 31, 2016 , based on the three-tier fair value hierarchy (in thousands): As of July 1, 2017 Level 1 Level 2 Total Money market funds $ 2,760 $ — $ 2,760 Corporate debt securities — 6,125 6,125 Commercial paper — 2,594 2,594 U.S. government agency securities — 4,196 4,196 $ 2,760 $ 12,915 $ 15,675 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

Goodwill and Intangible Assets

Goodwill and Intangible Assets (Tables)	6 Months Ended
	Jul. 01, 2017
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of intangible assets	Intangible assets are carried at cost, less accumulated amortization. The details of intangible assets as of July 1, 2017 and December 31, 2016 are disclosed in the following table (in thousands): July 1, 2017 December 31, 2016 Gross Carrying Amount Accumulated Amortization Net Gross Carrying Amount Accumulated Amortization Net Core developed technology $ 68,964 $ (68,964 ) $ — $ 68,964 $ (68,151 ) $ 813 Customer relationships 54,740 (54,740 ) — 54,740 (54,740 ) — $ 123,704 $ (123,704 ) $ — $ 123,704 $ (122,891 ) $ 813
Amortization expense, income statement location	Amortization expense in the periods as indicated were recognized as follows (in thousands): Three Months Ended Six Months Ended July 1, June 25, July 1, June 25, Cost of products revenue $ — $ 814 $ 813 $ 2,477 Operating expenses — — — 1,701 $ — $ 814 $ 813 $ 4,178

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	6 Months Ended
	Jul. 01, 2017
Balance Sheet Related Disclosures [Abstract]
Summary of accounts receivable, net	Accounts receivable, net consisted of the following (in thousands): July 1, December 31, Accounts receivable $ 55,390 $ 52,792 Allowance for doubtful accounts (450 ) (518 ) Product return reserve (1,548 ) (938 ) $ 53,392 $ 51,336
Summary of inventory	Inventory consisted of the following (in thousands): July 1, December 31, Raw materials $ 1,028 $ 1,827 Finished goods 38,544 42,718 $ 39,572 $ 44,545
Summary of property and equipment, net	Property and equipment, net consisted of the following (in thousands): July 1, December 31, Test equipment $ 45,559 $ 43,580 Computer equipment and software 32,833 30,306 Furniture and fixtures 2,881 2,831 Leasehold improvements 6,893 6,898 Total 88,166 83,615 Accumulated depreciation and amortization (70,207 ) (65,631 ) $ 17,959 $ 17,984
Summary of accrued liabilities	Accrued liabilities consisted of the following (in thousands): July 1, December 31, Advance customer payments $ 20,199 $ 20,726 Accrued compensation and related benefits 19,007 19,541 Accrued professional and consulting fees 14,215 8,205 Accrued warranty and retrofit 9,265 12,214 Accrued excess and obsolete inventory at contract manufacturers 1,979 1,327 Accrued customer rebates 717 1,931 Accrued restructuring charges 600 — Accrued other 6,680 5,771 $ 72,662 $ 69,715
Summary of deferred revenue	Deferred revenue consisted of the following (in thousands): July 1, December 31, Current: Products and services $ 38,454 $ 24,472 Extended warranty 3,393 3,382 41,847 27,854 Long-term: Products and services 26 22 Extended warranty 21,078 20,215 21,104 20,237 $ 62,951 $ 48,091

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jul. 01, 2017
Commitments and Contingencies Disclosure [Abstract]
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 Six Months Ended July 1, June 25, July 1, June 25, Balance at beginning of period $ 10,778 $ 9,152 $ 12,214 $ 9,564 Provision for warranty and retrofit charged to cost of revenue 1,743 2,532 3,605 3,112 Utilization of reserve (3,256 ) (1,485 ) (6,554 ) (2,104 ) Adjustments to pre-existing reserve — (25 ) — (398 ) Balance at end of period $ 9,265 $ 10,174 $ 9,265 $ 10,174

Net Loss per Common Share (Tabl

Net Loss per Common Share (Tables)	6 Months Ended
	Jul. 01, 2017
Earnings Per Share [Abstract]
Schedule of net loss per share	The following table sets forth the computation of basic and diluted net loss per common share for the periods indicated (in thousands, except per share data): Three Months Ended Six Months Ended July 1, June 25, July 1, June 25, Numerator: Net loss $ (18,988 ) $ (5,826 ) $ (52,313 ) $ (16,555 ) Denominator: Weighted-average common shares outstanding 50,019 48,371 49,772 48,478 Basic and diluted net loss per common share $ (0.38 ) $ (0.12 ) $ (1.05 ) $ (0.34 ) Potentially dilutive shares, weighted average 5,225 5,733 5,685 5,620

Accumulated Other Comprehensi28

Accumulated Other Comprehensive Loss (Tables)	6 Months Ended
	Jul. 01, 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 July 1, 2017 June 25, 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 $ (10 ) $ (589 ) $ (599 ) $ (29 ) $ (119 ) $ (148 ) Other comprehensive income (loss) 3 132 135 41 (23 ) 18 Balance at end of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 ) Six Months Ended July 1, 2017 June 25, 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) (1 ) 193 192 106 (41 ) 65 Balance at end of period $ (7 ) $ (457 ) $ (464 ) $ 12 $ (142 ) $ (130 )

Income Taxes (Tables)

Income Taxes (Tables)	6 Months Ended
	Jul. 01, 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 Six Months Ended July 1, June 25, July 1, June 25, Provision for income taxes $ 177 $ 124 $ 850 $ 245 Effective tax rate (0.9 )% (2.2 )% (1.7 )% (1.5 )%

Restructuring Charges (Tables)

Restructuring Charges (Tables)	6 Months Ended
	Jul. 01, 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 July 1, 2017 Six Months Ended July 1, 2017 Liability at beginning of period $ 699 $ — Restructuring charges for the period 957 1,656 Cash payments (1,056 ) (1,056 ) Liability at end of period $ 600 $ 600

Significant Accounting Polici31

Significant Accounting Policies (Details)	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Largest Two Customers | Customer Concentration Risk | Revenue
Concentration Risk [Line Items]
Concentration risk, percentage	34.00%	35.00%	44.00%	32.00%

Cash, Cash Equivalents and Ma32

Cash, Cash Equivalents and Marketable Securities (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016	Jun. 25, 2016	Dec. 31, 2015
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 37,294	$ 50,359	$ 26,045	$ 23,626
Marketable securities	12,915	27,748
Total cash, cash equivalents and marketable securities	50,209	78,107
Corporate debt securities
Cash and Cash Equivalents [Line Items]
Marketable securities	6,125	17,272
Commercial paper
Cash and Cash Equivalents [Line Items]
Marketable securities	2,594	6,275
U.S. government agency securities
Cash and Cash Equivalents [Line Items]
Marketable securities	4,196	4,201
Cash
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	34,534	34,340
Money market funds
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	2,760	15,020
Commercial paper
Cash and Cash Equivalents [Line Items]
Cash and cash equivalents	$ 0	$ 999

Cash, Cash Equivalents and Ma33

Cash, Cash Equivalents and Marketable Securities - Amortized Cost and Fair Value (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 12,922	$ 27,754
Gross Unrealized Gains	0	2
Gross Unrealized Losses	(7)	(8)
Fair Value	12,915	27,748
Corporate debt securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	6,128	17,279
Gross Unrealized Gains	0	1
Gross Unrealized Losses	(3)	(8)
Fair Value	6,125	17,272
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,594	6,275
Gross Unrealized Gains	0	0
Gross Unrealized Losses	0	0
Fair Value	2,594	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	(4)	0
Fair Value	$ 4,196	$ 4,201

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	$ 12,915	$ 27,748
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	15,675	43,767
Fair Value, Measurements, Recurring | Level 1
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	2,760	15,020
Fair Value, Measurements, Recurring | Level 2
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total	12,915	28,747
Corporate debt securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	6,125	17,272
Corporate debt securities | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	6,125	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	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	6,125	17,272
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	2,594	6,275
Commercial paper | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	2,594	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	2,594	7,274
U.S. government agency securities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	4,196	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	4,196	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	4,196	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	2,760	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	2,760	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 and Intangible Asset35

Goodwill and Intangible Assets - Schedule of Intangible Assets (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 123,704	$ 123,704
Accumulated Amortization	(123,704)	(122,891)
Net	0	813
Core developed technology
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	68,964	68,964
Accumulated Amortization	(68,964)	(68,151)
Net	0	813
Customer relationships
Acquired Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	54,740	54,740
Accumulated Amortization	(54,740)	(54,740)
Net	$ 0	$ 0

Goodwill and Intangible Asset36

Goodwill and Intangible Assets - Amortization Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0	$ 814	$ 813	$ 4,178
Cost of products revenue
Finite-Lived Intangible Assets [Line Items]
Amortization expense	0	814	813	2,477
Operating expenses
Finite-Lived Intangible Assets [Line Items]
Amortization expense	$ 0	$ 0	$ 0	$ 1,701

Balance Sheet Details - Account

Balance Sheet Details - Accounts Receivable (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Summary of accounts receivable, net
Accounts receivable	$ 55,390	$ 52,792
Allowance for doubtful accounts	(450)	(518)
Product return reserve	(1,548)	(938)
Accounts receivable, net	$ 53,392	$ 51,336

Balance Sheet Details - Invento

Balance Sheet Details - Inventory (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Summary of inventory, net
Raw materials	$ 1,028	$ 1,827
Finished goods	38,544	42,718
Total inventory	$ 39,572	$ 44,545

Balance Sheet Details - Propert

Balance Sheet Details - Property and Equipment, net (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Summary of property and equipment, net
Property and equipment, gross	$ 88,166	$ 83,615
Accumulated depreciation and amortization	(70,207)	(65,631)
Property and equipment, net	17,959	17,984
Test equipment
Summary of property and equipment, net
Property and equipment, gross	45,559	43,580
Computer equipment and software
Summary of property and equipment, net
Property and equipment, gross	32,833	30,306
Furniture and fixtures
Summary of property and equipment, net
Property and equipment, gross	2,881	2,831
Leasehold improvements
Summary of property and equipment, net
Property and equipment, gross	$ 6,893	$ 6,898

Balance Sheet Details - Accrued

Balance Sheet Details - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Summary of accrued liabilities
Advance customer payments	$ 20,199	$ 20,726
Accrued compensation and related benefits	19,007	19,541
Accrued professional and consulting fees	14,215	8,205
Accrued warranty and retrofit	9,265	12,214
Accrued excess and obsolete inventory at contract manufacturers	1,979	1,327
Accrued customer rebates	717	1,931
Accrued restructuring charges	600	0
Accrued other	6,680	5,771
Total accrued liabilities	$ 72,662	$ 69,715

Balance Sheet Details - Deferre

Balance Sheet Details - Deferred Revenue (Details) - USD ($) $ in Thousands	Jul. 01, 2017	Dec. 31, 2016
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	$ 41,847	$ 27,854
Deferred revenue, noncurrent	21,104	20,237
Deferred revenue	62,951	48,091
Revenue Contract
Deferred Revenue Arrangement [Line Items]
Deferred revenue	19,400	20,300
Products and services
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	38,454	24,472
Deferred revenue, noncurrent	26	22
Extended warranty
Deferred Revenue Arrangement [Line Items]
Deferred revenue, current	3,393	3,382
Deferred revenue, noncurrent	$ 21,078	$ 20,215

Commitments and Contingencies -

Commitments and Contingencies - Textual (Details)	6 Months Ended
	Jul. 01, 2017
Commitments and Contingencies [Line Items]
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 Contingencies43

Commitments and Contingencies - Product Warranty Activities (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Product warranty activities [Roll Forward]
Balance at beginning of period	$ 10,778	$ 9,152	$ 12,214	$ 9,564
Provision for warranty and retrofit charged to cost of revenue	1,743	2,532	3,605	3,112
Utilization of reserve	(3,256)	(1,485)	(6,554)	(2,104)
Adjustments to pre-existing reserve	0	(25)	0	(398)
Balance at end of period	$ 9,265	$ 10,174	$ 9,265	$ 10,174

Net Loss per Common Share (Deta

Net Loss per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Numerator:
Net loss	$ (18,988)	$ (5,826)	$ (52,313)	$ (16,555)
Denominator:
Weighted-average common shares outstanding (in shares)	50,019	48,371	49,772	48,478
Basic and diluted net loss per common share (in dollars per share)	$ (0.38)	$ (0.12)	$ (1.05)	$ (0.34)
Potentially dilutive shares, weighted average (in shares)	5,225	5,733	5,685	5,620

Stockholders' Equity - Textual

Stockholders' Equity - Textual (Details) $ / shares in Units, $ in Thousands	May 17, 2017periodshares	Jul. 01, 2017USD ($)Plan$ / sharesshares	Jul. 01, 2017USD ($)Plan$ / sharesshares	Jun. 25, 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)		0	0
Stock options exercised (in shares)		3,000	5,000
Weighted-average exercise price per share, stock options (in dollars per share) | $ / shares		$ 5.62	$ 5.99
Unrecognized stock-based compensation expense, stock options | $		$ 2,500	$ 2,500
Weighted-average amortization period			2 years 9 months 15 days
Taxes paid for awards vested under equity incentive plans | $			$ 2,630	$ 1,547
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average amortization period			2 years 4 months 17 days
Awards granted (in shares)		209,870	412,970
Weighted-average grant date fair value per share (in dollars per share) | $ / shares		$ 6.70	$ 6.85
Awards vested (in shares)		510,827	562,988
Taxes paid for awards vested under equity incentive plans | $		$ 1,500	$ 1,700
Unrecognized stock-based compensation expense | $		11,600	$ 11,600
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted-average amortization period			4 months 15 days
Unrecognized stock-based compensation expense | $		$ 700	$ 700
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		119,011	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			1 year 1 month 7 days
Awards vested (in shares)		25,000	325,000
Shares of stock issued upon conversion of units (in shares)		15,604	195,656
Taxes paid for awards vested under equity incentive plans | $		$ 100	$ 900
Unrecognized stock-based compensation expense | $		$ 400	$ 400
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 - February 2017 | Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			50.00%
Period two - February 2018 | Performance Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage			25.00%
Period three - February 2019 | 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]
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 Comprehensi46

Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period			$ 212,964
Other comprehensive income (loss)	$ 135	$ 18	192	$ 65
Balance at end of period	165,233		165,233
Unrealized Gains and Losses on Available-for-Sale Marketable Securities
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(10)	(29)	(6)	(94)
Other comprehensive income (loss)	3	41	(1)	106
Balance at end of period	(7)	12	(7)	12
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(589)	(119)	(650)	(101)
Other comprehensive income (loss)	132	(23)	193	(41)
Balance at end of period	(457)	(142)	(457)	(142)
Total
Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(599)	(148)	(656)	(195)
Balance at end of period	$ (464)	$ (130)	$ (464)	$ (130)

Credit Facility (Details)

Credit Facility (Details) - USD ($)	Jul. 01, 2017	Jul. 29, 2013
Line of Credit Facility [Abstract]
Maximum borrowing capacity		$ 50,000,000
Outstanding revolving loans	$ 0

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Income Tax Disclosure [Abstract]
Provision for income taxes	$ 177	$ 124	$ 850	$ 245
Effective tax rate	(0.90%)	(2.20%)	(1.70%)	(1.50%)

Restructuring Charges (Details)

Restructuring Charges (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 01, 2017	Jun. 25, 2016	Jul. 01, 2017	Jun. 25, 2016
Restructuring Reserve [Roll Forward]
Restructuring charges for the period	$ 957	$ 0	$ 1,656	$ 0
Expected restructuring charges	6,800		6,800
Expected additional charges	5,100		5,100
Employee Severance
Restructuring Reserve [Roll Forward]
Liability at beginning of period	699		0
Restructuring charges for the period	957		1,656
Cash payments	(1,056)		(1,056)
Liability at end of period	$ 600		$ 600

Subsequent Event (Details)

Subsequent Event (Details) - USD ($)	Aug. 08, 2017	Aug. 01, 2017	Jul. 29, 2013
Subsequent Event [Line Items]
Maximum borrowing capacity			$ 50,000,000
Silicon Valley Bank | Subsequent Event
Subsequent Event [Line Items]
Early termination fees, amount	$ 300,000
Silicon Valley Bank | Letter of Credit | Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 10,000,000
Silicon Valley Bank | Non Formula Revolver | Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity		5,000,000
Silicon Valley Bank | Revolving Credit Facility | Subsequent Event
Subsequent Event [Line Items]
Maximum borrowing capacity		$ 30,000,000
Maximum amount outstanding during period	$ 30,000,000
Minimum | Prime Rate | Silicon Valley Bank | Subsequent Event
Subsequent Event [Line Items]
Basis spread on variable rate	0.50%
Minimum | LIBOR | Silicon Valley Bank | Subsequent Event
Subsequent Event [Line Items]
Basis spread on variable rate	2.00%
Maximum | Prime Rate | Silicon Valley Bank | Subsequent Event
Subsequent Event [Line Items]
Basis spread on variable rate	1.50%
Maximum | LIBOR | Silicon Valley Bank | Subsequent Event
Subsequent Event [Line Items]
Basis spread on variable rate	3.00%