Fitbit 10-Q 4 Aug 16 2016 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jul. 02, 2016	Jul. 31, 2016
Entity Information [Line Items]
Entity Registrant Name	FITBIT INC
Entity Central Index Key	1,447,599
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Jul. 2, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q2
Amendment Flag	false
Common Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		164,101,170
Common Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		58,052,784

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 416,142	$ 535,846
Marketable securities	343,534	128,632
Accounts receivable, net	377,545	469,260
Inventories	190,644	178,146
Prepaid expenses and other current assets	59,782	43,530
Total current assets	1,387,647	1,355,414
Property and equipment, net	74,181	44,501
Goodwill	25,217	22,157
Intangible assets, net	15,090	12,216
Deferred tax assets	119,472	83,020
Other assets	1,504	1,758
Total assets	1,623,111	1,519,066
Current liabilities:
Accounts payable	226,418	260,842
Accrued liabilities	231,921	194,977
Deferred revenue	46,420	44,448
Fitbit Force recall reserve	2,148	5,122
Income taxes payable	2,074	2,868
Total current liabilities	508,981	508,257
Other liabilities	47,473	29,358
Total liabilities	556,454	537,615
Commitments and contingencies
Stockholders’ equity:
Class A and Class B common stock	22	21
Additional paid-in capital	804,656	737,820
Accumulated other comprehensive income	1,684	691
Retained earnings	260,295	242,919
Total stockholders’ equity	1,066,657	981,451
Total liabilities and stockholders’ equity	$ 1,623,111	$ 1,519,066

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Income Statement [Abstract]
Revenue	$ 586,528	$ 400,412	$ 1,091,884	$ 737,166
Cost of revenue	341,559	212,870	613,160	380,415
Gross profit	244,969	187,542	478,724	356,751
Operating expenses:
Research and development	79,909	30,492	152,157	52,918
Sales and marketing	118,138	69,690	225,189	113,557
General and administrative	37,262	14,648	72,964	27,629
Change in contingent consideration	0	(7,704)	0	(7,704)
Total operating expenses	235,309	107,126	450,310	186,400
Operating income	9,660	80,416	28,414	170,351
Interest income (expense), net	839	(379)	1,421	(846)
Other income (expense), net	(463)	(45,308)	1,105	(58,385)
Income before income taxes	10,036	34,729	30,940	111,120
Income tax expense	3,695	17,048	13,564	45,442
Net income	6,341	17,681	17,376	65,678
Less: noncumulative dividends to preferred stockholders	0	(1,212)	0	(2,526)
Less: undistributed earnings to participating securities	0	(11,244)	0	(45,907)
Net income attributable to common stockholders—basic	6,341	5,225	17,376	17,245
Add: adjustments to undistributed earnings to participating securities	0	1,862	0	7,003
Net income attributable to common stockholders—diluted	$ 6,341	$ 7,087	$ 17,376	$ 24,248
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.03	$ 0.09	$ 0.08	$ 0.35
Diluted (in dollars per share)	$ 0.03	$ 0.07	$ 0.07	$ 0.29
Shares used to compute net income per share attributable to common stockholders:
Basic (in shares)	218,850	58,548	217,431	49,922
Diluted (in shares)	242,328	95,190	242,153	82,841

Condensed Consolidated Stateme4

Condensed Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Net income	$ 6,341	$ 17,681	$ 17,376	$ 65,678
Cash flow hedges:
Change in unrealized gain (loss) on cash flow hedges, net of tax benefit (expense) of $(245), $ —, $1,469, and $ — respectively	5,538	0	3,005	0
Less: reclassification for realized net gains included in net income, net of tax expense (benefit) of $(216), $ —, $509, and $ — respectively	(407)	0	(1,978)	0
Net change, net of tax	5,131	0	1,027	0
Change in foreign currency translation adjustment, net of tax	(88)	41	(160)	85
Change in unrealized loss on available-for-sale investments, net of tax	67	0	126	0
Comprehensive income	$ 11,451	$ 17,722	$ 18,369	$ 65,763

Condensed Consolidated Stateme5

Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Statement of Comprehensive Income [Abstract]
Change in unrealized gain (loss) on cash flow hedges, tax	$ (245)	$ 0	$ 1,469	$ 0
Reclassification for realized net gains included in net income, tax	$ (216)	$ 0	$ 509	$ 0

Condensed Consolidated Stateme6

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015
Cash Flows from Operating Activities
Net income	$ 17,376	$ 65,678
Adjustments to reconcile net income to net cash provided by operating activities:
Provision for inventory obsolescence	665	4,537
Depreciation	13,121	7,519
Write-off of property and equipment	649	0
Amortization of intangible assets	1,066	655
Revaluation of redeemable convertible preferred stock warrant liability	0	56,655
Stock-based compensation	38,170	12,650
Change in contingent consideration	0	(7,704)
Deferred income taxes	(36,452)	(20,111)
Excess of tax benefit from stock-based compensation	(16,275)	0
Other	(700)	294
Changes in operating assets and liabilities, net of acquisition:
Accounts receivable	91,537	(12,834)
Inventories	(13,351)	(76,334)
Prepaid expenses and other assets	(16,085)	(2,495)
Fitbit Force recall reserve	(2,974)	(9,581)
Accounts payable	(39,425)	(5,561)
Accrued liabilities and other liabilities	54,000	8,830
Deferred revenue	1,973	11,789
Income taxes payable	14,857	(29,836)
Net cash provided by operating activities	108,152	4,151
Cash Flows from Investing Activities
Purchase of property and equipment	(36,745)	(11,745)
Purchases of marketable securities	(392,738)	0
Sales of marketable securities	38,814	0
Maturities of marketable securities	140,262	0
Acquisitions, net of cash acquired	(5,600)	(11,037)
Net cash used in investing activities	(256,007)	(22,782)
Cash Flows from Financing Activities
Payments of offering costs	(1,236)	(2,522)
Proceeds from issuance of common stock	14,467	442
Taxes paid related to net share settlement of restricted stock units	(1,107)	0
Excess of tax benefit from stock-based compensation	16,275	0
Net proceeds from initial public offering	0	420,885
Proceeds from issuance of debt and revolving credit facility, net debt discount	0	160,000
Repayment of debt	0	(294,503)
Net cash provided by financing activities	28,399	284,302
Net increase (decrease) in cash and cash equivalents	(119,456)	265,671
Effect of exchange rate on cash and cash equivalents	(248)	(21)
Cash and cash equivalents at beginning of period	535,846	195,626
Cash and cash equivalents at end of period	416,142	461,276
Supplemental Disclosure
Cash paid for interest	287	103
Cash paid for income taxes	16,196	94,966
Supplemental Disclosure of Non-Cash Investing and Financing Activity
Purchase of property and equipment included in accounts payable and accrued liabilities	17,227	2,714
Conversion of redeemable convertible preferred stock into Class B common stock	0	67,814
Reclassification of redeemable convertible preferred stock warrant liability to additional paid-in capital	0	72,452
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants	0	56,678
Deferred offering costs included in accounts payable and accruals	0	2,711
Issuance of common stock in connection with acquisitions	$ 0	$ 13,317

Basis of Presentation and Summa

Basis of Presentation and Summary of Significant Accounting Policies	6 Months Ended
	Jul. 02, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	Basis of Presentation and Summary of Significant Accounting Policies The accompanying condensed consolidated financial statements are unaudited. The condensed consolidated balance sheet at December 31, 2015 has been derived from the audited financial statements of the Company. The accompanying condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America, or U.S. GAAP, for interim financial information, and in management’s opinion, includes all adjustments, consisting of only normal recurring adjustments, necessary for the fair statement of the Company’s financial position, its results of operations, and cash flows for the interim periods presented. The results of operations for the three and six months ended July 2, 2016 are not necessarily indicative of the results to be expected for the full fiscal year or any other period. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015, filed with the Securities and Exchange Commission on February 29, 2016. There have been no significant changes in the Company’s accounting policies from those disclosed in its Annual Report on Form 10-K. The Company’s fiscal year ends on December 31 of each year. In the first quarter of 2016, the Company adopted a 4-4-5 week quarterly calendar, which, for the 2016 fiscal year, is comprised of four fiscal quarters ending on April 2, 2016, July 2, 2016, October 1, 2016 and December 31, 2016. The Company did not adjust operating results for quarters prior to 2016. There were 91 days in each of the three months ended July 2, 2016 and June 30, 2015 , and 184 and 181 days in the six months ended July 2, 2016 and June 30, 2015 , respectively. The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated. Use of Estimates The preparation of condensed consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the condensed consolidated financial statements and accompanying notes. The primary estimates and assumptions made by management related to revenue recognition, reserves for sales returns and incentives, reserves for warranty, valuation of stock options, fair value of derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, accruals for the Fitbit Force recall, fair value of goodwill and acquired tangible and intangible assets and liabilities assumed during acquisitions, the number of reporting segments, the recoverability of intangible assets and their useful lives, contingencies, and the valuations of deferred income tax assets and uncertain tax positions. Actual results could differ from those estimates, and such differences may be material to the condensed consolidated financial statements. Out-of-Period Adjustment During the first quarter of 2016, the Company identified an error, which resulted in an understatement of income tax expense by $3.0 million for the year ended December 31, 2015. The Company recorded an out-of-period adjustment to correct the error in the quarter ended April 2, 2016. The Company assessed the materiality of this error and concluded the error was not material to 2015 consolidated financial statements and is not expected to be material to 2016 consolidated financial statements, and therefore, the Company recorded the correction in the first quarter of 2016. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09 (ASC 606), Revenue from Contracts with Customers , which affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. 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 currently effective 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. In July 2015, the FASB approved a one-year deferral of the effective date of the standard. ASU 2014-09 will become effective for the Company on January 1, 2018 and can be adopted either retrospectively to each prior reporting period presented or as a cumulative effect adjustment as of the date of adoption. Early adoption is permitted but not before the original effective date of annual periods beginning after December 15, 2016. In April 2016, the FASB issued ASU 2016-10, which clarifies guidance on identifying performance obligations and licensing implementation. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases . This ASU requires lease assets and lease liabilities arising from leases, including operating leases, to be recognized on the balance sheet. ASU 2016-02 will become effective for the Company on January 1, 2019, and requires adoption using a modified retrospective approach. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (Topic 718). This ASU simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 will become effective for the Company on January 1, 2017 and early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU provides for a new impairment model which requires measurement and recognition of expected credit losses for most financial assets and certain other instruments. ASU 2016-13 will become effective for the Company on January 1, 2020 and early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jul. 02, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The carrying values of the Company’s accounts receivable, accounts payable, and accrued liabilities approximated their fair values due to the short period of time to maturity or repayment. The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): July 2, 2016 Level 1 Level 2 Total Assets: Money market funds $ 162,633 $ — $ 162,633 U.S. government agencies — 68,834 68,834 Corporate debt securities — 384,429 384,429 Derivative assets — 9,134 9,134 Total $ 162,633 $ 462,397 $ 625,030 Liabilities: Derivative liabilities $ — $ 5,964 $ 5,964 December 31, 2015 Level 1 Level 2 Total Assets: Money market funds $ 248,128 $ — $ 248,128 U.S. government agencies — 113,314 113,314 Corporate debt securities — 193,964 193,964 Derivative assets — 6,002 6,002 Total $ 248,128 $ 313,280 $ 561,408 Liabilities: Derivative liabilities $ — $ 2,640 $ 2,640 The fair value of the Company’s Level 1 financial instruments is based on quoted market prices in active markets for identical instruments. The fair value of the Company’s Level 2 financial instruments is based on observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data. In addition, Level 2 assets and liabilities include derivative financial instruments associated with hedging activity, which are further discussed in Note 3. Derivative financial instruments are initially measured at fair value on the contract date and are subsequently remeasured to fair value at each reporting date using inputs such as spot rates, forward rates, and discount rates. There is not an active market for each hedge contract, but the inputs used to calculate the value of the instruments are tied to active markets. There were no Level 3 assets or liabilities as of July 2, 2016 and December 31, 2015. There have been no transfers between fair value measurement levels during the three and six months ended July 2, 2016 and June 30, 2015 .

Financial Instruments

Financial Instruments	6 Months Ended
	Jul. 02, 2016
Investments, Debt and Equity Securities [Abstract]
Financial Instruments	Financial Instruments Cash, Cash Equivalents, and Marketable Securities The Company’s marketable securities are classified as available-for-sale as of the balance sheet date and are reported at fair value with unrealized gains and losses reported, net of tax, as a separate component of accumulated other comprehensive income (loss) in stockholders’ equity. Because the Company views marketable securities as available to support current operations as needed, it has classified all available-for-sale securities as current assets. Realized gains or losses and other-than-temporary impairments, if any, on available-for-sale securities are reported in other income (expense), net as incurred. Investments are reviewed periodically to identify potential other-than-temporary impairments. No impairment loss has been recorded on the securities included in the tables below as the Company believes that the decrease in fair value of these securities is temporary and expects to recover up to, or beyond, the initial cost of investment for these securities. The following table sets forth cash, cash equivalents, and marketable securities as of July 2, 2016 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 143,780 $ — $ — $ 143,780 $ 143,780 $ — Money market funds 162,633 — — 162,633 162,633 — U.S. government agencies 68,767 67 — 68,834 — 68,834 Corporate debt securities 384,425 36 (32 ) 384,429 109,729 274,700 Total $ 759,605 $ 103 $ (32 ) $ 759,676 $ 416,142 $ 343,534 The following table sets forth cash, cash equivalents, and marketable securities as of December 31, 2015 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 109,072 $ — $ — $ 109,072 $ 109,072 $ — Money market funds 248,128 — — 248,128 248,128 — U.S. government agencies 113,315 3 (4 ) 113,314 63,464 49,850 Corporate debt securities 194,018 1 (55 ) 193,964 115,182 78,782 Total $ 664,533 $ 4 $ (59 ) $ 664,478 $ 535,846 $ 128,632 The gross unrealized gains or losses on marketable securities as of July 2, 2016 and December 31, 2015 were not material. There were no available-for-sale investments as of July 2, 2016 and December 31, 2015 that have been in a continuous unrealized loss position for greater than twelve months. The following table classifies marketable securities by contractual maturities (in thousands): July 2, 2016 December 31, 2015 Due in one year $ 341,041 $ 128,632 Due in one to two years 2,493 — Total $ 343,534 $ 128,632 Derivative Financial Instruments The Company operates in foreign countries, which exposes it to market risk associated with foreign currency exchange rate fluctuations between the U.S. dollar and various foreign currencies. In order to manage this risk, the Company may hedge a portion of its foreign currency exposures related to outstanding monetary assets and liabilities as well as forecasted revenues and expenses, using foreign currency exchange forward or option contracts. In general, the market risk related to these contracts is offset by corresponding gains and losses on the hedged transactions. The Company does not enter into derivative contracts for trading or speculative purposes. Cash Flow Hedges Beginning in the third quarter of 2015, the Company has entered into foreign currency derivative contracts designated as cash flow hedges to hedge certain forecasted revenue and expense transactions denominated in currencies other than the U.S. dollar. The Company’s cash flow hedges consist of forward contracts with maturities of 12 months or less. The Company periodically assesses the effectiveness of its cash flow hedges. Effectiveness represents a derivative instrument’s ability to generate offsetting changes in cash flows related to the hedged risk. All elements of the hedged transaction are included in the effectiveness assessment. The Company records the gains or losses, net of tax, related to the effective portion of its cash flow hedges as a component of accumulated other comprehensive income (loss) in stockholders’ equity and subsequently reclassifies the gains or losses into revenue and operating expenses when the underlying hedged transactions are recognized. The Company records the gains or losses related to the ineffective portion of the cash flow hedges, if any, immediately in other income (expense), net. If the hedged transaction becomes probable of not occurring, the corresponding amounts in accumulated other comprehensive income (loss) would immediately be reclassified to other income (expense), net. Cash flows related to the Company’s cash flow hedging program are recognized as cash flows from operating activities in its statements of cash flows. The Company had outstanding contracts with a total notional amount of $246.9 million and $50.8 million in cash flow hedges for forecasted revenue and expense transactions, respectively, as of July 2, 2016 , and $254.1 million in cash flow hedges for forecasted revenue transactions as of December 31, 2015 . Balance Sheet Hedges The Company enters into foreign exchange contracts to hedge certain monetary assets and liabilities that are denominated in currencies other than the functional currency of its subsidiaries. These foreign exchange contracts are carried at fair value, do not qualify for hedge accounting treatment, and are not designated as hedging instruments. Changes in the value of the foreign exchange contracts are recognized in other income (expense), net and offset the foreign currency gain or loss on the underlying net monetary assets or liabilities. The Company had outstanding balance sheet hedges with a total notional amount of $104.3 million and $104.8 million as of July 2, 2016 and December 31, 2015 , respectively. Fair Value of Foreign Currency Derivatives The foreign currency derivative contracts that were not settled at the end of the period are recorded at fair value, on a gross basis, in the condensed consolidated balance sheets. The following table presents the fair value of the Company’s foreign currency derivative contracts as of the periods presented (in thousands): July 2, 2016 December 31, 2015 Balance Sheet Location Fair Value Derivative Assets Fair Value Derivative Liabilities Fair Value Derivative Assets Fair Value Derivative Liabilities Cash flow designated hedges Prepaid expenses and other current assets $ 5,211 $ — $ 3,116 $ — Cash flow designated hedges Accrued liabilities — 3,101 — 1,327 Hedges not designated Prepaid expenses and other current assets 3,923 — 2,886 — Hedges not designated Accrued liabilities — 2,863 — 1,313 Total fair value of derivative instruments $ 9,134 $ 5,964 $ 6,002 $ 2,640 Financial Statement Effect of Foreign Currency Derivative Contracts The following table presents the pre-tax impact of the Company’s foreign currency derivative contracts on other comprehensive income, or OCI, and the condensed consolidated statements of operations for the periods presented (in thousands): Three Months Ended Six Months Ended Income Statement Location July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Foreign exchange cash flow hedges Gain (loss) recognized in OCI – effective portion $ 5,783 $ — $ 1,535 $ — Gain (loss) reclassified from OCI into income – effective portion Revenue (1,380 ) — (1,550 ) — Gain (loss) reclassified from OCI into income – effective portion Operating expenses 1,393 — 2,408 — Gain (loss) recognized in income – ineffective portion Other income (expense), net (95 ) — (185 ) — Foreign exchange balance sheet hedges Gain (loss) recognized in income Other income (expense), net $ (72 ) $ 434 $ (209 ) $ 2,454 As of July 2, 2016 , all net derivative gains related to the Company’s cash flow hedges will be reclassified from OCI into net income within the next 12 months. Offsetting of Foreign Currency Derivative Contracts The Company presents its derivative assets and derivative liabilities at gross fair values in the condensed consolidated balance sheets. The Company generally enters into master netting arrangements, which mitigate credit risk by permitting net settlement of transactions with the same counterparty. The Company is not required to pledge, and is not entitled to receive, cash collateral related to these derivative instruments. The following tables set forth the available offsetting of net derivative assets under the master netting arrangements as of July 2, 2016 and December 31, 2015 (in thousands): As of July 2, 2016 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Received Net Amount Foreign exchange contracts $ 9,134 $ — $ 9,134 $ 4,960 $ — $ 4,174 As of December 31, 2015 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Received Net Amount Foreign exchange contracts $ 6,002 $ — $ 6,002 $ 2,100 $ — $ 3,902 The following tables set forth the available offsetting of net derivative liabilities under the master netting arrangements as of July 2, 2016 and December 31, 2015 (in thousands): As of July 2, 2016 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Pledged Net Amount Foreign exchange contracts $ 5,964 $ — $ 5,964 $ 4,960 $ — $ 1,004 As of December 31, 2015 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Pledged Net Amount Foreign exchange contracts $ 2,640 $ — $ 2,640 $ 2,100 $ — $ 540

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jul. 02, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Revenue Reserve Revenue returns reserve activities were as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 55,875 $ 26,362 $ 74,045 $ 26,559 Increases 85,335 32,859 119,550 53,352 Returns taken (60,933 ) (23,956 ) (113,318 ) (44,646 ) Ending balances $ 80,277 $ 35,265 $ 80,277 $ 35,265 Inventories Inventories consisted of the following (in thousands): July 2, 2016 December 31, 2015 Components $ 1,699 $ 5,359 Finished goods 188,945 172,787 Total inventories $ 190,644 $ 178,146 Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): July 2, 2016 December 31, 2015 POP displays, net $ 23,801 $ 9,990 Derivative assets 9,134 6,002 Prepaid income taxes 638 11,889 Prepaid expenses and other current assets 26,209 15,649 Total prepaid expenses and other current assets $ 59,782 $ 43,530 Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): July 2, 2016 December 31, 2015 Tooling and manufacturing equipment $ 74,198 $ 53,092 Furniture and office equipment 8,483 6,809 Purchased and internally-developed software 6,770 3,794 Leasehold improvements 22,010 8,388 Total property and equipment 111,461 72,083 Less: Accumulated depreciation and amortization (37,280 ) (27,582 ) Property and equipment, net $ 74,181 $ 44,501 Goodwill and Intangible Assets The carrying amount of goodwill was $ 25.2 million and $22.2 million as of July 2, 2016 and December 31, 2015 , respectively, and the increase in the carrying amount during the three and six months ended July 2, 2016 was attributable to an acquisition in May 2016. See Note 11 for additional information. The carrying amounts of the intangible assets as of July 2, 2016 and December 31, 2015 were as follows (in thousands, except useful life). In-process research and development is not amortized until the completion of the related development. July 2, 2016 December 31, 2015 Weighted Average Remaining Useful Life (years) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Developed technology $ 12,640 $ (2,345 ) $ 10,295 $ 12,640 $ (1,442 ) $ 11,198 5.8 Trademarks and other 1,278 (423 ) 855 1,278 (260 ) 1,018 3.7 Total finite-lived intangible assets subject to amortization, net 13,918 (2,768 ) 11,150 13,918 (1,702 ) 12,216 In-process research and development 3,940 — 3,940 — — — Total intangible assets, net $ 17,858 $ (2,768 ) $ 15,090 $ 13,918 $ (1,702 ) $ 12,216 Total amortization expense related to intangible assets was $0.5 million for each of the three months ended July 2, 2016 and June 30, 2015 , and $1.1 million and $0.7 million for the six months ended July 2, 2016 and June 30, 2015 , respectively. The estimated future amortization expense of acquired finite-lived intangible assets to be charged to cost of revenue and operating expenses after July 2, 2016 , is as follows (in thousands): Cost of Revenue Operating Expenses Total Remaining 2016 $ 903 $ 118 $ 1,021 2017 1,806 230 2,036 2018 1,806 230 2,036 2019 1,806 230 2,036 2020 1,806 47 1,853 Thereafter 2,168 — 2,168 Total finite-lived intangible assets, net $ 10,295 $ 855 $ 11,150 Accrued Liabilities Accrued liabilities consisted of the following (in thousands): July 2, 2016 December 31, 2015 Product warranty $ 76,841 $ 40,212 Accrued sales and marketing 45,736 33,389 Employee related liabilities 23,421 27,394 Accrued co-op advertising and marketing development funds 18,879 29,077 Accrued sales incentives 17,670 24,324 Accrued manufacturing expense and freight 12,982 10,723 Inventory received but not billed 6,759 4,292 Derivative liabilities 5,964 2,640 Sales taxes and VAT payable 5,753 8,349 Accrued legal fees 3,326 3,138 Customer deposits 1,006 2,062 Other 13,584 9,377 Accrued liabilities $ 231,921 $ 194,977 Product warranty reserve activities were as follows (in thousands) (1) : Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 50,669 $ 23,251 $ 40,212 $ 20,098 Charged to cost of revenue 50,480 14,568 78,024 22,065 Settlement of claims (24,308 ) (6,756 ) (41,395 ) (11,100 ) Ending balances $ 76,841 $ 31,063 $ 76,841 $ 31,063 (1) Does not include reserves established as a result of the recall of the Fitbit Force. See the section titled “—Fitbit Force Recall Reserve” for additional information regarding such reserves. Fitbit Force Recall Reserve In March 2014, the Company announced a recall for one of its products, the Fitbit Force, or Fitbit Force Recall. The product recall, which is regulated by the U.S. Consumer Product Safety Commission, covered all Fitbit Force units sold since the product was first introduced in October 2013. The product recall program has no expiration date. As a result of the product recall, the Company established reserves that include cost estimates for customer refunds, logistics and handling fees for managing product returns and processing refunds, obsolescence of on-hand inventory, cancellation charges for existing purchase commitments and rework of component inventory with the contract manufacturer, write-offs of tooling and manufacturing equipment, and legal settlement costs. Fitbit Force Recall reserve activities were as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 4,339 $ 15,104 $ 5,122 $ 22,476 Charged (benefit) to cost of revenue — — — (2,040 ) Charged (benefit) to general and administrative — 69 — (73 ) Settlement of claims (2,191 ) (2,279 ) (2,974 ) (7,469 ) Ending balances $ 2,148 $ 12,894 $ 2,148 $ 12,894 Accumulated Other Comprehensive Income The components and activity of accumulated other comprehensive income, or AOCI, net of tax, were as follows (in thousands): Unrealized Gains (Losses) on Cash Flow Hedges Currency Translation Adjustments Unrealized Gains (Losses) on Available-for-Sale Investments Total Balance at December 31, 2015 $ 751 $ (5 ) $ (55 ) $ 691 Other comprehensive income (loss) before reclassifications 3,005 (160 ) 126 2,971 Amounts reclassified from AOCI (1,978 ) — — (1,978 ) Other comprehensive income (loss) 1,027 (160 ) 126 993 Balance at July 2, 2016 $ 1,778 $ (165 ) $ 71 $ 1,684 Other comprehensive income consisted only of currency translation adjustments of an immaterial amount in the six months ended June 30, 2015 .

Long-Term Debt

Long-Term Debt	6 Months Ended
	Jul. 02, 2016
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt 2014 Credit Agreement In August 2014, the Company entered into an amended and restated credit agreement, or Asset-Based Credit Facility, with a borrowing limit of $180.0 million . The Asset-Based Credit Facility allowed the Company to borrow up to the lesser of (i) $180.0 million , including up to $50.0 million for the issuance of letters of credit and up to $25.0 million for swing line loans and (ii) the borrowing base then in effect less the amount then outstanding under letters of credit and loans. During the six months ended June 30, 2015 , the effective interest rate on the revolving line of credit was 4.25% . The Asset-Based Credit Facility was terminated in December 2015. 2014 Revolving Credit and Guarantee Agreement In August 2014, the Company entered into a revolving credit and guarantee agreement, or Cash Flow Facility. In October 2014, the Company amended the Cash Flow Facility to increase the borrowing limit under the Cash Flow Facility. The Cash Flow Facility allowed the Company to borrow up to $50.0 million , including up to $10.0 million for the issuance of letters of credit and up to $10.0 million for swing line loans. During the six months ended June 30, 2015 , the effective interest rate on the revolving line of credit was 3.59% . The Cash Flow Facility was terminated in December 2015. 2015 Credit Agreement In December 2015, the Company entered into a second amended and restated credit agreement, or Senior Facility, to replace the existing Asset-Based Credit Facility and Cash Flow Facility. This Senior Facility allows the Company to borrow up to $250.0 million , including up to a $50.0 million for the issuance of letters of credit and up to $25.0 million for swing line loans. Borrowings under the Senior Facility may be drawn as Alternate Base Rate, or ABR, loans or Eurodollar loans, and matures in December 2020. ABR loans bear interest at a variable rate equal to the applicable margin plus the highest of (i) the prime rate, (ii) the federal funds effective rate plus 0.5% , and (iii) the Eurodollar rate plus 1.0% , but in any case at a minimum rate of 3.25% per annum. Eurodollar loans bear interest at a variable rate based on the LIBOR rate and Eurodollar reserve requirements, but in any case at a minimum rate of 1.0% per annum. The Company has the option to repay its borrowings under the Senior Facility without penalty prior to maturity. The Senior Facility requires the Company to comply with certain financial covenants, including maintaining a consolidated fixed charge coverage ratio of at least 1.15 :1, and a consolidated leverage ratio of less than 3 :1. The Senior Facility also requires the Company to comply with certain non-financial covenants. The Senior Facility contains customary covenants that restrict the Company’s ability to, among other things, incur additional indebtedness, sell certain assets, guarantee certain obligations of third parties, declare dividends or make certain distributions, and undergo a merger or consolidation or other transactions. The Company was in compliance with these covenants as of July 2, 2016 . Obligations under the credit facility are collaterized by substantially all of the Company’s assets, excluding the Company’s intellectual property. As of July 2, 2016 , there were no outstanding borrowings under the Senior Facility. Letters of Credit As of July 2, 2016 and December 31, 2015 , the Company had outstanding letters of credit totaling $37.9 million and $17.1 million , respectively, issued to cover various security deposits on the Company’s facility leases.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jul. 02, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company leases office space in various locations with expiration dates between 2016 and 2024. The lease agreements often include leasehold improvement incentives, escalating lease payments, renewal provisions and other provisions which require the Company to pay taxes, insurance, maintenance costs or defined rent increases. Rent expense is recorded over the lease terms on a straight-line basis. In April 2016, the Company entered into a sublease to expand the Company’s existing headquarters. The lease expires in 2024. Future minimum payments under the leases as of July 2, 2016 were $309.9 million . Legal Proceedings Fitbit Force. In 2014, class action and personal injury lawsuits were filed against the Company based upon claims of allergic reactions from adhesives in the Fitbit Force, and alleged violations of various state false advertising and unfair competition statutes based on the Company’s sale and marketing of the Fitbit Force. The class action cases were settled in 2014. Certain personal injury complaints were filed in 2015, and the settlement of those claims is almost final. In the fourth quarter of 2015, the Company received proceeds from the insurance policies that apply to these claims and related legal fees, and the Company recorded an accrual for liabilities arising under these claims that was immaterial and falls within the amount of the insurance proceeds received. Fitbit Zip, Fitbit One, Fitbit Flex, Fitbit Charge, Fitbit Charge HR, and Fitbit Surge. In 2014, one personal injury lawsuit was filed against the Company based upon claims of skin irritation from the Fitbit Flex. Additional lawsuits were filed in 2015 based upon claims of personal injury from the Fitbit Zip, Fitbit One, Fitbit Flex, Fitbit Charge, Fitbit Charge HR, and Fitbit Surge. Settlement of those claims is almost final. In the fourth quarter of 2015, the Company received proceeds from the insurance policies that apply to these claims and related legal fees, and the Company recorded an accrual for liabilities arising under these claims that was immaterial and falls within the amount of the insurance proceeds received. Jawbone. On May 27, 2015, Aliphcom, Inc. d/b/a Jawbone, or Jawbone, filed a lawsuit against the Company and certain of its employees who were formerly employed by Jawbone in the Superior Court of the State of California in the County of San Francisco alleging trade secret misappropriation and unfair and unlawful business practices against all defendants, and alleging breach of contract and breach of implied covenant of good faith and fair dealing against the employee defendants. The complaint alleges, among other things, that prior to leaving Jawbone at various times in 2015, the employees downloaded Jawbone company documents and materials, including allegedly confidential and trade secret information, and that these employees are using such information in the development of the Company’s products. The complaint also alleges that the Company recruited those employees with the intent of using Jawbone’s proprietary information. The complaint seeks unspecified damages, including punitive damages and injunctive relief. On June 26, 2015, the Company and the employee defendants filed demurrers to Jawbone’s complaint. The Company sought to dismiss both causes of action brought against it (those for misappropriation of trade secrets and unfair business practices). The employee defendants sought to dismiss the breach of implied covenant and unfair business practices causes of action. On October 2, 2015, Jawbone filed a First Amended Complaint asserting the same causes of action and adding additional allegations to those raised in the initial complaint. On October 21, 2015, the Company and the employee defendants demurred to the First Amended Complaint, in which the Company once again moved to dismiss the misappropriation and unfair business practices causes of action and the employee defendants moved to dismiss those for breach of the implied covenant and unfair business practices. A hearing on the demurrers was held on May 31, 2016, and the Court granted the demurrer on the unfair business practices cause of action as to both Fitbit and the individual defendants. On May 31, 2016, Jawbone again moved to amend its complaint to add another employee defendant to the lawsuit. The Second Amended Complaint, adding the employee defendant and additional allegations, was filed on June 23, 2016. On June 10, 2015, Jawbone and BodyMedia, Inc., a wholly-owned subsidiary of Jawbone, or BodyMedia, filed a lawsuit against the Company in the U.S. District Court for the Northern District of California alleging that the Company infringes three U.S. patents held by them: U.S. Patent No. 8,446,275, titled “General Health and Wellness Management Method and Apparatus For A Wellness Application Using Data From a Data-Capable Band,” U.S. Patent No. 8,073,707, titled “System For Detecting, Monitoring, And Reporting An Individual’s Physiological Or Contextual Status,” and U.S. Patent No. 8,398,546, titled “System For Monitoring And Managing Body Weight And Other Physiological Conditions Including Iterative And Personalized Planning, Intervention And Reporting Capability.” Jawbone and BodyMedia allege that these patents have been infringed by a substantial majority of the Company’s products that it has sold historically, as well as several current products. The complaint seeks unspecified compensatory damages and attorney’s fees from the Company and to permanently enjoin the Company from making, manufacturing, using, selling, importing, or offering the Company’s products for sale. On July 3, 2015, Jawbone and BodyMedia amended their complaint to add three additional U.S. patents to the infringement claims against the Company: U.S. Patent No. 8,529,811, titled “Component Protective Overmolding Using Protective External Coatings,” U.S. Patent No. 8,793,522, titled “Power Management in a Data-Capable Strapband,” and U.S. Patent No. 8,961,413, titled “Wireless Communications Device and Personal Monitor.” On July 7, 2015, Jawbone and BodyMedia filed a complaint with the ITC requesting an investigation into purported violations of the Tariff Act of 1930 by the Company and Flextronics International Ltd. and Flextronics Sales and Marketing (A-P) Ltd. The complaint alleges that the Company’s products infringe the same six U.S. patents at issue in action brought against the Company in the U.S. District Court for the Northern District of California. Furthermore, the complaint makes the same allegations of trade secret misappropriation, unfair competition and unfair acts as a result of the Company’s hiring of the former Jawbone employees, as in the action brought against it and certain of the Company’s employees in the Superior Court in the State of California. The complaint seeks a limited exclusion order and a cease and desist order halting the importation and sale of the Company’s products that allegedly infringe upon Jawbone’s patents and misappropriate Jawbone’s trade secrets. On July 24, 2015, Jawbone and BodyMedia filed a letter with the ITC seeking to amend and supplement their ITC complaint. In their letter, Jawbone and BodyMedia, among other things, purport to identify the trade secrets allegedly misappropriated by the employee defendants. The ITC instituted the investigation on August 17, 2015. On February 8, 2016, Jawbone filed a motion for partial termination of the investigation as to the ‘522 patent after discovery showed the Company’s products do not actually practice the patent. On March 4, 2016, Jawbone filed a motion for partial termination of the investigation as to the ‘811 patent after a claim construction ruling that was favorable to the Company suggested non-infringement by the Company’s products. On March 4, 2016, the administrative law judge, or ALJ, issued an Initial Determination that granted a Motion for Summary Determination as to the ‘546 and ‘275 patents on grounds they are ineligible subject matter under 35 U.S.C. § 101. The Initial Determination was affirmed by the ITC on April 4, 2016. On June 3, 2016, Jawbone filed a notice of appeal in the Federal Circuit. On April 28, 2016, the ALJ issued an Initial Determination that granted a Motion for Summary Determination as to the ‘707 and ‘413 patents on grounds they are ineligible subject matter under 35 U.S.C. § 101. The Initial Determination was affirmed by the ITC on June 2, 2016. A trial on the trade secrets allegations took place from May 9-17, 2016. The Initial Determination by the ALJ is due August 19, 2016, and the target date for completion of the investigation is December 21, 2016. On September 3, 2015, the Company filed a complaint for patent infringement against Jawbone in the U.S. District Court for the District of Delaware, asserting that its activity trackers (UP Move, UP24, UP3, and UP4) infringe U.S. Patent Nos. 8,909,543, 9,031,812, and 9,042,971. On September 8, 2015, the Company filed a complaint for patent infringement against Jawbone in the U.S. District Court for the Northern District of California, asserting that its activity trackers infringe U.S. Patent Nos. 9,026,053, 9,084,923, and 9,106,307. On October 29, 2015, the Company filed a complaint for patent infringement against Jawbone in the United States District Court for the District of Delaware, asserting that its activity trackers infringe U.S. Patent Nos. 8,920,332, 8,868,377, and 9,089,760. On November 2, 2015, the Company filed a complaint with the ITC requesting an investigation into violations of the Tariff Act of 1930 by Jawbone and Body Media. The complaint asserts that Jawbone’s products infringe U.S. Patent Nos. 8,920,332, 8,868,377, and 9,089,760. The complaint seeks a limited exclusion order and a cease and desist order halting the importation and sale of Jawbone’s products that the Company believes infringe upon its patents. The ITC instituted the investigation on December 1, 2015. On July 20, 2016, the administrative law judge, or ALJ, issued an Initial Determination that granted a Motion for Summary Determination as to the ‘332, ‘377, and ‘760 patents on grounds they are ineligible subject matter under 35 U.S.C. § 101. As a result, the investigation was terminated and the August 4, 2016 trial date cancelled. The case filed by Jawbone against the Company in the Northern District of California has been stayed, pending a determination in the ITC on the same patents. The first case filed by the Company against Jawbone in the District of Delaware, asserting the ’543, ’812, and ’971 patents, has been transferred to the Northern District of California. The second case filed by the Company against Jawbone in the District of Delaware, asserting the ’332, ’377, and ’760 patents, has been stayed, pending a determination in the ITC on the same patents. In the case filed by the Company in the Northern District of California, on October 30, 2015, Jawbone answered and made an antitrust counterclaim, asserting that the Company’s infringement claims are somehow “sham litigation” and that by asserting them and hiring some of Jawbone’s employees, the Company is supposedly monopolizing a market of personal fitness trackers. In response to the Company’s motion to dismiss the antitrust counterclaim, on January 13, 2016, Jawbone amended its Answer and antitrust counterclaim. The Company moved to stay and bifurcate the antitrust claim, and on May 27, 2016, the Court granted the motion. On June 15, 2016, Jawbone filed a Motion for Summary Judgment, which the Company opposed. On July 12, 2016, Jawbone withdrew its motion. The Company intends to vigorously defend and prosecute each of the Jawbone litigation matters and, based on its review, the Company believes it has valid defenses and claims with respect to each of these matters. However, litigation is inherently uncertain, and any judgment or injunctive relief entered against the Company or any adverse settlement could materially and adversely impact its business, financial condition, operating results, and prospects. Regarding the six matters still in the early stages of litigation, the Company is unable to estimate a reasonably possible loss or range of loss, if any, that may result from these matters. In addition, these litigation matters are complex, likely to involve significant management time and attention, and the cost of defending and prosecuting these matters is likely to be expensive, regardless of outcome. Sleep Tracking. On May 8, 2015, a purported class action lawsuit was filed against the Company in the U.S. District Court for the Northern District of California, alleging that the sleep tracking function available in certain trackers does not perform as advertised. Plaintiffs seek class certification, restitution, an award of unspecified compensatory and punitive damages, an award of reasonable costs and expenses, including attorneys’ fees, and other further relief as the Court may deem just and proper. Plaintiffs have amended their complaint four times, and on January 15, 2016, the Company moved to dismiss the Fourth Amended Complaint. On July 15, 2016, the Court denied the motion to dismiss. The Company believes that the plaintiffs’ allegations are without merit, and intends to vigorously defend against the claims. Because the Company is in the early stages of this litigation matter, the Company is unable to estimate a reasonably possible loss or range of loss, if any, that may result from this matter. Heart Rate Tracking . On January 6, 2016 and February 16, 2016, two purported class action lawsuits were filed against the Company in the U.S. District for the Northern District of California, alleging that the PurePulse heart rate tracking technology in the Fitbit Charge HR and Fitbit Surge do not consistently and accurately record users’ heart rates. Plaintiffs allege common law claims as well as violations of various states’ false advertising and unfair competition statutes based on our sale and marketing of the Fitbit Charge HR and Fitbit Surge. Plaintiffs seek class certification, injunctive and declaratory relief, restitution, an award of unspecified compensatory damages, exemplary damages, punitive damages, and statutory penalties and damages, an award of reasonable costs and expenses, including attorneys’ fees, and other further relief as the Court may deem just and proper. On April 15, 2016, the plaintiffs filed a Consolidated Master Class Action Complaint that combines the plaintiffs from the two previously filed complaints. On May 19, 2016, the plaintiffs filed an Amended Consolidated Master Class Action Complaint. Attached as an exhibit was a “study” commissioned by the plaintiffs and performed by two researchers at California State Polytechnic University, Pomona, which allegedly found that the Fitbit devices incorrectly measured heart rate by an average of 20 beats per minute during moderate to high exercise. The Company has not yet answered. On August 3, 2016, the parties appeared at a Case Management Conference to discuss whether the issue of arbitrability should be decided by the arbitrator. The Company believes that the plaintiffs’ allegations are without merit, and intends to vigorously defend against the claims. Because the Company is in the early stages of this litigation matter, the Company is unable to estimate a reasonably possible loss or range of loss, if any, that may result from this matter. Federal Securities Class Action . On January 11, 2016 a putative securities class action was filed in the U.S. District Court for the Northern District of California naming as defendants the Company and certain of its officers (the “Federal Securities Class Action”). On May 10, 2016, the Court appointed the Fitbit Investor Group (consisting of five individual investors) as lead plaintiff. The amended complaint, filed on July 1, 2016, names as defendants the Company, certain of its officers and directors, and certain financial institutions that acted as underwriters in connection with the Company’s June 2015 initial public offering, or IPO. Plaintiffs allege violations of the Securities Act of 1933, as amended, or the Securities Act, and the Securities Exchange Act of 1934, as amended, or the Exchange Act, based on alleged materially false and misleading statements about Fitbit’s products between October 27, 2014 and November 23, 2015. Plaintiffs seek to represent a class of persons who purchased or otherwise acquired the Company’s securities (i) on the open market between June 18, 2015 and May 19, 2016; and/or (ii) pursuant to or traceable to the IPO. Plaintiffs seek class certification, an award of unspecified compensatory damages, an award of reasonable costs and expenses, including attorneys’ fees, and other further relief as the Court may deem just and proper. The Company filed a motion to dismiss the Amended Complaint on July 29, 2016. The hearing date has not yet been scheduled. The Company believes that the plaintiffs’ allegations are without merit, and intends to vigorously defend against the claims. Because the Company is in the early stages of this litigation matter, the Company is unable to estimate a reasonably possible loss or range of loss, if any, that may result from this matter. State Securities Class Action . On April 28, 2016, a putative class action lawsuit alleging violations of the Securities Act was filed in the Superior Court of California, County of San Mateo, naming as defendants the Company, certain of its officers, its board members, the underwriters for the IPO, and a number of its investors (the “San Mateo Action”). On May 23, 2016, the Court granted plaintiff’s request to voluntarily dismiss the investor defendants. Plaintiff alleges that the IPO registration statement contained material misstatements about the Company’s products. Plaintiff seeks to represent a class of persons who purchased Fitbit common stock in and/or traceable to the IPO. Plaintiff seeks class certification, an award of unspecified compensatory damages, an award of reasonable costs and expenses, including attorneys’ fees, and other further relief as the Court may deem just and proper. On May 17, 2016, a shareholder class action lawsuit was filed in the Superior Court of California, County of San Francisco alleging claims similar to those at issue in the San Mateo Action and the Federal Securities Class Action (the “San Francisco Action”). The complaint alleges violations of the Securities Act based on alleged material misstatements in the registration statements for the IPO and November 2015 follow-on public offering and names as defendants Fitbit, certain of its officers and directors, the underwriters for Fitbit’s public offerings, and two of Fitbit’s investors. Plaintiff seeks to represent a class of persons who acquired Fitbit common stock pursuant and/or traceable to the IPO and follow-on public offering. The Company removed both the San Mateo Action and the San Francisco Action to the U.S. District Court for the Northern District of California. On July 27, 2016, the District Court remanded the actions back to state court. Defendants have not yet answered. The Company believes that the plaintiffs’ allegations in these actions are without merit, and intends to vigorously defend against the claims. Because the Company is in the early stages of this litigation matter, the Company is unable to estimate a reasonably possible loss or range of loss, if any, that may result from this matter. Other. The Company is and, from time to time, may in the future become, involved in other legal proceedings in the ordinary course of business. The Company currently believes that the outcome of any of these existing legal proceedings, including the aforementioned cases, either individually or in the aggregate, will not have a material impact on the operating results, financial condition or cash flows of the Company. With respect to existing legal proceedings, the Company has either determined that the existence of a material loss is not reasonably possible or that it is unable to estimate a reasonably possible loss or range of loss. The Company may incur substantial legal fees, which are expensed as incurred, in defending against these legal proceedings. Indemnifications In the ordinary course of business, the Company enters into agreements that may include indemnification provisions. Pursuant to such agreements, the Company may indemnify, hold harmless and defend an indemnified party for losses suffered or incurred by the indemnified party. Some of the provisions will limit losses to those arising from third-party actions. In some cases, the indemnification will continue after the termination of the agreement. The maximum potential amount of future payments the Company could be required to make under these provisions is not determinable. To date, the Company has not incurred material costs to defend lawsuits or settle claims related to these indemnification provisions. The Company has also entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers to the fullest extent permitted by Delaware corporate law. The Company also currently has directors’ and officers’ insurance.

Stock Plan

Stock Plan	6 Months Ended
	Jul. 02, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock Plan	Stock Plan Equity Incentive Plans In May 2015, the Company’s board of directors and stockholders adopted and approved the 2015 Equity Incentive Plan, or 2015 Plan. The 2015 Plan became effective on June 16, 2015 and serves as the successor to the Amended and Restated 2007 Stock Plan, or 2007 Plan. The Company ceased granting awards under the 2007 Plan, and any outstanding stock options and restricted stock units, or RSUs, granted under the 2007 Plan will remain subject to the terms of the 2007 Stock Plan. As of July 2, 2016 , 8.3 million shares were reserved and available for future issuance under the 2015 Plan. Employee Stock Purchase Plan In May 2015, the Company’s board of directors adopted the 2015 Employee Stock Purchase Plan, or 2015 ESPP, which became effective on June 17, 2015. A total of 3.8 million shares of Class A common stock were initially reserved for issuance under the 2015 ESPP. The 2015 ESPP allows eligible employees to purchase shares of the Company’s Class A common stock through payroll deductions at a price per share equal to 85% of the lesser of the fair market value of the Company’s common stock (i) on the first trading day of the applicable offering period and (2) the last trading day of each purchase period in the applicable offering period. Except for the initial offering period, the 2015 ESPP provides for 6 -month offering periods beginning in May and November of each year. The initial offering period began June 17, 2015, and ended in May 2016. Stock Options Stock option activity under the equity incentive plans was as follows: Options Outstanding Number of Shares Subject to Options Weighted– Average Exercise Price Aggregate Intrinsic Value (in thousands) (in thousands) Balance—December 31, 2015 44,362 $ 3.20 Granted 955 14.06 Exercised (5,362 ) 0.89 Forfeited or canceled (1,578 ) 4.51 Balance—July 2, 2016 38,377 3.74 $ 343,154 Options exercisable—July 2, 2016 20,516 2.09 $ 215,055 Options vested and expected to vest—July 2, 2016 37,783 3.70 $ 339,241 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest as of July 2, 2016 were calculated as the difference between the exercise price of the options and the fair value of the Class A common stock of $12.48 as of July 1, 2016. Restricted Stock Units RSU activity under the equity incentive plans was as follows: RSUs Outstanding Weighted- Average Grant Date Fair Value (in thousands) Unvested balance—December 31, 2015 3,292 $ 34.27 Granted 6,967 14.28 Vested (243 ) 21.05 Forfeited or canceled (182 ) 19.80 Unvested balance—July 2, 2016 9,834 20.70 Stock-Based Compensation Expense Total stock-based compensation recognized was as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Cost of revenue $ 1,084 $ 825 $ 2,393 $ 1,271 Research and development 11,725 3,138 22,118 5,017 Sales and marketing 2,927 1,322 5,462 2,629 General and administrative 4,664 2,462 8,197 3,733 Total stock-based compensation expense $ 20,400 $ 7,747 $ 38,170 $ 12,650 As of July 2, 2016 , the total unrecognized compensation expense related to unvested options and RSUs, net of estimated forfeitures, was $232.9 million , which the Company expects to recognize over an estimated weighted average period of 3.2 years.

Income Taxes

Income Taxes	6 Months Ended
	Jul. 02, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Company is subject to income tax in the United States as well as other tax jurisdictions in which it conducts business. Earnings from non-U.S. activities are subject to local country income tax. The Company does not provide for federal income taxes on the undistributed earnings of its foreign subsidiaries as such earnings are to be reinvested indefinitely. For the three and six months ended July 2, 2016 , the Company recorded an expense for income taxes of $3.7 million and $13.6 million , respectively, for an effective tax rate of 36.8% and 43.8% , respectively. The effective tax rate for the six months ended July 2, 2016 is higher than the statutory federal tax rate primarily due to the effect of an out-of-period adjustment recorded in the three months ended April 2, 2016, a change in mix of income between U.S. and foreign jurisdictions, and unrecognized tax benefits. For the three and six months ended June 30, 2015 , the Company recorded an expense for income taxes of $17.0 million and $45.4 million , respectively, for an effective tax rate of 49.1% and 40.9% , respectively. The effective tax rate for the six months ended June 30, 2015 was higher than the statutory federal tax rate primarily due to certain permanent differences related to the change in fair value of the redeemable convertible preferred stock warrant liability and non-deductible stock-based compensation expense, partially offset by non-taxable income associated with contingent consideration from the FitStar acquisition and a permanent domestic production activities deduction. As of July 2, 2016 , the total amount of gross unrecognized tax benefits was $28.5 million , all of which would affect the effective tax rate if recognized. The Company does not have any tax positions as of July 2, 2016 for which it is reasonably possible the total amount of gross unrecognized tax benefits will increase or decrease within the following 12 months.

Net Income per Share Attributab

Net Income per Share Attributable to Common Stockholders	6 Months Ended
	Jul. 02, 2016
Earnings Per Share [Abstract]
Net Income per Share Attributable to Common Stockholders	Net Income per Share Attributable to Common Stockholders Basic and diluted net income per share attributable to common stockholders is presented in conformity with the two-class method required for participating securities. Prior to the Company’s IPO in June 2015, the Company considered its redeemable convertible preferred stock to be participating securities. In accordance with the two-class method, earnings allocated to these participating securities and the related number of outstanding shares of the participating securities, which include contractual participation rights in undistributed earnings, have been excluded from the computation of basic and diluted net income per share attributable to common stockholders. In connection with the IPO, the Company established two classes of authorized common stock: Class A common stock and Class B common stock. As a result, all then-outstanding shares of common stock were converted into shares of Class B common stock. The rights of the holders of Class A and Class B common stock are identical, except with respect to voting and conversion. Each share of Class A common stock is entitled to one vote per share and each share of Class B common stock is entitled to ten votes per share. Each share of Class B common stock is convertible at any time at the option of the stockholder into one share of Class A common stock, generally automatically converts into Class A common stock upon a transfer, and has no expiration date. The Company applies the two-class method of calculating earnings per share, but as the dividend rights of both classes are identical, basic and diluted earnings per share are the same for both classes. Undistributed earnings allocated to participating securities are subtracted from net income in determining net income attributable to common stockholders. Basic net income per share attributable to common stockholders is computed by dividing the net income attributable to common stockholders by the weighted-average number of common shares outstanding during the period. All participating securities are excluded from basic weighted-average common shares outstanding. For the calculation of diluted EPS, net income attributable to common stockholders for basic EPS is adjusted by the effect of dilutive securities. Diluted net income per share attributable to common stockholders is computed by dividing the net income attributable to common stockholders by the weighted-average number of common shares outstanding, including all potentially dilutive common shares, if the effect of such shares is dilutive. The following table sets forth the computation of the Company’s basic and diluted net income per share attributable to common stockholders (in thousands, except per share amounts): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Numerator: Net income $ 6,341 $ 17,681 $ 17,376 $ 65,678 Less: noncumulative dividends to preferred stockholders — (1,212 ) — (2,526 ) Less: undistributed earnings to participating securities — (11,244 ) — (45,907 ) Net income attributable to common stockholders—basic 6,341 5,225 17,376 17,245 Add: adjustments to undistributed earnings to participating securities — 1,862 — 7,003 Net income attributable to common stockholders—diluted $ 6,341 $ 7,087 $ 17,376 $ 24,248 Denominator: Weighted-average shares of common stock—basic for Class A and Class B 218,850 58,548 217,431 49,922 Effect of dilutive securities 23,478 36,642 24,722 32,919 Weighted-average shares of common stock—diluted for Class A and Class B 242,328 95,190 242,153 82,841 Net income per share attributable to common stockholders: Basic $ 0.03 $ 0.09 $ 0.08 $ 0.35 Diluted $ 0.03 $ 0.07 $ 0.07 $ 0.29 The following potentially dilutive common shares were excluded from the computation of diluted net income per share for the periods presented because including them would have been anti-dilutive (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Stock options to purchase common stock 3,861 — 3,548 799 Restricted stock units 4,256 — 3,884 — Redeemable convertible preferred stock — 126,020 — 132,898 Redeemable convertible preferred stock warrants — 1,808 — 1,808 Total 8,117 127,828 7,432 135,505

Significant Customer Informatio

Significant Customer Information and Other Information	6 Months Ended
	Jul. 02, 2016
Risks and Uncertainties [Abstract]
Significant Customer Information and Other Information	Significant Customer Information and Other Information Retailer and Distributor Concentration Retailers and distributors with revenue equal to or greater than 10% of total revenue for the three and six months ended July 2, 2016 and June 30, 2015 were as follows: Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 A 16 % 14 % 17 % 16 % C 14 13 13 12 B 14 14 12 12 Retailers and distributors that accounted for equal to or greater than 10% of accounts receivable at July 2, 2016 and December 31, 2015 were as follows: July 2, December 31, A 23 % 15 % B 18 19 C 15 23 Geographic and Other Information Revenue by geographic region, based on ship-to destinations, was as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 United States $ 445,192 $ 312,666 $ 796,877 $ 577,975 Americas excluding United States 27,375 16,799 50,769 30,228 Europe, Middle East, and Africa 99,471 39,712 174,195 74,768 APAC 14,490 31,235 70,043 54,195 Total $ 586,528 $ 400,412 $ 1,091,884 $ 737,166 As of July 2, 2016 and December 31, 2015 , long-lived assets, which represent property and equipment, located outside the United States were $42.6 million and $28.9 million , respectively.

Acquisition

Acquisition	6 Months Ended
	Jul. 02, 2016
Business Combinations [Abstract]
Acquisition	Acquisitions 2016 Acquisitions In May 2016, the Company completed a purchase of certain assets from a privately-held company, which was accounted for as a business combination, for total cash consideration of $7.0 million , of which $3.9 million was allocated to in-process research and development intangible assets, and $3.1 million to goodwill. This acquisition was not material to the Company’s condensed consolidated financial statements. FitStar Acquisition — 2015 In March 2015, the Company acquired all of the outstanding securities of FitStar, a privately-held company, for aggregate acquisition consideration of $32.5 million , comprised of $13.3 million related to the issuance of 1,059,688 shares of the Company’s Class B common stock, $11.5 million of cash, and $7.7 million of contingent consideration. FitStar is a provider of interactive video-based exercise experiences on mobile devices and computers that utilize proprietary algorithms to adjust and customize workouts for individual users. The acquisition is expected to enhance the Company’s software and services offerings. Under the acquisition agreement, the Company was obligated to issue additional common stock or pay cash to FitStar stockholders. The actual amount of any contingent consideration depended on market-based events that may occur in the future. The Company determined the fair market value of this contingent consideration to be $7.7 million as of the acquisition date using the Monte Carlo simulation method. The fair value of this liability was adjusted at each reporting period, and the change in fair value is included in total operating expenses on the condensed consolidated statements of operations. As a result of the Company’s IPO, the Company recorded a change in fair value of $7.7 million as a benefit and as of December 31, 2015, the fair value of the contingent consideration liability was zero . In addition, the terms related to the contingent consideration expired as of December 31, 2015 and no amounts were paid or shares issued for the contingent consideration. The following table summarizes the fair value of assets acquired and liabilities assumed (in thousands): Goodwill $ 22,157 Developed and core technology 12,640 Customer relationships 128 Trademarks 1,150 Assumed liabilities, net of assets (3,552 ) Total $ 32,523 The amortization periods of the acquired developed technology, customer relationships, and trademarks are 7.0 years , 1.3 years , and 5.0 years , respectively. Goodwill is not deductible for tax purposes. In addition, upon acquisition, the Company issued 308,216 additional shares of common stock valued at $4.2 million . The Company is also obligated to make cash payments up to $1.2 million . Both the common stock and the cash payments are additional consideration which is contingent upon former employees of FitStar continuing to be employed by the Company. As such, this additional consideration was not part of the purchase price and is recognized as post-acquisition compensation expense over the related requisite service period of 3 years . The Company also recorded acquisition-related transaction costs of $0.3 million , which were included in general and administrative expenses in the condensed consolidated statements of operations during the six months ended June 30, 2015. The results of operations of both acquisitions are included in the accompanying condensed consolidated statements of operations from the date of acquisition. Pro forma and historical results of operations for both acquisitions have not been presented because they are not material, either individually or in the aggregate, to the Company’s condensed consolidated financial statements.

Basis of Presentation and Sum18

Basis of Presentation and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jul. 02, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation and Summary of Significant Accounting Policies	The accompanying condensed consolidated financial statements are unaudited. The condensed consolidated balance sheet at December 31, 2015 has been derived from the audited financial statements of the Company. The accompanying condensed financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America, or U.S. GAAP, for interim financial information, and in management’s opinion, includes all adjustments, consisting of only normal recurring adjustments, necessary for the fair statement of the Company’s financial position, its results of operations, and cash flows for the interim periods presented. The results of operations for the three and six months ended July 2, 2016 are not necessarily indicative of the results to be expected for the full fiscal year or any other period. The accompanying condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and notes thereto contained in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2015, filed with the Securities and Exchange Commission on February 29, 2016. There have been no significant changes in the Company’s accounting policies from those disclosed in its Annual Report on Form 10-K. The Company’s fiscal year ends on December 31 of each year. In the first quarter of 2016, the Company adopted a 4-4-5 week quarterly calendar, which, for the 2016 fiscal year, is comprised of four fiscal quarters ending on April 2, 2016, July 2, 2016, October 1, 2016 and December 31, 2016. The Company did not adjust operating results for quarters prior to 2016. There were 91 days in each of the three months ended July 2, 2016 and June 30, 2015 , and 184 and 181 days in the six months ended July 2, 2016 and June 30, 2015 , respectively.
Principles of Consolidation	The condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in accordance with U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported and disclosed in the condensed consolidated financial statements and accompanying notes. The primary estimates and assumptions made by management related to revenue recognition, reserves for sales returns and incentives, reserves for warranty, valuation of stock options, fair value of derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, accruals for the Fitbit Force recall, fair value of goodwill and acquired tangible and intangible assets and liabilities assumed during acquisitions, the number of reporting segments, the recoverability of intangible assets and their useful lives, contingencies, and the valuations of deferred income tax assets and uncertain tax positions. Actual results could differ from those estimates, and such differences may be material to the condensed consolidated financial statements.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board, or FASB, issued ASU 2014-09 (ASC 606), Revenue from Contracts with Customers , which affects any entity that either enters into contracts with customers to transfer goods and services or enters into contracts for the transfer of nonfinancial assets. ASU 2014-09 will replace most existing revenue recognition guidance in U.S. GAAP when it becomes effective. 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 currently effective 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. In July 2015, the FASB approved a one-year deferral of the effective date of the standard. ASU 2014-09 will become effective for the Company on January 1, 2018 and can be adopted either retrospectively to each prior reporting period presented or as a cumulative effect adjustment as of the date of adoption. Early adoption is permitted but not before the original effective date of annual periods beginning after December 15, 2016. In April 2016, the FASB issued ASU 2016-10, which clarifies guidance on identifying performance obligations and licensing implementation. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In February 2016, the FASB issued ASU 2016-02, Leases . This ASU requires lease assets and lease liabilities arising from leases, including operating leases, to be recognized on the balance sheet. ASU 2016-02 will become effective for the Company on January 1, 2019, and requires adoption using a modified retrospective approach. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In March 2016, the FASB issued ASU 2016-09, Compensation — Stock Compensation (Topic 718). This ASU simplifies several aspects of the accounting for share-based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. ASU 2016-09 will become effective for the Company on January 1, 2017 and early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements. In June 2016, the FASB issued ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. This ASU provides for a new impairment model which requires measurement and recognition of expected credit losses for most financial assets and certain other instruments. ASU 2016-13 will become effective for the Company on January 1, 2020 and early adoption is permitted. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jul. 02, 2016
Fair Value Disclosures [Abstract]
Schedule of fair value of assets and liabilities measured on recurring basis	The following tables set forth the Company’s financial instruments that were measured at fair value on a recurring basis by level within the fair value hierarchy (in thousands): July 2, 2016 Level 1 Level 2 Total Assets: Money market funds $ 162,633 $ — $ 162,633 U.S. government agencies — 68,834 68,834 Corporate debt securities — 384,429 384,429 Derivative assets — 9,134 9,134 Total $ 162,633 $ 462,397 $ 625,030 Liabilities: Derivative liabilities $ — $ 5,964 $ 5,964 December 31, 2015 Level 1 Level 2 Total Assets: Money market funds $ 248,128 $ — $ 248,128 U.S. government agencies — 113,314 113,314 Corporate debt securities — 193,964 193,964 Derivative assets — 6,002 6,002 Total $ 248,128 $ 313,280 $ 561,408 Liabilities: Derivative liabilities $ — $ 2,640 $ 2,640

Financial Instruments (Tables)

Financial Instruments (Tables)	6 Months Ended
	Jul. 02, 2016
Investments, Debt and Equity Securities [Abstract]
Schedule of available for sale securities including fair value and gross unrealized losses	The following table sets forth cash, cash equivalents, and marketable securities as of July 2, 2016 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 143,780 $ — $ — $ 143,780 $ 143,780 $ — Money market funds 162,633 — — 162,633 162,633 — U.S. government agencies 68,767 67 — 68,834 — 68,834 Corporate debt securities 384,425 36 (32 ) 384,429 109,729 274,700 Total $ 759,605 $ 103 $ (32 ) $ 759,676 $ 416,142 $ 343,534 The following table sets forth cash, cash equivalents, and marketable securities as of December 31, 2015 (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Cash and Cash Equivalents Marketable Securities Cash $ 109,072 $ — $ — $ 109,072 $ 109,072 $ — Money market funds 248,128 — — 248,128 248,128 — U.S. government agencies 113,315 3 (4 ) 113,314 63,464 49,850 Corporate debt securities 194,018 1 (55 ) 193,964 115,182 78,782 Total $ 664,533 $ 4 $ (59 ) $ 664,478 $ 535,846 $ 128,632 The following table classifies marketable securities by contractual maturities (in thousands): July 2, 2016 December 31, 2015 Due in one year $ 341,041 $ 128,632 Due in one to two years 2,493 — Total $ 343,534 $ 128,632
Schedule of derivative instruments in statement of financial position, fair value	The following table presents the fair value of the Company’s foreign currency derivative contracts as of the periods presented (in thousands): July 2, 2016 December 31, 2015 Balance Sheet Location Fair Value Derivative Assets Fair Value Derivative Liabilities Fair Value Derivative Assets Fair Value Derivative Liabilities Cash flow designated hedges Prepaid expenses and other current assets $ 5,211 $ — $ 3,116 $ — Cash flow designated hedges Accrued liabilities — 3,101 — 1,327 Hedges not designated Prepaid expenses and other current assets 3,923 — 2,886 — Hedges not designated Accrued liabilities — 2,863 — 1,313 Total fair value of derivative instruments $ 9,134 $ 5,964 $ 6,002 $ 2,640
Schedule of cash flow hedging instruments, statement of operations	The following table presents the pre-tax impact of the Company’s foreign currency derivative contracts on other comprehensive income, or OCI, and the condensed consolidated statements of operations for the periods presented (in thousands): Three Months Ended Six Months Ended Income Statement Location July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Foreign exchange cash flow hedges Gain (loss) recognized in OCI – effective portion $ 5,783 $ — $ 1,535 $ — Gain (loss) reclassified from OCI into income – effective portion Revenue (1,380 ) — (1,550 ) — Gain (loss) reclassified from OCI into income – effective portion Operating expenses 1,393 — 2,408 — Gain (loss) recognized in income – ineffective portion Other income (expense), net (95 ) — (185 ) — Foreign exchange balance sheet hedges Gain (loss) recognized in income Other income (expense), net $ (72 ) $ 434 $ (209 ) $ 2,454
Schedule of cash flow hedging instruments, comprehensive income	The following table presents the pre-tax impact of the Company’s foreign currency derivative contracts on other comprehensive income, or OCI, and the condensed consolidated statements of operations for the periods presented (in thousands): Three Months Ended Six Months Ended Income Statement Location July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Foreign exchange cash flow hedges Gain (loss) recognized in OCI – effective portion $ 5,783 $ — $ 1,535 $ — Gain (loss) reclassified from OCI into income – effective portion Revenue (1,380 ) — (1,550 ) — Gain (loss) reclassified from OCI into income – effective portion Operating expenses 1,393 — 2,408 — Gain (loss) recognized in income – ineffective portion Other income (expense), net (95 ) — (185 ) — Foreign exchange balance sheet hedges Gain (loss) recognized in income Other income (expense), net $ (72 ) $ 434 $ (209 ) $ 2,454
Schedule of offsetting of foreign currency derivative contracts	The following tables set forth the available offsetting of net derivative assets under the master netting arrangements as of July 2, 2016 and December 31, 2015 (in thousands): As of July 2, 2016 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Received Net Amount Foreign exchange contracts $ 9,134 $ — $ 9,134 $ 4,960 $ — $ 4,174 As of December 31, 2015 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Received Net Amount Foreign exchange contracts $ 6,002 $ — $ 6,002 $ 2,100 $ — $ 3,902 The following tables set forth the available offsetting of net derivative liabilities under the master netting arrangements as of July 2, 2016 and December 31, 2015 (in thousands): As of July 2, 2016 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Pledged Net Amount Foreign exchange contracts $ 5,964 $ — $ 5,964 $ 4,960 $ — $ 1,004 As of December 31, 2015 Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Pledged Net Amount Foreign exchange contracts $ 2,640 $ — $ 2,640 $ 2,100 $ — $ 540

Balance Sheet Components (Table

Balance Sheet Components (Tables)	6 Months Ended
	Jul. 02, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of accounts receivable reserves	Revenue returns reserve activities were as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 55,875 $ 26,362 $ 74,045 $ 26,559 Increases 85,335 32,859 119,550 53,352 Returns taken (60,933 ) (23,956 ) (113,318 ) (44,646 ) Ending balances $ 80,277 $ 35,265 $ 80,277 $ 35,265
Schedule of inventories	Inventories consisted of the following (in thousands): July 2, 2016 December 31, 2015 Components $ 1,699 $ 5,359 Finished goods 188,945 172,787 Total inventories $ 190,644 $ 178,146
Schedule of prepaid expenses and other current asset	Prepaid expenses and other current assets consisted of the following (in thousands): July 2, 2016 December 31, 2015 POP displays, net $ 23,801 $ 9,990 Derivative assets 9,134 6,002 Prepaid income taxes 638 11,889 Prepaid expenses and other current assets 26,209 15,649 Total prepaid expenses and other current assets $ 59,782 $ 43,530
Schedule of property and equipment	Property and equipment, net, consisted of the following (in thousands): July 2, 2016 December 31, 2015 Tooling and manufacturing equipment $ 74,198 $ 53,092 Furniture and office equipment 8,483 6,809 Purchased and internally-developed software 6,770 3,794 Leasehold improvements 22,010 8,388 Total property and equipment 111,461 72,083 Less: Accumulated depreciation and amortization (37,280 ) (27,582 ) Property and equipment, net $ 74,181 $ 44,501
Schedule of intangible assets (excluding goodwill)	The carrying amounts of the intangible assets as of July 2, 2016 and December 31, 2015 were as follows (in thousands, except useful life). In-process research and development is not amortized until the completion of the related development. July 2, 2016 December 31, 2015 Weighted Average Remaining Useful Life (years) Gross Accumulated Amortization Net Gross Accumulated Amortization Net Developed technology $ 12,640 $ (2,345 ) $ 10,295 $ 12,640 $ (1,442 ) $ 11,198 5.8 Trademarks and other 1,278 (423 ) 855 1,278 (260 ) 1,018 3.7 Total finite-lived intangible assets subject to amortization, net 13,918 (2,768 ) 11,150 13,918 (1,702 ) 12,216 In-process research and development 3,940 — 3,940 — — — Total intangible assets, net $ 17,858 $ (2,768 ) $ 15,090 $ 13,918 $ (1,702 ) $ 12,216
Schedule of estimated future amortization expense	The estimated future amortization expense of acquired finite-lived intangible assets to be charged to cost of revenue and operating expenses after July 2, 2016 , is as follows (in thousands): Cost of Revenue Operating Expenses Total Remaining 2016 $ 903 $ 118 $ 1,021 2017 1,806 230 2,036 2018 1,806 230 2,036 2019 1,806 230 2,036 2020 1,806 47 1,853 Thereafter 2,168 — 2,168 Total finite-lived intangible assets, net $ 10,295 $ 855 $ 11,150
Schedule of accrued liabilities	Accrued liabilities consisted of the following (in thousands): July 2, 2016 December 31, 2015 Product warranty $ 76,841 $ 40,212 Accrued sales and marketing 45,736 33,389 Employee related liabilities 23,421 27,394 Accrued co-op advertising and marketing development funds 18,879 29,077 Accrued sales incentives 17,670 24,324 Accrued manufacturing expense and freight 12,982 10,723 Inventory received but not billed 6,759 4,292 Derivative liabilities 5,964 2,640 Sales taxes and VAT payable 5,753 8,349 Accrued legal fees 3,326 3,138 Customer deposits 1,006 2,062 Other 13,584 9,377 Accrued liabilities $ 231,921 $ 194,977
Schedule of product warranty reserves	Product warranty reserve activities were as follows (in thousands) (1) : Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 50,669 $ 23,251 $ 40,212 $ 20,098 Charged to cost of revenue 50,480 14,568 78,024 22,065 Settlement of claims (24,308 ) (6,756 ) (41,395 ) (11,100 ) Ending balances $ 76,841 $ 31,063 $ 76,841 $ 31,063 (1) Does not include reserves established as a result of the recall of the Fitbit Force. See the section titled “—Fitbit Force Recall Reserve” for additional information regarding such reserves.
Schedule of product recall reserves	Fitbit Force Recall reserve activities were as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Beginning balances $ 4,339 $ 15,104 $ 5,122 $ 22,476 Charged (benefit) to cost of revenue — — — (2,040 ) Charged (benefit) to general and administrative — 69 — (73 ) Settlement of claims (2,191 ) (2,279 ) (2,974 ) (7,469 ) Ending balances $ 2,148 $ 12,894 $ 2,148 $ 12,894
Schedule of accumulated other comprehensive income	The components and activity of accumulated other comprehensive income, or AOCI, net of tax, were as follows (in thousands): Unrealized Gains (Losses) on Cash Flow Hedges Currency Translation Adjustments Unrealized Gains (Losses) on Available-for-Sale Investments Total Balance at December 31, 2015 $ 751 $ (5 ) $ (55 ) $ 691 Other comprehensive income (loss) before reclassifications 3,005 (160 ) 126 2,971 Amounts reclassified from AOCI (1,978 ) — — (1,978 ) Other comprehensive income (loss) 1,027 (160 ) 126 993 Balance at July 2, 2016 $ 1,778 $ (165 ) $ 71 $ 1,684

Stock Plan (Tables)

Stock Plan (Tables)	6 Months Ended
	Jul. 02, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock option activity	Stock option activity under the equity incentive plans was as follows: Options Outstanding Number of Shares Subject to Options Weighted– Average Exercise Price Aggregate Intrinsic Value (in thousands) (in thousands) Balance—December 31, 2015 44,362 $ 3.20 Granted 955 14.06 Exercised (5,362 ) 0.89 Forfeited or canceled (1,578 ) 4.51 Balance—July 2, 2016 38,377 3.74 $ 343,154 Options exercisable—July 2, 2016 20,516 2.09 $ 215,055 Options vested and expected to vest—July 2, 2016 37,783 3.70 $ 339,241
Schedule of restricted stock unit activity	RSU activity under the equity incentive plans was as follows: RSUs Outstanding Weighted- Average Grant Date Fair Value (in thousands) Unvested balance—December 31, 2015 3,292 $ 34.27 Granted 6,967 14.28 Vested (243 ) 21.05 Forfeited or canceled (182 ) 19.80 Unvested balance—July 2, 2016 9,834 20.70
Schedule of stock-based compensation expense	Total stock-based compensation recognized was as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Cost of revenue $ 1,084 $ 825 $ 2,393 $ 1,271 Research and development 11,725 3,138 22,118 5,017 Sales and marketing 2,927 1,322 5,462 2,629 General and administrative 4,664 2,462 8,197 3,733 Total stock-based compensation expense $ 20,400 $ 7,747 $ 38,170 $ 12,650

Net Income per Share Attribut23

Net Income per Share Attributable to Common Stockholders (Tables)	6 Months Ended
	Jul. 02, 2016
Earnings Per Share [Abstract]
Schedule of basic and diluted net income (loss) per share	The following table sets forth the computation of the Company’s basic and diluted net income per share attributable to common stockholders (in thousands, except per share amounts): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Numerator: Net income $ 6,341 $ 17,681 $ 17,376 $ 65,678 Less: noncumulative dividends to preferred stockholders — (1,212 ) — (2,526 ) Less: undistributed earnings to participating securities — (11,244 ) — (45,907 ) Net income attributable to common stockholders—basic 6,341 5,225 17,376 17,245 Add: adjustments to undistributed earnings to participating securities — 1,862 — 7,003 Net income attributable to common stockholders—diluted $ 6,341 $ 7,087 $ 17,376 $ 24,248 Denominator: Weighted-average shares of common stock—basic for Class A and Class B 218,850 58,548 217,431 49,922 Effect of dilutive securities 23,478 36,642 24,722 32,919 Weighted-average shares of common stock—diluted for Class A and Class B 242,328 95,190 242,153 82,841 Net income per share attributable to common stockholders: Basic $ 0.03 $ 0.09 $ 0.08 $ 0.35 Diluted $ 0.03 $ 0.07 $ 0.07 $ 0.29
Schedule of antidilutive securities excluded from earnings per share	The following potentially dilutive common shares were excluded from the computation of diluted net income per share for the periods presented because including them would have been anti-dilutive (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 Stock options to purchase common stock 3,861 — 3,548 799 Restricted stock units 4,256 — 3,884 — Redeemable convertible preferred stock — 126,020 — 132,898 Redeemable convertible preferred stock warrants — 1,808 — 1,808 Total 8,117 127,828 7,432 135,505

Significant Customer Informat24

Significant Customer Information and Other Information (Tables)	6 Months Ended
	Jul. 02, 2016
Risks and Uncertainties [Abstract]
Schedules of concentration of risk	Revenue by geographic region, based on ship-to destinations, was as follows (in thousands): Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 United States $ 445,192 $ 312,666 $ 796,877 $ 577,975 Americas excluding United States 27,375 16,799 50,769 30,228 Europe, Middle East, and Africa 99,471 39,712 174,195 74,768 APAC 14,490 31,235 70,043 54,195 Total $ 586,528 $ 400,412 $ 1,091,884 $ 737,166 Retailers and distributors with revenue equal to or greater than 10% of total revenue for the three and six months ended July 2, 2016 and June 30, 2015 were as follows: Three Months Ended Six Months Ended July 2, 2016 June 30, 2015 July 2, 2016 June 30, 2015 A 16 % 14 % 17 % 16 % C 14 13 13 12 B 14 14 12 12 Retailers and distributors that accounted for equal to or greater than 10% of accounts receivable at July 2, 2016 and December 31, 2015 were as follows: July 2, December 31, A 23 % 15 % B 18 19 C 15 23

Acquisition (Tables)

Acquisition (Tables)	6 Months Ended
	Jul. 02, 2016
Business Combinations [Abstract]
Schedule of fair value of assets acquired and liabilities assumed	The following table summarizes the fair value of assets acquired and liabilities assumed (in thousands): Goodwill $ 22,157 Developed and core technology 12,640 Customer relationships 128 Trademarks 1,150 Assumed liabilities, net of assets (3,552 ) Total $ 32,523

Basis of Presentation and Sum26

Basis of Presentation and Summary of Significant Accounting Policies - Out of Period Adjustments (Details) $ in Millions	3 Months Ended
	Apr. 02, 2016USD ($)
Understated Income Tax Expense [Member]
Quantifying Misstatement in Current Year Financial Statements [Line Items]
Out-of-period adjustment	$ 3

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($)	Jul. 02, 2016	Dec. 31, 2015
Assets:
Available for sale securities	$ 343,534,000	$ 128,632,000
Liabilities:
Derivative liabilities	5,964,000	2,640,000
U.S. government agencies [Member]
Assets:
Available for sale securities	68,834,000	49,850,000
Corporate debt securities [Member]
Assets:
Available for sale securities	274,700,000	78,782,000
Fair Value, Measurements, Recurring [Member]
Assets:
Money market funds	162,633,000	248,128,000
Derivative assets	9,134,000	6,002,000
Total	625,030,000	561,408,000
Liabilities:
Derivative liabilities	5,964,000	2,640,000
Fair Value, Measurements, Recurring [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	68,834,000	113,314,000
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	384,429,000	193,964,000
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Money market funds	162,633,000	248,128,000
Derivative assets	0	0
Total	162,633,000	248,128,000
Liabilities:
Derivative liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	0	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Money market funds	0	0
Derivative assets	9,134,000	6,002,000
Total	462,397,000	313,280,000
Liabilities:
Derivative liabilities	5,964,000	2,640,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	68,834,000	113,314,000
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	384,429,000	193,964,000
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
Total	0	0
Liabilities:
Derivative liabilities	$ 0	$ 0

Financial Instruments - Amortiz

Financial Instruments - Amortized to fair value (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jul. 02, 2016	Dec. 31, 2015	Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Impairment losses recorded on available-for-sale securities	$ 0	$ 0
Cash and cash equivalents	416,142,000	535,846,000	$ 461,276,000	$ 195,626,000
Available-for-sale debt securities, gross unrealized gains	103,000	4,000
Available-for-sale debt securities, gross unrealized losses	(32,000)	(59,000)
Cash, cash equivalents, and available-for-sale securities, amortized cost	759,605,000	664,533,000
Cash, cash equivalents, available-for-sale securities, fair value	759,676,000	664,478,000
Total	343,534,000	128,632,000
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents		63,464,000
Available-for-sale debt securities, amortized cost	68,767,000	113,315,000
Available-for-sale debt securities, gross unrealized gains	67,000	3,000
Available-for-sale debt securities, gross unrealized losses		(4,000)
Cash, cash equivalents, available-for-sale securities, fair value	68,834,000	113,314,000
Total	68,834,000	49,850,000
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	109,729,000	115,182,000
Available-for-sale debt securities, amortized cost	384,425,000	194,018,000
Available-for-sale debt securities, gross unrealized gains	36,000	1,000
Available-for-sale debt securities, gross unrealized losses	(32,000)	(55,000)
Cash, cash equivalents, available-for-sale securities, fair value	384,429,000	193,964,000
Total	274,700,000	78,782,000
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	143,780,000	109,072,000
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 162,633,000	$ 248,128,000

Financial Instruments - Contrac

Financial Instruments - Contractual maturity dates (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]
Due in one year	$ 341,041	$ 128,632
Due in one to two years	2,493	0
Total	$ 343,534	$ 128,632

Financial Instruments - Unreali

Financial Instruments - Unrealized Loss Position (Details) - USD ($)	6 Months Ended	12 Months Ended
	Jul. 02, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Available-for-sale securities in continuous loss position for one year or more, gross unrealized losses	$ 0	$ 0
Gross unrealized gains (losses)	$ 0	$ 0

Financial Instruments - Additio

Financial Instruments - Additional Derivative Information (Details) - Foreign currency exchange contract [Member] - USD ($) $ in Millions	Jul. 02, 2016	Dec. 31, 2015
Not designated as hedging instrument [Member]
Derivative [Line Items]
Derivative, notional amount	$ 104.3	$ 104.8
Cash flow hedges [Member] | Designated as hedging instrument [Member]
Derivative [Line Items]
Derivative, notional amount based on forecasted revenue	246.9	$ 254.1
Derivative, notional amount based on forecasted expenses	$ 50.8

Financial Instruments - Financi

Financial Instruments - Financial Position, Fair Value (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Fair Value Derivative Liabilities	$ 5,964	$ 2,640
Foreign currency exchange contract [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	9,134	6,002
Fair Value Derivative Liabilities	5,964	2,640
Foreign currency exchange contract [Member] | Designated as hedging instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	5,211	3,116
Fair Value Derivative Liabilities	0	0
Foreign currency exchange contract [Member] | Designated as hedging instrument [Member] | Accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	0	0
Fair Value Derivative Liabilities	3,101	1,327
Foreign currency exchange contract [Member] | Not designated as hedging instrument [Member] | Prepaid expenses and other current assets [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	3,923	2,886
Fair Value Derivative Liabilities	0	0
Foreign currency exchange contract [Member] | Not designated as hedging instrument [Member] | Accrued liabilities [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	0	0
Fair Value Derivative Liabilities	$ 2,863	$ 1,313

Financial Instruments - Stateme

Financial Instruments - Statement of Operations and Other Comprehensive Income (Details) - Foreign currency exchange contract [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Designated as hedging instrument [Member] | Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in OCI – effective portion	$ 5,783	$ 0	$ 1,535	$ 0
Revenue [Member] | Designated as hedging instrument [Member] | Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from OCI into income – effective portion	(1,380)	0	(1,550)	0
Operating expenses [Member] | Designated as hedging instrument [Member] | Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) reclassified from OCI into income – effective portion	1,393	0	2,408	0
Other Income (Expense), Net [Member] | Designated as hedging instrument [Member] | Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in income – ineffective portion	(95)	0	(185)	0
Other Income (Expense), Net [Member] | Not designated as hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in income	$ (72)	$ 434	$ (209)	$ 2,454

Financial Instruments - Offsett

Financial Instruments - Offsetting of Foreign Currency Derivative Contracts (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Offsetting Liabilities [Line Items]
Fair Value Derivative Liabilities	$ 5,964	$ 2,640
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Derivative liabilities	5,964	2,640
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	4,960	2,100
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Pledged	0	0
Net Amount	1,004	540
Foreign currency exchange contract [Member]
Offsetting Liabilities [Line Items]
Fair Value Derivative Liabilities	5,964	2,640
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	9,134	6,002
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0	0
Net Amounts Presented in Condensed Consolidated Balance Sheets	9,134	6,002
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	4,960	2,100
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Received	0	0
Net Amount	$ 4,174	$ 3,902

Balance Sheet Components - Acco

Balance Sheet Components - Account Receivable Reserves (Details) - Revenue Reserve [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balances	$ 55,875	$ 26,362	$ 74,045	$ 26,559
Increases	85,335	32,859	119,550	53,352
Returns taken	(60,933)	(23,956)	(113,318)	(44,646)
Ending balances	$ 80,277	$ 35,265	$ 80,277	$ 35,265

Balance Sheet Components - Inve

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Components	$ 1,699	$ 5,359
Finished goods	188,945	172,787
Total inventories	$ 190,644	$ 178,146

Balance Sheet Components - Prep

Balance Sheet Components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
POP displays, net	$ 23,801	$ 9,990
Derivative assets	9,134	6,002
Prepaid income taxes	638	11,889
Prepaid expenses and other current assets	26,209	15,649
Total prepaid expenses and other current assets	$ 59,782	$ 43,530

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 111,461	$ 72,083
Less: Accumulated depreciation and amortization	(37,280)	(27,582)
Property and equipment, net	74,181	44,501
Tooling and manufacturing equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	74,198	53,092
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	8,483	6,809
Purchased and internally-developed software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,770	3,794
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 22,010	$ 8,388

Balance Sheet Components - Good

Balance Sheet Components - Goodwill (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Goodwill [Roll Forward]
Goodwill	$ 25,217	$ 22,157

Balance Sheet Components - Inta

Balance Sheet Components - Intangible Assets (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross	$ 13,918		$ 13,918		$ 13,918
Accumulated Amortization	(2,768)		(2,768)		(1,702)
Intangible assets, net	15,090		15,090		12,216
Net	11,150		11,150		12,216
Intangible Assets, Gross (Excluding Goodwill)	17,858		17,858		13,918
Amortization of intangible assets	500	$ 500	1,066	$ 655
Developed technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	12,640		12,640		12,640
Accumulated Amortization	(2,345)		(2,345)		(1,442)
Net	10,295		$ 10,295		11,198
Weighted Average Remaining Useful Life (years)			5 years 9 months
Trademarks and other [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	1,278		$ 1,278		1,278
Accumulated Amortization	(423)		(423)		(260)
Net	855		$ 855		1,018
Weighted Average Remaining Useful Life (years)			3 years 8 months 20 days
In Process Research and Development [Member]
Finite-Lived Intangible Assets [Line Items]
Indefinite-Lived Intangible Assets (Excluding Goodwill)	$ 3,940		$ 3,940		$ 0

Balance Sheet Components - Esti

Balance Sheet Components - Estimated Future Amortization Expense (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Remaining 2,016	$ 1,021
2,017	2,036
2,018	2,036
2,019	2,036
2,020	1,853
Thereafter	2,168
Net	11,150	$ 12,216
Cost of revenue [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2,016	903
2,017	1,806
2,018	1,806
2,019	1,806
2,020	1,806
Thereafter	2,168
Net	10,295
Operating expenses [Member]
Finite-Lived Intangible Assets [Line Items]
Remaining 2,016	118
2,017	230
2,018	230
2,019	230
2,020	47
Thereafter	0
Net	$ 855

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Product warranty	$ 76,841	$ 40,212
Accrued sales and marketing	45,736	33,389
Employee related liabilities	23,421	27,394
Accrued co-op advertising and marketing development funds	18,879	29,077
Accrued sales incentives	17,670	24,324
Accrued manufacturing expense and freight	12,982	10,723
Inventory received but not billed	6,759	4,292
Derivative liabilities	5,964	2,640
Sales taxes and VAT payable	5,753	8,349
Accrued legal fees	3,326	3,138
Customer deposits	1,006	2,062
Other	13,584	9,377
Accrued liabilities	$ 231,921	$ 194,977

Balance Sheet Components - Prod

Balance Sheet Components - Product Warranty (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Movement in Standard and Extended Product Warranty, Increase (Decrease) [Roll Forward]
Beginning balances	$ 50,669	$ 23,251	$ 40,212	$ 20,098
Charged to cost of revenue	50,480	14,568	78,024	22,065
Settlement of claims	(24,308)	(6,756)	(41,395)	(11,100)
Ending balances	$ 76,841	$ 31,063	$ 76,841	$ 31,063

Balance Sheet Components - Rese

Balance Sheet Components - Reserve Accounts (Details) - Product Recall Reserves [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balances	$ 4,339	$ 15,104	$ 5,122	$ 22,476
Charged (benefit) to cost of revenue	0	0	0	(2,040)
Charged (benefit) to general and administrative	0	69	0	(73)
Settlement of claims	(2,191)	(2,279)	(2,974)	(7,469)
Ending balances	$ 2,148	$ 12,894	$ 2,148	$ 12,894

Balance Sheet Components - Accu

Balance Sheet Components - Accumulated Other Comprehensive Income (Details) $ in Thousands	6 Months Ended
	Jul. 02, 2016USD ($)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015	$ 981,451
Balance at July 2, 2016	1,066,657
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015	751
Other comprehensive income (loss) before reclassifications	3,005
Amounts reclassified from AOCI	(1,978)
Other comprehensive income (loss)	1,027
Balance at July 2, 2016	1,778
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015	(5)
Other comprehensive income (loss) before reclassifications	(160)
Amounts reclassified from AOCI	0
Other comprehensive income (loss)	(160)
Balance at July 2, 2016	(165)
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015	(55)
Other comprehensive income (loss) before reclassifications	126
Amounts reclassified from AOCI	0
Other comprehensive income (loss)	126
Balance at July 2, 2016	71
AOCI Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2015	691
Other comprehensive income (loss) before reclassifications	2,971
Amounts reclassified from AOCI	(1,978)
Other comprehensive income (loss)	993
Balance at July 2, 2016	$ 1,684

Long-Term Debt (Details)

Long-Term Debt (Details)	12 Months Ended
	Dec. 31, 2015USD ($)	Jul. 02, 2016USD ($)	Jun. 30, 2015	Oct. 31, 2014USD ($)	Aug. 31, 2014USD ($)
Line of Credit [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity	$ 250,000,000
Credit facility, minimal stated interest rate	3.25%
Credit facility, minimum fixed charge coverage ratio	1.15
Credit facility, amount outstanding		$ 0
Line of Credit [Member] | 2015 Credit Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate	1.00%
Line of Credit [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity					$ 180,000,000
Revolving Credit Facility [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, minimum leverage ratio	3
Revolving Credit Facility [Member] | 2015 Credit Agreement [Member] | Federal Funds Effective Rate [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate	0.50%
Revolving Credit Facility [Member] | 2015 Credit Agreement [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate	1.00%
Revolving Credit Facility [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, effective interest rate			4.25%
Revolving Credit Facility [Member] | 2014 Revolving Credit And Guarantee Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity				$ 50,000,000
Credit facility, effective interest rate			3.59%
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility, amount outstanding	$ 17,100,000	$ 37,900,000
Letter of Credit [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity	50,000,000
Letter of Credit [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity					50,000,000
Letter of Credit [Member] | 2014 Revolving Credit And Guarantee Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity				10,000,000
Swing Line Loan [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity	$ 25,000,000
Swing Line Loan [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity					$ 25,000,000
Swing Line Loan [Member] | 2014 Revolving Credit And Guarantee Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity				$ 10,000,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Millions	May 19, 2016researcher	May 10, 2016investor	Jul. 07, 2015patent	Jul. 03, 2015patent	Jun. 10, 2015patent	Feb. 16, 2016lawsuit	Dec. 31, 2014lawsuit	Jul. 02, 2016USD ($)
Loss Contingencies [Line Items]
Future minimum payments under leases | $								$ 309.9
Loss contingency, individual investors named as lead plaintiffs | investor		5
Personal Injury Lawsuit [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency, number of lawsuits filed | lawsuit							1
Jawbone Patent Litigation [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency, patents allegedly infringed | patent			6		3
Loss contingency, additional patents allegedly infringed | patent				3
PurePulse Class Action Lawsuit [Member] | Pending Litigation [Member]
Loss Contingencies [Line Items]
Loss contingency, number of lawsuits filed | lawsuit						2
Loss contingency, number of researchers providing study for lawsuit | researcher	2

Stock Plan - Narrative (Details

Stock Plan - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	6 Months Ended
	May 31, 2015	Jul. 02, 2016	Jul. 01, 2016
Employee Stock Options And Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options		$ 232.9
Unrecognized compensation expense related to unvested options, estimated weighted average period		3 years 2 months 15 days
Common Class A [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of exercise price (in dollars per share)			$ 12.48
Common Class A [Member] | 2015 Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)		8,300,000
Common Class A [Member] | 2015 Employee Stock Purchase Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance (in shares)	3,750,000
Percent of share price available to employees	85.00%
Offering period	6 months

Stock Plan - Stock Option Activ

Stock Plan - Stock Option Activity (Details) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jul. 02, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of period (in shares) | shares	44,362
Granted (in shares) | shares	955
Exercised (in shares) | shares	(5,362)
Canceled (in shares) | shares	(1,578)
Balance, end of period (in shares) | shares	38,377
Options exercisable (in shares) | shares	20,516
Options vested and expected to vest (in shares) | shares	37,783
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Balance, weighted average exercise price, beginning of period (in dollars per share) | $ / shares	$ 3.20
Granted, weighted average exercise price (in dollars per share) | $ / shares	14.06
Exercised, weighted average exercise price (in dollars per share) | $ / shares	0.89
Canceled, weighted average exercise price (in dollars per share) | $ / shares	4.51
Balance, weighted average exercise price, end of period (in dollars per share) | $ / shares	3.74
Options exercisable, weighted average exercise price (in dollars per share) | $ / shares	2.09
Options vested and expected to vest, weighted average exercise price (in dollars per share) | $ / shares	$ 3.70
Options outstanding, aggregate intrinsic value, end of period | $	$ 343,154
Options exercisable, aggregate intrinsic value | $	215,055
Options vested and expected to vest, aggregate intrinsic value | $	$ 339,241

Stock Plan - Restricted Stock U

Stock Plan - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] shares in Thousands	6 Months Ended
	Jul. 02, 2016$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested balance—December 31, 2014 (in shares) | shares	3,292
Granted (in shares) | shares	6,967
Vested (in shares) | shares	(243)
Forfeited or canceled (in shares) | shares	(182)
Unvested balance—September 30, 2015 (in shares) | shares	9,834
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Unvested balance—December 31, 2014 (in dollars per share) | $ / shares	$ 34.27
Granted (in dollars per share) | $ / shares	14.28
Vested (in dollars per share) | $ / shares	21.05
Forfeited or canceled (in dollars per share) | $ / shares	19.80
Unvested balance—September 30, 2015 (in dollars per share) | $ / shares	$ 20.70

Stock Plan - Stock Compensation

Stock Plan - Stock Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 20,400	$ 7,747	$ 38,170	$ 12,650
Cost of revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	1,084	825	2,393	1,271
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	11,725	3,138	22,118	5,017
Sales and marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	2,927	1,322	5,462	2,629
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation	$ 4,664	$ 2,462	$ 8,197	$ 3,733

Income Taxes (Details)

Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Income Tax Disclosure [Abstract]
Income tax expense	$ 3,695	$ 17,048	$ 13,564	$ 45,442
Effective income tax rate	36.80%	49.10%	43.80%	40.90%
Unrecognized tax benefits	$ 28,500		$ 28,500

Net Income per Share Attribut53

Net Income per Share Attributable to Common Stockholders - Narrative (Details)	Jul. 02, 2016classvote
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Number of classes of stock | class	2
Common Class A [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock, votes per share	1
Common Class B [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Common stock, votes per share	10

Net Income per Share Attribut54

Net Income per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Earnings Per Share [Abstract]
Net income	$ 6,341	$ 17,681	$ 17,376	$ 65,678
Less: noncumulative dividends to preferred stockholders	0	(1,212)	0	(2,526)
Less: undistributed earnings to participating securities	0	(11,244)	0	(45,907)
Net income attributable to common stockholders—basic	6,341	5,225	17,376	17,245
Add: adjustments to undistributed earnings to participating securities	0	1,862	0	7,003
Net income attributable to common stockholders—diluted	$ 6,341	$ 7,087	$ 17,376	$ 24,248
Denominator:
Weighted-average shares of common stock—basic (in shares)	218,850	58,548	217,431	49,922
Effect of dilutive securities (in shares)	23,478	36,642	24,722	32,919
Weighted-average shares of common stock—diluted (in shares)	242,328	95,190	242,153	82,841
Net income per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.03	$ 0.09	$ 0.08	$ 0.35
Diluted (in dollars per share)	$ 0.03	$ 0.07	$ 0.07	$ 0.29

Net Income per Share Attribut55

Net Income per Share Attributable to Common Stockholders - Antidilutive Securities (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	8,117	127,828	7,432	135,505
Redeemable convertible preferred stock and stock options to purchase common stock [Member] | Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	3,861	0	3,548	799
Redeemable convertible preferred stock and stock options to purchase common stock [Member] | Preferred Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	126,020	0	132,898
Restricted Stock Units (RSUs) [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	4,256	0	3,884	0
Redeemable Convertible Preferred Stock Warrant [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount (in shares)	0	1,808	0	1,808

Significant Customer Informat56

Significant Customer Information and Other Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015	Dec. 31, 2015
Concentration Risk [Line Items]
Revenue	$ 586,528	$ 400,412	$ 1,091,884	$ 737,166
Geographic Concentration Risk [Member] | Non-US [Member]
Concentration Risk [Line Items]
Long-lived assets including property and equipment	$ 42,600		$ 42,600		$ 28,900
Revenue [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	16.00%	14.00%	17.00%	16.00%
Revenue [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	14.00%	12.00%	12.00%
Revenue [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	14.00%	13.00%	13.00%	12.00%
Revenue [Member] | Geographic Concentration Risk [Member]
Concentration Risk [Line Items]
Revenue	$ 586,528	$ 400,412	$ 1,091,884	$ 737,166
Revenue [Member] | Geographic Concentration Risk [Member] | United States [Member]
Concentration Risk [Line Items]
Revenue	445,192	312,666	796,877	577,975
Revenue [Member] | Geographic Concentration Risk [Member] | Americas excluding United States [Member]
Concentration Risk [Line Items]
Revenue	27,375	16,799	50,769	30,228
Revenue [Member] | Geographic Concentration Risk [Member] | Europe, Middle East, and Africa [Member]
Concentration Risk [Line Items]
Revenue	99,471	39,712	174,195	74,768
Revenue [Member] | Geographic Concentration Risk [Member] | APAC [Member]
Concentration Risk [Line Items]
Revenue	$ 14,490	$ 31,235	$ 70,043	$ 54,195
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			23.00%		15.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			18.00%		19.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Concentration Risk [Line Items]
Concentration risk, percentage			15.00%		23.00%

Acquisition - Narrative (Detail

Acquisition - Narrative (Details) - USD ($)	1 Months Ended			3 Months Ended		6 Months Ended
	May 31, 2016	Jun. 30, 2015	Mar. 31, 2015	Jul. 02, 2016	Jun. 30, 2015	Jul. 02, 2016	Jun. 30, 2015	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill				$ 25,217,000		$ 25,217,000		$ 22,157,000
Change in contingent consideration				$ 0	$ (7,704,000)	$ 0	$ (7,704,000)
Privately Held Company [Member]
Business Acquisition [Line Items]
Cash paid for acquisition	$ 7,000,000
Goodwill	3,100,000
Privately Held Company [Member] | In Process Research and Development [Member]
Business Acquisition [Line Items]
Intangibles acquired	$ 3,900,000
FitStar, Inc [Member]
Business Acquisition [Line Items]
Cash paid for acquisition			$ 11,500,000
Goodwill			22,157,000
Total consideration			32,500,000
Contingent consideration assumed in acquisition			7,700,000
Contingent consideration liability			7,700,000					$ 0
FitStar, Inc [Member] | Post Acquisition Compensation Expense [Member]
Business Acquisition [Line Items]
Business combination, contingent cash payments			$ 1,200,000
Requisite service period			3 years
FitStar, Inc [Member] | Other expense, net [Member]
Business Acquisition [Line Items]
Change in contingent consideration		$ 7,700,000
FitStar, Inc [Member] | General and administrative [Member] | Post Acquisition Compensation Expense [Member]
Business Acquisition [Line Items]
Transaction costs							$ 300,000
FitStar, Inc [Member] | Developed technology [Member]
Business Acquisition [Line Items]
Intangibles acquired			$ 12,640,000
Amortization period			7 years
FitStar, Inc [Member] | Customer relationships [Member]
Business Acquisition [Line Items]
Intangibles acquired			$ 128,000
Amortization period			1 year 3 months 18 days
FitStar, Inc [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Intangibles acquired			$ 1,150,000
Amortization period			5 years
FitStar, Inc [Member] | Common Stock [Member]
Business Acquisition [Line Items]
Shares issued, amount			$ 13,300,000
Shares issued (in shares)			1,059,688
FitStar, Inc [Member] | Common Stock [Member] | Post Acquisition Compensation Expense [Member]
Business Acquisition [Line Items]
Shares issued (in shares)			308,216
Shares repurchased, amount			$ 4,200,000

Acquisition - Assets Acquired a

Acquisition - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Jul. 02, 2016	Dec. 31, 2015	Mar. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 25,217	$ 22,157
FitStar, Inc [Member]
Business Acquisition [Line Items]
Goodwill			$ 22,157
Assumed liabilities, net of assets			(3,552)
Total			32,523
FitStar, Inc [Member] | Developed and core technology [Member]
Business Acquisition [Line Items]
Intangibles acquired			12,640
FitStar, Inc [Member] | Customer relationships [Member]
Business Acquisition [Line Items]
Intangibles acquired			128
FitStar, Inc [Member] | Trademarks [Member]
Business Acquisition [Line Items]
Intangibles acquired			$ 1,150