Fitbit 10-K 29 Feb 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2015	Feb. 19, 2016	Jun. 30, 2015
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-K
Document Period End Date	Dec. 31, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 3
Common Class A [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		137,971,036
Common Class B [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		78,035,345

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 535,846	$ 195,626
Marketable securities	128,632	0
Accounts receivable, net	469,260	238,859
Inventories	178,146	115,072
Prepaid expenses and other current assets	43,530	13,614
Total current assets	1,355,414	563,171
Property and equipment, net	44,501	26,435
Goodwill	22,157	0
Intangible assets, net	12,216	0
Deferred tax assets	83,020	42,001
Other assets	1,758	1,444
Total assets	1,519,066	633,051
Current liabilities:
Accounts payable	260,842	195,666
Accrued liabilities	194,977	70,940
Deferred revenue	44,448	9,009
Fitbit Force recall reserve	5,122	22,476
Income taxes payable	2,868	30,631
Long-term debt, current portion	0	132,589
Total current liabilities	508,257	461,311
Other liabilities	29,358	12,867
Redeemable convertible preferred stock warrant liability	0	15,797
Total liabilities	$ 537,615	$ 489,975
Commitments and contingencies (Note 8)
Redeemable convertible preferred stock, $0.0001 par value: no shares and 144,528,912 shares authorized as of December 31, 2015 and 2014, respectively; no shares and 139,851,483 shares issued and outstanding as of December 31, 2015 and 2014, respectively; aggregate liquidation preference of $0 as of December 31, 2015	$ 0	$ 67,814
Stockholders’ equity:
Common stock	0	4
Additional paid-in capital	737,820	7,979
Accumulated other comprehensive income	691	37
Retained earnings	242,919	67,242
Total stockholders’ equity	981,451	75,262
Total liabilities, redeemable convertible preferred stock and stockholders’ equity	1,519,066	633,051
Common Class A [Member]
Stockholders’ equity:
Common stock	10	0
Common Class B [Member]
Stockholders’ equity:
Common stock	$ 11	$ 0

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Redeemable convertible preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Redeemable convertible preferred stock authorized (in shares)	0	144,528,912
Redeemable convertible preferred stock issued (in shares)	0	139,851,483
Redeemable convertible preferred stock outstanding (in shares)	0	139,851,483
Redeemable Convertible preferred stock, liquidation preference	$ 0	$ 66,619,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	0	230,400,000
Common stock issued (in shares)	0	40,875,583
Common stock outstanding (in shares)	0	40,875,583
Common Class A [Member]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	600,000,000	0
Common stock issued (in shares)	99,416,351	0
Common stock outstanding (in shares)	99,416,351	0
Common Class B [Member]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	350,000,000	0
Common stock issued (in shares)	115,365,222	0
Common stock outstanding (in shares)	115,365,222	0

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Statement [Abstract]
Revenue	$ 1,857,998	$ 745,433	$ 271,087
Cost of revenue	956,935	387,776	210,836
Gross profit	901,063	357,657	60,251
Operating expenses:
Research and development	150,035	54,167	27,873
Sales and marketing	332,741	112,005	26,847
General and administrative	77,793	33,556	14,485
Change in contingent consideration	(7,704)	0	0
Total operating expenses	552,865	199,728	69,205
Operating income (loss)	348,198	157,929	(8,954)
Interest expense, net	(1,019)	(2,222)	(1,082)
Other expense, net	(59,230)	(15,934)	(3,649)
Income (loss) before income taxes	287,949	139,773	(13,685)
Income tax expense	112,272	7,996	37,937
Net income (loss)	175,677	131,777	(51,622)
Less: noncumulative dividends to preferred stockholders	(2,526)	(5,326)	0
Less: undistributed earnings to participating securities	(59,133)	(98,103)	0
Net income (loss) attributable to common stockholders—basic	114,018	28,348	(51,622)
Add: adjustments for undistributed earnings to participating securities	8,821	10,175	0
Net income (loss) attributable to common stockholders—diluted	$ 122,839	$ 38,523	$ (51,622)
Net income (loss) per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.88	$ 0.70	$ (1.32)
Diluted (in dollars per share)	$ 0.75	$ 0.63	$ (1.32)
Shares used to compute net income (loss) per share attributable to common stockholders:
Basic (in shares)	129,886	40,351	39,179
Diluted (in shares)	164,213	61,179	39,179

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Income (Loss) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 175,677	$ 131,777	$ (51,622)
Cash flow hedges:
Change in unrealized gain on cash flow hedges, net of tax expense of $1,509, $ —, and $ —, respectively	1,276	0	0
Less reclassification for realized net gains included in net income, net of tax expense of $759, $ —, and $ —, respectively	(525)	0	0
Net change, net of tax	751	0	0
Available-for-sale investments:
Change in unrealized loss on investments	(63)	0	0
Less reclassification for realized net gains included in net income	8	0	0
Net change, net of tax	(55)	0	0
Change in foreign currency translation adjustment, net of tax	(42)	37	0
Comprehensive income (loss)	$ 176,331	$ 131,814	$ (51,622)

Consolidated Statements of Com6

Consolidated Statements of Comprehensive Income (Loss) (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statement of Comprehensive Income [Abstract]
Change in unrealized gain on cash flow hedges, tax	$ 1,509	$ 0	$ 0
Reclassification for realized net gains included in net income, tax	$ 759	$ 0	$ 0

Consolidated Statements of Rede

Consolidated Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) Statement - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock [Member]	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings (Accumulated Deficit) [Member]
Beginning balance (in shares) at Dec. 31, 2012		110,354,028,000
Beginning balance at Dec. 31, 2012		$ 23,425
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants (unaudited) (in shares)		29,149,887,000
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants		$ 42,811
Ending balance (in shares) at Dec. 31, 2013		139,503,915,000
Ending balance at Dec. 31, 2013		$ 66,236
Beginning balance (in shares) at Dec. 31, 2012			36,856,749,000
Beginning balance at Dec. 31, 2012	$ (12,707)		$ 4	$ 202	$ 0	$ (12,913)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (unaudited) (in shares)			3,283,410,000
Issuance of common stock upon exercise of stock options	205			205
Stock-based compensation expense	620			620
Excess tax benefit from stock-based compensation	38			38
Net income (loss)	(51,622)					(51,622)
Ending balance (in shares) at Dec. 31, 2013			40,140,159,000
Ending balance at Dec. 31, 2013	$ (63,466)		$ 4	1,065	0	(64,535)
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants (unaudited) (in shares)		347,568,000
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants		$ 1,578
Ending balance (in shares) at Dec. 31, 2014	139,851,483	139,851,483,000
Ending balance at Dec. 31, 2014	$ 67,814	$ 67,814
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (unaudited) (in shares)			735,424,000
Issuance of common stock upon exercise of stock options	97			97
Stock-based compensation expense	6,804			6,804
Excess tax benefit from stock-based compensation	13			13
Net income (loss)	131,777					131,777
Other comprehensive income	37				37
Ending balance (in shares) at Dec. 31, 2014			40,875,583,000
Ending balance at Dec. 31, 2014	$ 75,262		$ 4	7,979	37	67,242
Increase (Decrease) in Temporary Equity [Roll Forward]
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants (unaudited) (in shares)		1,485,583,000
Issuance of redeemable convertible preferred stock upon exercise of redeemable convertible preferred stock warrants		$ 56,678
Conversion of redeemable convertible preferred stock to common stock upon public offering (unaudited) (in shares)		(141,337,066,000)
Conversion of redeemable convertible preferred stock to common stock upon initial public offering		$ (124,492)
Ending balance (in shares) at Dec. 31, 2015	0	0
Ending balance at Dec. 31, 2015	$ 0	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon public offering, net of offering costs			25,387,500,000
Issuance of common stock upon public offerings, net of offering costs	499,105		$ 3	499,102
Conversion of redeemable convertible preferred stock to common stock upon public offering (unaudited) (in shares)			141,337,066,000
Conversion of redeemable convertible preferred stock to common stock upon initial public offering	124,492		$ 14	124,478
Reclassification of redeemable convertible preferred stock warrant liability into additional paid in capital upon initial public offering	15,774			15,774
Issuance of common stock upon exercise of stock options (unaudited) (in shares)			5,396,591,000
Issuance of common stock upon exercise of stock options	4,018			4,018
Issuance of common stock in connection with acquisition (unaudited) (in shares)			1,059,688,000
Issuance of common stock in connection with acquisition	13,317			13,317
Issuance of common stock subject to vesting in connection with acquisition (unaudited) (in shares)			308,216,000
Issuance of common stock upon net exercise of common stock warrants (in shares)			416,929,000
Stock-based compensation expense	41,052			41,052
Excess tax benefit from stock-based compensation	32,100			32,100
Net income (loss)	175,677					175,677
Other comprehensive income	654				654
Ending balance (in shares) at Dec. 31, 2015			214,781,573,000
Ending balance at Dec. 31, 2015	$ 981,451		$ 21	$ 737,820	$ 691	$ 242,919

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Cash Flows from Operating Activities
Net income (loss)	$ 175,677	$ 131,777	$ (51,622)
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Provision for doubtful accounts	1,115	864	651
Provision for inventory obsolescence	5,060	2,964	1,099
Provision for inventory obsolescence related to Fitbit Force recall	0	0	10,251
Depreciation	19,405	6,131	3,012
Amortization of intangible assets	1,702	0	0
Write-off of property and equipment	1,206	1,004	1,712
Revaluation of redeemable convertible preferred stock warrant liability	56,655	13,272	3,370
Amortization of issuance costs and discount on debt	961	795	82
Stock-based compensation	41,024	6,804	620
Change in contingent consideration	(7,704)	0	0
Deferred income taxes	(42,538)	(42,001)	0
Excess of tax benefit from stock-based compensation	(32,100)	(13)	(38)
Other	(263)	0	0
Changes in operating assets and liabilities, net of acquisition:
Accounts receivable	(231,100)	(158,788)	(55,630)
Inventories	(68,108)	(61,595)	(47,376)
Prepaid expenses and other assets	(29,215)	(9,679)	(2,225)
Fitbit Force recall reserve	(17,354)	(60,462)	72,687
Accounts payable	56,759	123,761	50,881
Accrued liabilities and other liabilities	138,748	47,733	27,043
Deferred revenue	34,891	3,403	859
Income taxes payable	4,336	12,804	17,795
Net cash provided by operating activities	109,157	18,774	33,171
Cash Flows from Investing Activities
Change in restricted cash	0	2,310	(2,310)
Purchase of property and equipment	(30,566)	(26,495)	(7,524)
Purchase of marketable securities	(230,935)	0	0
Sales of marketable securities	58,011	0	0
Maturities of marketable securities	44,500	0	0
Acquisitions, net of cash acquired	(11,037)	0	0
Net cash used in investing activities	(170,027)	(24,185)	(9,834)
Cash Flows from Financing Activities
Proceeds from public offerings, net of underwriting discounts and commissions	505,275	0	0
Proceeds from issuance of debt and revolving credit facility	160,000	163,000	2,830
Repayment of debt	(294,503)	(41,346)	(596)
Payment of issuance costs	(748)	(2,575)	(45)
Payment of offering costs	(5,089)	0	0
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	0	0	42,811
Proceeds from exercise of stock options	4,018	97	205
Excess of tax benefit from stock-based compensation	32,100	13	38
Proceeds from exercise of redeemable convertible preferred stock warrants	0	75	0
Net cash provided by financing activities	401,053	119,264	45,243
Net increase in cash and cash equivalents	340,183	113,853	68,580
Effect of exchange rate on cash and cash equivalents	37	45	0
Cash and cash equivalents at beginning of period	195,626	81,728	13,148
Cash and cash equivalents at end of period	535,846	195,626	81,728
Supplemental Disclosure
Cash paid for interest	1,157	835	999
Cash paid for income taxes	150,923	34,616	12,930
Supplemental Disclosure of Non-Cash Investing and Financing Activity
Conversion of redeemable convertible preferred stock into Class B common stock	124,492	0	0
Reclassification of redeemable convertible preferred stock warrant liability to additional paid in capital	15,774	0	0
Issuance of redeemable convertible preferred stock upon net exercise of redeemable convertible preferred stock warrants	56,678	0	0
Purchase of property and equipment included in accounts payable	10,534	2,492	1,904
Issuance of redeemable convertible preferred stock warrants in connection with debt financing	0	0	170
Deferred offering costs included in accounts payable and accruals	1,080	0	0
Issuance of common stock in connection with acquisitions	13,317	0	0
Contingent consideration related to acquisitions	$ (7,704)	$ 0	$ 0

Business Overview

Business Overview	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Business Overview	Business Overview Fitbit, Inc. (the “Company”) is transforming the way millions of people around the world achieve their health and fitness goals. The Fitbit platform combines connected health and fitness devices with software and services, including an online dashboard and mobile apps, data analytics, motivational and social tools, personalized insights, and virtual coaching through customized fitness plans and interactive workouts. The Company sells devices through diversified sales channels that include distributors, retailers, a corporate wellness offering, and Fitbit.com. The Company was incorporated in Delaware in 2007. The Company has established wholly-owned subsidiaries globally and its corporate headquarters are located in San Francisco, California. In June 2015, the Company completed its initial public offering (“IPO”) of Class A common stock, in which the Company sold 22,387,500 shares and certain of its stockholders sold 19,673,750 shares, for which the Company did not receive any proceeds, including 5,486,250 shares pursuant to the underwriters’ option to purchase additional shares. The shares were sold at an initial public offering price of $20.00 per share for net proceeds of $420.9 million to the Company, after deducting underwriting discounts and commissions of $26.9 million . Offering costs incurred by the Company were approximately $5.0 million . In addition, in connection with the IPO: • The Company authorized two new classes of common stock— Class A common stock and 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. • All shares of the then-outstanding common stock, as well as options to purchase common stock and restricted stock units (“RSUs”), were reclassified into the right to receive an equivalent number of shares of Class B common stock. • All 139,851,483 shares of the then-outstanding redeemable convertible preferred stock were converted and reclassified into an equivalent number of shares of Class B common stock. This resulted in a reclassification of the redeemable convertible preferred stock balance of $67.8 million to additional paid-in capital. • The Company issued 274,992 shares of Series B redeemable convertible preferred stock and 1,210,591 shares of Series C redeemable convertible preferred stock upon the net exercise of redeemable convertible preferred stock warrants, which occurred immediately prior to the completion of its IPO. These shares were converted into and then sold as Class A common stock by the selling stockholders in the IPO. As a result, the Company revalued the warrants settled upon exercise as of the completion of the IPO and reclassified $ 56.7 million from the redeemable convertible preferred stock warrant liability balance to additional paid-in capital. In addition, all of the remaining outstanding redeemable convertible preferred stock warrants automatically converted to Class B common stock warrants upon the closing of the IPO. As a result, the Company revalued the warrants as of the completion of the IPO and reclassified the remaining redeemable convertible preferred stock warrant liability balance of $15.8 million to additional paid-in capital. • The Company recorded proceeds of $420.9 million to additional paid-in capital and reclassified $5.0 million of deferred offering costs previously recorded in other current assets as an offset to the proceeds from the IPO. In November 2015, the Company completed a follow-on offering of Class A common stock, in which the Company sold 3,000,000 shares and certain of its stockholders sold 16,550,000 shares, for which the Company did not receive any proceeds, including 2,550,000 shares pursuant to the underwriters’ option to purchase additional shares. The shares were sold at a public offering price of $29.00 per share for net proceeds of $84.4 million to the Company, after deducting underwriting discounts and commissions of $2.6 million . Offering costs incurred by the Company were approximately $1.2 million .

Basis of Presentation

Basis of Presentation	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation Principles of Consolidation The consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated. Stock Splits In June 2013, the Company effected a 4 -for-1 stock split of all outstanding shares of redeemable convertible preferred stock. In addition, in September 2014, the Company effected a 2 -for-1 stock split of all outstanding shares of the Company’s capital stock, including common stock and redeemable convertible preferred stock. In May 2015, the Company effected a 3 -for-2 stock split of all outstanding shares of the Company’s capital stock, including its common stock and its redeemable convertible preferred stock. All share, option, RSU, warrant, and per share information presented in the consolidated financial statements has been adjusted to reflect the stock splits on a retroactive basis for all periods presented and all share information is rounded down to the nearest whole share after reflecting the stock splits. Use of Estimates The preparation of consolidated financial statements in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the amounts reported and disclosed in the consolidated financial statements and accompanying notes. The estimates and assumptions made by management related to revenue recognition, accruals for the Fitbit Force recall, reserves for sales returns and incentives, reserves for warranty, valuation of stock options, fair value of warrant liability and derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, 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, 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 consolidated financial statements. Reclassifications In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes . This ASU requires that all deferred tax assets and liabilities, along with any related valuation allowance, be classified as noncurrent on the balance sheet. The Company early adopted this standard retrospectively in its fourth quarter of 2015 and reclassified all of its current deferred tax assets to noncurrent deferred tax assets on the consolidated balance sheets for all periods presented. Within the consolidated balance sheet as of December 31, 2014, the Company reclassified $33.6 million of current deferred tax assets and $8.4 million of other assets to noncurrent deferred tax assets. Comprehensive Income (Loss) Comprehensive income (loss) consists of two components, net income (loss) and other comprehensive income, net of tax. Other comprehensive income refers to revenue, expenses, and gains and losses that are recorded as an element of stockholders’ equity but are excluded from net income (loss). The Company’s other comprehensive income consists of net unrealized gains and losses on derivative instruments accounted for as cash flow hedges, foreign currency translation adjustments from those subsidiaries not using the U.S. dollar as their functional currency, and unrealized gains and losses on available-for-sale securities.

Significant Accounting Policies

Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Significant Accounting Policies	Significant Accounting Policies Cash, Cash Equivalents and Marketable Securities Cash and cash equivalents include all cash balances and highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents and marketable securities consist of money market funds, U.S. government and agency securities, commercial paper, and corporate notes and bonds. 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 in stockholders’ equity. Realized gains or losses and other-than-temporary impairments, if any, on available-for-sale securities are reported in other expense, net as incurred. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. Investments are reviewed periodically to identify possible other-than-temporary impairments. No impairment loss has been recorded on the securities 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. Fair Value of Financial Instruments Assets and liabilities recorded at fair value on a recurring basis are categorized based upon the level of judgment associated with inputs used to measure their fair values. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the reporting date. The Company estimates fair value by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —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 for substantially the full term of the assets or liabilities; and Level 3 —Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability. Foreign Currencies The Company and certain of the Company’s wholly-owned subsidiaries use the U.S. dollar as their functional currency. The Company’s subsidiaries that use the U.S. dollar as their functional currency remeasure local currency denominated monetary assets and liabilities at exchange rates in effect at the end of each period, and inventories, property, plant and equipment and other nonmonetary assets and liabilities at historical rates. Gains and losses from these remeasurements have been included in the Company’s operating results within other expense, net. Local currency transactions of these international operations are remeasured into U.S. dollars at the rates of exchange in effect at the date of the transaction. Foreign currency transaction losses were $ 2.6 million , $2.7 million , and $0.2 million for 2015, 2014, and 2013, respectively. The Company translates the assets and liabilities of its non-U.S. dollar functional currency subsidiaries into U.S. dollars using exchange rates in effect at the end of each period. Revenue and expenses for these subsidiaries are translated using rates that approximate those in effect during the related period. Gains and losses from translations are recognized in foreign currency translation included in accumulated other comprehensive income (loss). Derivative Instruments The Company accounts for its derivative instruments as either assets or liabilities and carries them at fair value. Derivatives held by the Company that are not designated as hedges are adjusted to fair value through earnings at each reporting date. In addition, the Company enters into derivatives that are accounted for as cash flow hedges. 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 in stockholders’ equity and subsequently reclassifies the gains or losses into revenue and operating expenses when the underlying hedged transactions are recognized. The Company periodically assesses the effectiveness of its cash flow hedges. The fair value of derivative assets and liabilities are included in prepaid expenses and other current assets and accrued liabilities on the consolidated balance sheets. Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, accounts receivables, and derivative instruments. Cash and cash equivalents are deposited with high quality financial institutions and may, at times, exceed federally insured limits. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal interest rate risk. The Company’s accounts receivable are derived from customers located principally in the United States. The Company maintains credit insurance for the majority of its customer balances, performs ongoing credit evaluations of its customers, and maintains allowances for potential credit losses on customers’ accounts when deemed necessary. Credit losses historically have not been significant. The Company continuously monitors customer payments and maintains an allowance for doubtful accounts based on its assessment of various factors including historical experience, age of the receivable balances, and other current economic conditions or other factors that may affect customers’ ability to pay. The Company’s derivative instruments expose it to credit risk to the extent that its counterparties may be unable to meet the terms of the agreements. The Company seeks to mitigate this risk by limiting counterparties to major financial institutions and by spreading the risk across several major financial institutions. In addition, the potential risk of loss with any one counterparty resulting from this type of credit risk is monitored on an ongoing basis. Supplier Concentration The Company relies on third parties for the supply and manufacture of its products, as well as third-party logistics providers. In instances where these parties fail to perform their obligations, the Company may be unable to find alternative suppliers or satisfactorily deliver its products to its customers on time, if at all. Inventories Inventories consist of finished goods and component parts, which are purchased from contract manufacturers and component suppliers. Inventories are stated at the lower of cost or market on a first-in, first-out basis. The Company assesses the valuation of inventory and periodically writes down the value for estimated excess and obsolete inventory based upon estimates of future demand and market conditions. Property and Equipment, Net Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets. Cost of maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. The useful lives of the property and equipment are as follows: Tooling and manufacturing equipment One to three years Furniture and office equipment Three years Purchased software Three years Capitalized internally-developed software Two to three years Leasehold improvements Shorter of remaining lease term or ten years Internally-Developed Software Costs The Company capitalizes eligible costs to acquire, develop, or modify internal-use software that are incurred subsequent to the preliminary project stage. Capitalized internally-developed software costs, net, were immaterial as of December 31, 2015 and 2014. Research and Development Research and development expenses consist primarily of personnel-related expenses, consulting and contractor expenses, tooling and prototype materials, and allocated overhead costs. Substantially all of the Company’s research and development expenses are related to developing new products and services and improving existing products and services. To date, research and development expenses have been expensed as incurred, because the period between achieving technological feasibility and the release of products and services for sale has been short and development costs qualifying for capitalization have been insignificant. Business Combinations, Goodwill, and Intangible Assets The Company allocates the fair value of purchase consideration to tangible assets, liabilities assumed, and intangible assets acquired based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is allocated to goodwill. The allocation of the purchase consideration requires management to make significant estimates and assumptions, especially with respect to intangible assets. These estimates can include, but are not limited to, future expected cash flows from acquired customers, acquired technology, and trade names from a market participant perspective, useful lives, and discount rates. Management’s estimates of fair value are based upon assumptions believed to be reasonable, but which are inherently uncertain and unpredictable and, as a result, actual results may differ from estimates. During the measurement period, which is up to one year from the acquisition date, the Company may record adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings. The Company assesses goodwill for impairment at least annually during the fourth quarter and whenever events or changes in circumstances indicate that the carrying value of the asset may not be recoverable. Consistent with the determination that the Company has one reporting segment, the Company has determined that there is one reporting unit and tests goodwill for impairment at the entity level. Goodwill is tested using the two-step process in accordance with ASC 350, Intangibles—Goodwill and Other . In the first step, the carrying amount of the reporting unit is compared to the fair value based on the fair value of the Company’s common stock. If the fair value of the reporting unit exceeds the carrying value, goodwill is not considered impaired and no further testing is required. If the carrying value of the reporting unit exceeds the fair value, goodwill is potentially impaired and the second step of the impairment test must be performed. In the second step, the implied fair value of the goodwill, as defined by ASC 350, is compared to its carrying amount to determine the amount of impairment loss, if any. Acquired finite-lived intangible assets are amortized over their estimated useful lives. The Company evaluates the recoverability of intangible assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review indicates that the carrying amount of property and equipment and intangible assets is not recoverable, the carrying amount of such assets is reduced to fair value. The Company has not recorded any such impairment charge during the years presented. Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the expected future undiscounted cash flows attributable to these assets. If it is determined that an asset is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the assets exceeds the expected discounted future cash flows arising from those assets. Redeemable Convertible Preferred Stock Warrant Liability The Company’s redeemable convertible preferred stock warrants require liability classification and accounting as the underlying preferred stock is considered redeemable as discussed in Note 9. At initial recognition, the warrants are recorded at their estimated fair value. The warrants are subject to remeasurement at each balance sheet date, with changes in fair value recognized as a component of other expense, net. In connection with the Company’s IPO, the Company remeasured the liability at the time of the IPO and then reclassified the redeemable convertible preferred stock warrant liability to additional paid-in capital as these warrants converted to Class B common stock warrants. See Note 9 for additional information. As of December 31, 2015, there were no longer any redeemable convertible preferred stock warrants or any Class B common stock warrants outstanding. Revenue Recognition The Company derives substantially all of its revenue from sales of connected health and fitness devices and accessories. The Company also generates a small portion of revenue from its subscription-based services. The Company recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred, the sales price is fixed or determinable, and collection is reasonably assured. The Company considers delivery of its products to have occurred once title and risk of loss has been transferred. For customers where transfer of risk of loss is at the customer’s destination, the Company uses estimates to defer sales at the end of the reporting period based on historical experience of average transit time. The Company recognizes revenue, net of estimated sales returns, sales incentives, discounts, and sales tax. The Company generally recognizes revenue for products sold through retailers and distributors on a sell-in basis. The Company enters into multiple element arrangements that include hardware, software, and services. The first deliverable is the hardware and firmware essential to the functionality of the connected health and fitness device delivered at the time of sale. The second deliverable is the software services included with the products, which are provided free of charge and enable users to sync, view, and access real-time data on the Company’s online dashboard and mobile apps. The third deliverable is the embedded right included with the purchase of the device to receive, on a when-and-if-available basis, future unspecified firmware upgrades and features relating to the product’s essential firmware. Commencing in the first quarter of 2015, the Company began accounting for the embedded right as a separate unit of accounting, which is when it believes, through public announcements, it had created an implied obligation to, from time to time, provide future unspecified firmware upgrades and features to the firmware to improve and add new functionality to the health and fitness devices. In addition, the Company occasionally offers a fourth deliverable in bundled arrangements that allows access to subscription-based services related to the Company’s FitStar offering. The Company allocates revenue to all deliverables based on their relative selling prices. The Company uses a hierarchy to determine the selling price to be used for allocating revenue to deliverables: (i) vendor-specific objective evidence (“VSOE”) of fair value, (ii) third-party evidence (“TPE”), and (iii) best estimate of the selling price (“BESP”). The Company’s process for determining its BESP considers multiple factors including consumer behaviors and the Company’s internal pricing model and may vary depending upon the facts and circumstances related to each deliverable. BESP for the health and fitness devices and unspecified upgrade rights reflect the Company’s best estimate of the selling prices if they were sold regularly on a stand-alone basis and comprises the majority of the arrangement consideration. BESP for upgrade rights currently ranges from $1 to $3 . TPE for the online dashboard and mobile apps is currently estimated at $0.99 . VSOE for access to FitStar subscription-based services is based on the price charged when sold separately. Amounts allocated to the connected health and fitness devices are recognized at the time of delivery, provided the other conditions for revenue recognition have been met. Amounts allocated to the online dashboard and mobile apps and unspecified upgrade rights are deferred and recognized on a straight-line basis over their estimated usage period of approximately eight to thirteen months. The Company offers its users the ability to purchase subscription-based services, through which the users receive incremental features, including access to a digital personal trainer, in-depth analytics regarding the user’s personal metrics, or video-based customized workouts. Amounts paid for subscriptions are deferred and recognized ratably over the service period which is typically one year. Revenue from subscription-based services was less than 1% of revenue for all periods presented. In addition, the Company offers access to software and services to certain customers in the corporate wellness program, which includes distribution capabilities, a real-time dashboard, and support services. The Company is currently unable to establish VSOE or TPE for the corporate wellness software and services. BESP for the corporate wellness software and services is determined based on the Company’s internal pricing model for anticipated renewals for existing customers and pricing for new customers. Revenue allocated to the corporate wellness software and services is deferred and recognized on a straight-line basis over the estimated access period of one year, which is the typical service period. Revenue for corporate wellness software and services was less than 1% of revenue for all periods presented. The Company accounts for shipping and handling fees billed to customers as revenue. Sales taxes and value added taxes (“VAT”) collected from customers are remitted to governmental authorities are not included in revenue, and are reflected as a liability on the consolidated balance sheets. Rights of Return, Stock Rotation Rights, and Price Protection The Company offers limited rights of return, stock rotation rights, and price protection under various policies and programs with its retailer and distributor customers and end-users. Below is a summary of the general provisions of such policies and programs: • Certain retailers and distributors are allowed to return products that were originally sold through to an end user, called “open box” returns, and such returns may be made at any time after original sale. • All purchases through Fitbit.com are covered by a 45 -day right of return. • Distributors are allowed stock rotation rights which are limited rights of return of products purchased during a prior period, generally one quarter. • Distributors and retailers are allowed return rights for defective products. • Certain distributors are offered price protection that allows for the right to a partial credit for unsold inventory held by the distributor if the Company reduces the selling price of a product. The Company meets all conditions required to recognize revenue at the time of sale when a right of return exists. For example, the price to the buyer is fixed or determinable at time of sale; the buyer’s obligation to pay is not contingent on resale of the product; and the Company is able to reasonably estimate the amount of future returns. The Company estimates and records reserves for these policies and programs as a reduction of revenue and accounts receivable. On a quarterly basis, the amount of revenue that is reserved for future returns is calculated based on the Company’s historical trends and data specific to each reporting period. The Company reviews the actual returns evidenced in prior quarters as a percent of related revenue to determine the historical returns rate. It then applies the historical returns rate to the current period revenue as a basis for estimating future returns. Through December 31, 2015 , actual returns have primarily been open-box returns. In addition, through December 31, 2015 , the Company has had minimal stock rotation or price protection claims. When necessary, the Company also provides a specific reserve for product in the distribution channel in excess of estimated requirements. This estimate can be affected by the amount of a particular product in the channel, the rate of sell-through, product plans, and other factors. The Company also considers whether there are circumstances which may result in anticipated returns higher than the historical return rate from direct users and records an additional reserve as necessary. Sales Incentives The Company offers sales incentives through various programs, consisting primarily of cooperative advertising and marketing development fund programs. The Company records advertising and marketing development fund programs with customers as a reduction to revenue unless it receives an identifiable benefit in exchange for credits claimed by the customer and can reasonably estimate the fair value of the identifiable benefit received, in which case the Company records it as a marketing expense. The Company recognizes a liability and reduces revenue for rebates or other incentives based on the estimated amount of rebates or credits that will be claimed by customers. Cost of Revenue Cost of revenue consists of product costs, including costs of contract manufacturers for production, shipping and handling costs, packaging, warranty replacement costs, fulfillment costs, manufacturing and tooling equipment depreciation, warehousing costs, excess and obsolete inventory write-downs, costs related to the Fitbit Force product recall, and certain allocated costs related to management, facilities, and personnel-related expenses and other expenses associated with supply chain logistics. Advertising Costs and Point of Purchase (“POP”) Displays Costs related to advertising and promotions, excluding co-op advertising costs, are expensed to sales and marketing as incurred. Advertising and promotion expenses, including expenses for POP displays, for 2015, 2014, and 2013 were $237.0 million , $71.9 million , and $9.5 million , respectively. Co-op advertising costs are recorded as a reduction to revenue, and for 2015, 2014, and 2013 were $38.3 million , $12.7 million , and $5.7 million , respectively. The Company provides retailers with POP displays, generally free of charge, in order to facilitate the marketing of the Company’s products within retail stores. Any amounts capitalized related to the costs of the POP displays are recorded as prepaid expense on the consolidated balance sheets and recognized as expense over the expected period of the benefit provided by these assets, which is generally 12 months. The related expenses are included in sales and marketing expenses on the consolidated statements of operations. Product Warranty The Company offers a standard product warranty that the product will operate under normal use for a period of one year from date of original purchase except in the European Union where the Company provides a two -year warranty. The Company has the obligation, at its option, to either repair or replace the defective product. At the time revenue is recognized, an estimate of future warranty costs is recorded as a component of cost of revenues. Factors that affect the warranty obligation include product failure rates, service delivery costs incurred in correcting the product failures, and warranty policies. The warranty obligation does not consider historical experience of the Fitbit Force product as a separate reserve has been established for the Fitbit Force recall. The Company’s products are manufactured by third-party contract manufacturers, and in certain cases, the Company may have recourse to such third-party contract manufacturers. Fitbit Force Product Recall The Company established reserves for the Fitbit Force recall when circumstances giving rise to the recall became known. It considered various factors in estimating the product recall exposure. These include estimates for: • refunds and product returns from retailer and distributor customers and end-users, which were charged to revenue and cost of revenue on the consolidated statements of operations; • 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 by the Company’s contract manufacturers, write-offs of tooling and manufacturing equipment, which were charged to cost of revenue on the consolidated statements of operations; and • legal fees and settlement costs, which were charged to general and administrative expenses on the consolidated statements of operations. These factors above are updated and reevaluated each period and the related reserves are adjusted when factors indicate that the recall reserves are either insufficient to cover or exceed the estimated product recall expenses. Stock-Based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date using the Black-Scholes option-pricing model. The fair value of restricted stock units (“RSUs”) is the fair value of the Company’s common stock on the grant date. Stock-based compensation expense is recognized over the requisite service period on a straight-line basis and is recorded net of estimated forfeitures. Stock-based compensation expenses for options granted to non-employees as consideration for services received are measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, using the Black-Scholes option-pricing model, whichever can be more reliably measured. Stock-based compensation expenses for options granted to non-employees are remeasured as the underlying options vest. The Company recognizes tax benefits related to stock-based compensation to the extent that the total reduction to its income tax liability from stock-based compensation is greater than the amount of the deferred tax assets previously recorded in anticipation of these benefits. The Company recognizes a benefit from stock-based compensation in equity to the extent that an incremental tax benefit is realized by following the ordering provisions of the tax laws. Segment Information The Company operates as one operating segment as it only reports financial information on an aggregate and consolidated basis to its Chief Executive Officer, who is the Company’s chief operating decision maker. Income Taxes The Company utilizes the asset and liability method of accounting for income taxes, which requires the recognition of deferred tax assets and liabilities for expected future consequences of temporary differences between the financial reporting and income tax bases of assets and liabilities using enacted tax rates. The Company makes estimates, assumptions, and judgments to determine its expense for income taxes and also for deferred tax assets and liabilities and any valuation allowances recorded against its deferred tax assets. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes that recovery is not likely, the Company establishes a valuation allowance. The calculation of the Company’s income tax expense involves the use of estimates, assumptions, and judgments while taking into account current tax laws, its interpretation of current tax laws, and possible outcomes of future tax audits. The Company has established reserves to address potential exposures related to tax positions that could be challenged by tax authorities. Although the Company believes its estimates, assumptions, and judgments to be reasonable, any changes in tax law or its interpretation of tax laws and the resolutions of potential tax audits could significantly impact the amounts provided for income taxes in its consolidated financial statements. The calculation of the Company’s deferred tax asset balance involves the use of estimates, assumptions, and judgments while taking into account estimates of the amounts and type of future taxable income. Actual future operating results and the underlying amount and type of income could differ materially from the Company’s estimates, assumptions, and judgments, thereby impacting its financial position and operating results. The Company includes interest and penalties related to unrecognized tax benefits within income tax expense. Interest and penalties related to unrecognized tax benefits have been recognized in the appropriate periods presented. Net Income (Loss) 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. The Company considers its redeemable convertible preferred stock to be participating securities. The holders of the redeemable convertible preferred stock did not have a contractual obligation to share in losses. 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. 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. 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 common stock 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. In 2013 , basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period without consideration of common stock equivalents or the participation rights of the preferred stock as they do not share in losses. As the Company was in a net loss position in 2013, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive. Recent Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09 (ASC 606), Revenue from Contracts with Customers , which affects any entity that either enters into contracts with custo

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Fair Value Measurements	Fair Value Measurements The carrying values of the Company’s accounts receivable and accounts payable, approximated their fair values due to the short period of time to maturity or repayment. The carrying value of the Company’s long-term debt approximates its fair value as of December 31, 2014 , as the debt carries a variable rate or market rates currently available to the Company and other assumptions have not changed significantly. 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): December 31, 2015 Level 1 Level 2 Level 3 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 December 31, 2014 Level 1 Level 2 Level 3 Total Assets: Derivative assets $ — $ 316 $ — $ 316 Liabilities: Redeemable convertible preferred stock warrant liability $ — $ — $ 15,797 $ 15,797 Derivative liabilities — 105 — 105 Total $ — $ 105 $ 15,797 $ 15,902 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 are comprised of derivative financial instruments associated with hedging activity is further discussed in Note 5. 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 and forward 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. The Company’s Level 3 liabilities measured and recorded on a recurring basis consist of the redeemable convertible preferred stock warrant liability and contingent consideration. The fair value of the warrant liability is calculated using an option-pricing model as discussed in Note 9. Generally, increases or decreases in the fair value of the underlying redeemable convertible preferred stock would result in a directionally similar impact in the fair value measurement of the associated warrant liability. The unexercised warrants to purchase redeemable convertible preferred stock were converted into warrants to purchase shares of Class B common stock upon the closing of the IPO. As a result, the Company revalued and reclassified the redeemable convertible preferred stock liability to additional paid-in capital upon the closing of the IPO. The following table sets forth a summary of the changes in the fair value of the redeemable convertible preferred stock warrant liability (in thousands): Balance at December 31, 2012 $ 488 Fair value of redeemable convertible preferred stock warrants issued 170 Change in fair value 3,370 Balance at December 31, 2013 4,028 Settlement of warrant liability upon exercise (1,503 ) Change in fair value 13,272 Balance at December 31, 2014 15,797 Change in fair value 56,655 Settlement of warrant liability upon exercise (56,678 ) Reclassification of unexercised warrants to additional paid in capital upon the IPO (15,774 ) Balance at December 31, 2015 $ — The Company’s acquisition-related contingent consideration is determined using the Monte Carlo simulation method. The increases or decreases in the fair value of the contingent consideration payable could result from changes in the anticipated fair value of the Company’s common stock, stock price volatility, and probability of various market-based scenarios. As the fair value measure is based on significant inputs that are not observable in the market, they are categorized as Level 3. For additional information on the contingent consideration, see Note 15. The following table sets forth a summary of the changes in the fair value of the acquisition-related contingent consideration (in thousands): Balance at December 31, 2014 $ — Addition from acquisition 7,704 Change in fair value of contingent consideration (7,704 ) Balance at December 31, 2015 $ — There have been no transfers between fair value measurement levels during 2014 and 2015 .

Financial Instruments

Financial Instruments	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Financial Instruments	Financial Instruments Cash, Cash Equivalents, and Marketable Securities The following table sets forth the 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 As of December 31, 2014, the Company did not carry any investments in marketable securities. All available-for-sale investments as of December 31, 2015 have a contractual maturity of one year or less. The following table presents fair values and gross unrealized losses of investments that have been in an unrealized loss position for less than twelve months as of December 31, 2015 (in thousands): Fair Value Gross Unrealized Losses U.S. government agencies $ 113,314 $ (4 ) Corporate debt securities 193,964 (55 ) Total $ 307,278 $ (59 ) There were no available-for-sale investments as of December 31, 2015 that have been in a continuous unrealized loss position for greater than twelve months. 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 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 expense, net. If the hedged transaction becomes probable of not occurring, the corresponding amounts in accumulated other comprehensive income would immediately be reclassified as ineffectiveness to other 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 $346.6 million and $34.9 million in cash flow hedges for forecasted revenue and expense transactions, respectively, as of December 31, 2015. Balance Sheet Hedges The Company enters into foreign exchange contracts to hedge 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 expense, net and offset the foreign currency gain or loss on the underlying net monetary assets or liabilities. The notional amount of foreign currency contracts open in U.S. dollar equivalents was $47.2 million and $37.2 million as of December 31, 2015 and 2014, 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 consolidated balance sheets. The following table presents the fair value of the Company’s foreign currency derivative contracts as of the dates presented (in thousands): December 31, 2015 December 31, 2014 Balance Sheet Location Fair Value Derivative Assets Fair Value Derivative Liabilities Fair Value Derivative Assets Fair Value Derivative Liabilities Cash flow designated hedges Prepaid expense and other current assets $ 3,116 $ — $ — $ — Cash flow designated hedges Accrued liabilities — 1,327 — — Hedges not designated Prepaid expense and other current assets 2,886 — 316 — Hedges not designated Accrued liabilities — 1,313 — 105 Total fair value of derivative instruments $ 6,002 $ 2,640 $ 316 $ 105 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 (“OCI”) and the consolidated statement of operations for the periods presented (in thousands): Year Ended December 31, Income Statement Location 2015 2014 Foreign exchange cash flow hedges: Gain (loss) recognized in OCI—effective portion $ 2,785 $ — Gain (loss) reclassified from OCI into income—effective portion Revenue 2,183 — Gain (loss) reclassified from OCI into income—effective portion Operating expenses (899 ) — Gain (loss) recognized in income—ineffective portion Other expense, net 202 — Foreign exchange balance sheet hedges: Gain (loss) recognized in income Other expense, net $ 5,861 $ 211 As of December 31, 2015, 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 consolidated balance sheets. In July 2015, the Company started to enter 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 table sets forth the available offsetting of net derivative assets under the master netting arrangements as of December 31, 2015 (in thousands): Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Gross Amounts Not Offset 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 table sets forth the available offsetting of net derivative liabilities under the master netting arrangements as of December 31, 2015 (in thousands): Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Gross Amounts Not Offset 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	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Accounts Receivable Reserves Changes in accounts receivable reserves were as follows (in thousands): Allowance for Doubtful Accounts Revenue Reserve Balance at December 31, 2012 $ 92 $ 3,187 Increases 651 20,307 Write-offs/returns taken — (8,078 ) Balance at December 31, 2013 743 15,416 Increases 864 42,740 Write-offs/returns taken (769 ) (31,597 ) Balance at December 31, 2014 838 26,559 Increases 1,115 169,677 Write-offs/returns taken (128 ) (122,191 ) Balance at December 31, 2015 $ 1,825 $ 74,045 Inventories Inventories consisted of the following (in thousands): December 31, 2015 2014 Components $ 5,359 $ 53,383 Finished goods 172,787 61,689 Total inventories $ 178,146 $ 115,072 Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2015 2014 Prepaid income taxes $ 11,889 $ — POP displays, net 9,990 7,121 Derivative assets 6,002 316 Prepaid expenses and other current assets 15,649 6,177 Total prepaid expenses and other current assets $ 43,530 $ 13,614 Property and Equipment, Net Property and equipment, net, consisted of the following (in thousands): December 31, 2015 2014 Tooling and manufacturing equipment $ 53,092 $ 28,344 Furniture and office equipment 6,809 2,891 Purchased and internally-developed software 3,794 1,396 Leasehold improvements 8,388 3,594 Total property and equipment 72,083 36,225 Less: Accumulated depreciation and amortization (27,582 ) (9,790 ) Property and equipment, net $ 44,501 $ 26,435 Goodwill and Intangible Assets The changes in the carrying amount of goodwill for 2015 were as follows (in thousands). See Note 15 for additional information. Goodwill Balance at December 31, 2014 $ — Goodwill acquired 22,562 Subsequent goodwill adjustments (405 ) Balance at December 31, 2015 $ 22,157 There were no recognized intangible assets outstanding as of December 31, 2014. The carrying amounts of the intangible assets as of December 31, 2015 were as follows (in thousands, except useful life). See Note 15 for additional information. December 31, 2015 Weighted Average Remaining Useful Life (years) Gross Accumulated Amortization Net Developed technology $ 12,640 $ (1,442 ) $ 11,198 6.3 Trademarks and other 1,278 (260 ) 1,018 4.1 Total intangible assets, net $ 13,918 $ (1,702 ) $ 12,216 Total amortization expense related to intangible assets was $1.7 million for 2015, respectively. The estimated future amortization expense of acquired intangible assets to be charged to cost of revenue and operating expenses after 2015, is as follows (in thousands): Cost of Revenue Operating Expenses Total 2016 $ 1,806 $ 281 $ 2,087 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 intangible assets, net $ 11,198 $ 1,018 $ 12,216 Accrued Liabilities Accrued liabilities consisted of the following (in thousands): December 31, 2015 2014 Product warranty $ 40,212 $ 20,098 Accrued sales and marketing 33,389 154 Accrued co-op advertising and marketing development funds 29,077 7,679 Employee related liabilities 27,394 4,115 Accrued sales incentives 24,324 3,426 Accrued manufacturing expense and freight 10,723 16,229 Sales taxes and VAT payable 8,349 2,291 Inventory received but not billed 4,292 6,242 Accrued legal fees 3,138 678 Derivative liabilities 2,640 105 Customer deposits 2,062 6,391 Other 9,377 3,532 Accrued liabilities $ 194,977 $ 70,940 Product warranty reserve activities were as follows (in thousands): Reserve For Product Warranty (1) Balance at December 31, 2012 $ 2,232 Charged to cost of revenue 9,078 Settlement of claims (2,830 ) Balance at December 31, 2013 8,480 Charged to cost of revenue 19,462 Settlement of claims (7,844 ) Balance at December 31, 2014 20,098 Charged to cost of revenue 55,642 Changes in estimate related to pre-existing warranties (8,968 ) Settlement of claims (26,560 ) Balance at December 31, 2015 $ 40,212 (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. The changes in estimate related to pre-existing warranties resulted from a reduction in the estimated number of units to be replaced and in the estimated cost of replacement units based on additional historical experience. Fitbit Force Recall Reserve In March 2014, the Company announced a recall for one of its products, the Fitbit Force (“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): Reserve For Fitbit Force Recall Balance at December 31, 2012 $ — Charged to revenue 30,607 Charged to cost of revenue 49,493 Charged to general and administrative 2,838 Settlement of claims — Balance at December 31, 2013 82,938 Charged to revenue 8,112 Charged to cost of revenue 11,339 Charged to general and administrative 505 Settlement of claims (80,418 ) Balance at December 31, 2014 22,476 Benefit to cost of revenue (5,755 ) Benefit to general and administrative (1,174 ) Settlement of claims (10,425 ) Balance at December 31, 2015 $ 5,122 During 2013, the Company recorded excess and obsolete Fitbit Force inventory-related amounts of $10.3 million , included in the reserve, and wrote-off $1.7 million for specialized Fitbit Force tooling and manufacturing equipment to cost of revenue as incurred in the consolidated statement of operations. During 2014, legal fees of $2.9 million were recognized as incurred, in addition to legal settlement costs of $0.5 million related to the Fitbit Force recall, which were included in general and administrative costs in the consolidated statement of operations. During 2015, a benefit to cost of revenue of $5.8 million was recognized due to a change in estimate of costs to fulfill Fitbit Force returns. In addition, a benefit to legal expenses of $4.4 million was recognized in general and administrative costs, of which $1.2 million was previously included in the Fitbit Force recall reserve, due to the settlement of Fitbit Force legal liabilities. See Note 8. for additional information on the legal settlement. Accumulated Other Comprehensive Income The components and activity of accumulated other comprehensive income (“AOCI”), net of tax, were as follows (in thousands): Unrealized Gains on Cash Flow Hedges Currency Translation Adjustments Unrealized Gains (Losses) on Available-for-Sale Investments Total Balance at December 31, 2014 $ — $ 37 $ — $ 37 Other comprehensive income (loss) before reclassifications 1,276 (42 ) (63 ) 1,171 Amounts reclassified from AOCI (525 ) — 8 (517 ) Other comprehensive income (loss) 751 (42 ) (55 ) 654 Balance at December 31, 2015 $ 751 $ (5 ) $ (55 ) $ 691 Other comprehensive income consisted only of currency translation adjustments of an immaterial amount in 2014, and there was no other comprehensive income in 2013.

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2015
Debt Disclosure [Abstract]
Long-Term Debt	Long-Term Debt 2012 Financing Facility In August 2012, the Company entered into a debt agreement with Silicon Valley Bank (“SVB”) with a borrowing capacity of $26.0 million consisting of a $14.0 million revolving line of credit, a $3.0 million senior term loan, and a $9.0 million mezzanine term loan facility. The revolving line of credit, senior term loan, and mezzanine term loan facility were all terminated in August 2014. 2014 Credit Agreement In August 2014, the Company entered into an amended and restated credit agreement (“Asset-Based Credit Facility”) with SVB, as administrative agent and lender, and several other lenders, including affiliates of Morgan Stanley & Co. LLC, SunTrust Robinson Humphrey, Inc., and Deutsche Bank Securities Inc . 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. The borrowing base is determined by the Company’s collateral agents based on several variables, including percentages of the book value of certain eligible accounts receivable and a percentage of certain eligible inventories. Borrowings under the Asset-Based Credit Facility could be drawn as Alternate Base Rate or ABR loans or Eurodollar loans. ABR loans bore 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 bore interest at a variable rate based on the LIBOR rate and Euro currency reserve requirements. The Company was also required to pay an annual commitment fee on the average daily unused portion of the facility of 0.25% , 0.35% , or 0.45% , based on usage of the facility. As of December 31, 2014, the effective interest rate on the revolving line of credit was 4.25 % The Asset-Based Credit Facility required the Company to comply with certain financial covenants, including maintaining a consolidated fixed charge coverage ratio of at least 1. 1 :1, consolidated leverage ratios of between 3 :1 and 2 :1, and levels of liquidity of not less than $15.0 million . The Asset-Based Credit Facility also required the Company to comply with certain non-financial covenants. The Company was in compliance with these covenants as of December 31, 2014. As of December 31, 2014, the Company had $125.0 million of outstanding borrowings under the Asset-Based Credit Facility. In January 2015, the Company repaid $125.0 million of its indebtedness under the Asset-Based Credit Facility. 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 (“Cash Flow Facility”) with an affiliate of Morgan Stanley & Co. LLC, as administrative agent and collateral agent, and several other lenders, including SVB and an affiliate of SunTrust Robinson Humphrey, Inc. In October 2014, the Company entered into an incremental joinder agreement with an affiliate of Barclays Capital, Inc., which 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. Borrowings under the Cash Flow Facility could be drawn as ABR loans or Eurodollar loans. ABR loans under our Cash Flow Facility bore interest at a variable rate equal to the applicable margin plus the highest of (i) 3.5% , (ii) the prime rate, (iii) the federal funds effective rate plus 0.5% , and (iv) the adjusted LIBOR rate plus 1.0% . Eurodollar loans under the Cash Flow Facility bore interest at a variable rate for any day based on the LIBOR rate and Euro currency reserve requirements. The Company was also required to pay an annual commitment fee on the average daily unused portion of the facility of 0.375% or 0.5% , based on usage of the facility. As of December 31, 2014, the effective interest rate on the revolving line of credit was 3.59% . The Cash Flow Facility also required the Company to comply with certain financial covenants, including maintaining certain consolidated leverage ratios of between 3 :1 and 2 :1, and other non-financial covenants. As of December 31, 2014, the Company had $8.0 million of outstanding borrowings under the Cash Flow Facility. In March 2015, the Company repaid $8.0 million of its indebtedness under the Cash Flow Facility. 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, with Silicon Valley Bank, or SVB, as administrative agent, collateral agent, and lender, SunTrust Bank as syndication agent, SunTrust Robinson Humphrey, Inc. and several other lenders 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 our 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. Subsequent to December 31, 2015, the Company requested and received a waiver from the lender group to extend the deadline for compliance of a non-financial covenant to March 1, 2016. The Company expects to remain in compliance with the debt covenants, however, no assurances can be provided that the Company will continue to remain in compliance with the debt covenants. Obligations under the credit facility are secured by substantially all of our assets, excluding our intellectual property. As of December 31, 2015, there were no outstanding borrowings under the Senior Facility. The fair value of warrants issued in connection with debt agreements prior to 2012 was recorded as a debt discount and is amortized to interest expense using the straight-line method which approximated the effective interest method over the term of the related debt agreement. In addition, capitalized issuance costs are amortized to interest expense over the term of the related financing arrangement on a straight-line basis. Interest expense for 2015, 2014, and 2013 was $1.0 million , $2.2 million , and $1.1 million , respectively. Letters of Credit As of December 31, 2015 and 2014, the Company had outstanding letters of credit of $17.1 million and $2.9 million , respectively, issued to cover the security deposit on the lease of its office headquarters in San Francisco, California, and other facility leases.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company’s principal facility is located in San Francisco, California. The Company also 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. All of Company’s leases are accounted for as operating leases. Rent expense is recorded over the lease terms on a straight-line basis. Rent expense was $8.4 million , $4.1 million , and $0.9 million for 2015, 2014, and 2013, respectively. Future minimum payments under the leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Amounts 2016 $ 16,843 2017 20,825 2018 19,835 2019 18,789 2020 15,312 Thereafter 52,020 Total $ 143,624 Purchase Commitments The aggregate amount of purchase orders open as of December 31, 2015 was approximately $452.4 million . The Company cannot determine the aggregate amount of such purchase orders that represent contractual obligations because purchase orders may represent authorizations to purchase rather than binding agreements. The Company’s purchase orders are based on its current needs and are fulfilled by its suppliers, contract manufacturers, and logistics providers within short periods of time. 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 remain outstanding, including several complaints filed in 2015. 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 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. These personal injury complaints remain outstanding. 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 proceeds received. Jawbone. On May 27, 2015, 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 our 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 us (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 Fitbit 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 is currently scheduled for March 22, 2016. On June 10, 2015, Jawbone and 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 our 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 the action brought against us 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 the Company and certain of its 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 Fitbit 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, and has now set a hearing on May 9-16, 2016 and a target date for completion of the investigation on 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 U.S. District Court for the District of Delaware, asserting that Jawbone’s 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 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. 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. Because the Company is in the early stages of these litigation matters, the Company is unable to estimate a reasonably possible 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. A hearing on the motion to dismiss is currently scheduled for March 16, 2016. The Company believes that the plaintiffs’ allegations are without merit, and intend 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 range of loss, if any, that may result from this matter. Heart Rate Monitoring . 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 monitoring 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. The Company believes that the plaintiffs’ allegations are without merit, and intend 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 range of loss, if any, that may result from this matter. Federal Securities Class Action . On January 11, 2016, a putative class action lawsuit alleging violations of federal securities laws 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 lawsuit alleges violations of the Securities Act of 1933 and the Securities Exchange Act of 1934 by the Company and the officers for allegedly making materially false and misleading statements regarding its business and operations between June 18, 2015 and November 13, 2015. Plaintiff seeks 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 January 6, 2016; and/or (ii) pursuant to 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. The Company believes that the plaintiff’s allegations are without merit, and intend 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 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 range of loss. 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 parties 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.

Redeemable Convertible Preferre

Redeemable Convertible Preferred Stock and Warrants	12 Months Ended
	Dec. 31, 2015
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock and Warrants	Redeemable Convertible Preferred Stock and Warrants Redeemable Convertible Preferred Stock In connection with the closing of the Company’s IPO, all shares of the Company’s then-outstanding redeemable convertible preferred stock automatically converted on a one -for-one basis into an aggregate of 139,851,483 shares of Class B common stock. Redeemable convertible preferred stock outstanding as of December 31, 2014 and immediately prior to the conversion into Class B common stock and December 31, 2014 consisted of the following (in thousands, except per share data): Shares Authorized Shares Outstanding Price per Share Net Carrying Value Liquidation Preference Series A 10,200 10,200 $ 0.04167 $ 421 $ 425 Series A-1 22,369 22,369 0.09164 2,000 2,050 Series B 42,360 42,052 0.21580 10,533 9,075 Series C 39,600 36,080 0.33452 12,049 12,069 Series D 30,000 29,150 1.47513 42,811 43,000 Total 144,529 139,851 $ 67,814 $ 66,619 Redeemable Convertible Preferred Stock Warrants As of December 31, 2014 and immediately prior to the completion of the IPO, the Company had the following redeemable convertible preferred stock warrants issued and outstanding (in thousands, except per share data): Warrant Class: Number of Shares Underlying Warrants Fair Value Issuance Date Exercise Series B 278 2,351 June 2011 $ 0.22 Series C 57 475 April 2012 0.33 Series C 1,215 9,728 September 2012 0.67 Series C (1) 405 3,243 September 2012 0.67 Total 1,955 $ 15,797 (1) Represents additional shares that may be exercised pursuant to the Series C redeemable convertible preferred stock warrant issued in September 2012 due to a draw down on a debt financing arrangement in March 2013. Immediately prior to the completion of the IPO, the Company issued 274,992 shares of Series B redeemable convertible preferred stock and 1,210,591 shares of Series C redeemable convertible preferred stock upon the exercise of 277,992 and 1,251,357 of Series B and Series C redeemable convertible preferred stock warrants, respectively, after the forfeiture of 3,000 and 40,766 Series B and Series C redeemable convertible preferred stock warrants, respectively. The shares issued upon the net exercise were sold as Class A common stock in the IPO. In addition, all of the remaining outstanding redeemable convertible preferred stock warrants automatically converted to Class B common stock warrants upon closing of the IPO. As a result of the net exercise of redeemable convertible preferred stock warrants and automatic conversion of the remaining warrants to Class B common stock warrants, the Company revalued the warrants as of the completion of the IPO and reclassified the remaining redeemable convertible preferred stock warrant liability balance related to the unexercised warrants to additional paid-in capital. All remaining outstanding Class B common stock warrants were exercised subsequent to the IPO and as of December 31, 2015, there were no longer any Class B common stock warrants outstanding. Prior to the IPO, as the redeemable convertible preferred stock warrants were exercisable into contingently redeemable preferred shares, the Company had recognized a liability for the fair value of its warrants upon issuance and subsequently remeasured the liability at the end of each reporting period. The Company estimated the fair values of the redeemable convertible preferred stock warrants using the Black-Scholes option-pricing model based on inputs as of the valuation measurement dates, including the fair values of our convertible preferred stock, the estimated volatility of the price of our convertible preferred stock, the expected term of the warrants, and the risk-free interest rates. The key assumptions used in the Black-Scholes option-pricing model for the revaluation of the redeemable convertible preferred stock warrants were as follows: Year Ended December 31, 2015 2014 2013 Expected term (in years) 0.5 0.8 – 1.3 0.6 – 6.9 Volatility 81.3% 46.7 – 54.9% 31.2 – 62.7% Risk-free interest rate 0.1% 0.1 – 0.2% 0.1 – 2.5% Dividend yield —% —% —%

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stockholders' Equity	Stockholders’ Equity Preferred Stock Upon completion of its IPO on June 22, 2015, the Company filed a Restated Certificate of Incorporation, which authorized the issuance of preferred stock with rights and preferences, including voting rights, designated from time to time by the board of directors. As of December 31, 2015 , there were 10,000,000 shares of preferred stock authorized with a par value of $0.0001 per share, and no shares of preferred stock issued or outstanding. Common Stock In connection with the IPO, the Company established two classes of authorized common stock, Class A common stock and Class B common stock. All shares of common stock outstanding immediately prior to the IPO were converted into an equivalent amount of shares of Class B common stock. As of December 31, 2015, the Company had 600,000,000 shares of Class A common stock authorized with a par value of $0.0001 per share and 350,000,000 shares of Class B common stock authorized with a par value of $0.0001 per share. As of December 31, 2015, 99,416,351 shares of Class A common stock were issued and outstanding and 115,365,222 shares of Class B common stock were issued and outstanding. As of December 31, 2014, the Company had 230,400,000 shares of common stock authorized for issuance and 40,875,583 shares issued and outstanding. Holders of Class A common stock are entitled to one vote for each share of Class A common stock held on all matters submitted to a vote of stockholders and holders of Class B common stock are entitled to ten votes for each share of Class B common stock held on all matters submitted to a vote of stockholders. Except with respect to voting, the rights of the holders of Class A and Class B common stock are identical. Shares of Class B common stock are voluntarily convertible into shares of Class A common stock at the option of the holder and generally automatically convert into shares of our Class A common stock upon a transfer. 2007 Equity Incentive Plan In September 2007, the Company adopted the Amended and Restated 2007 Stock Plan (the “2007 Plan”), which was most recently amended in March 2015. The 2007 Plan provides for the grant of incentive and non-statutory stock options and RSUs to employees, directors, and consultants under terms and provisions established by the board of directors. The board of directors determines the period over which the options vest and become exercisable. Options granted under the 2007 Plan are generally subject to a four -year vesting period, with 25% vesting after a one -year period and monthly vesting thereafter. Options expire after ten years. The exercise price of incentive stock options granted under the 2007 Plan must be at least equal to 100% of the fair value of the common stock at the date of grant, as determined by the board of directors. The exercise price of non-statutory options granted under the 2007 Plan must be at least equal to 85% of the fair value of the common stock at the date of grant, as determined by the board of directors. RSUs granted under the 2007 Plan are generally subject to a three - or four -year vesting period with annual vesting. The 2015 Equity Incentive Plan (the “2015 Plan”) became effective on June 16, 2015. As a result, the Company will not grant any additional stock options under the 2007 Plan and the 2007 Plan has terminated. Any outstanding stock options and RSUs granted under the 2007 Plan will remain outstanding, subject to the terms of the 2007 Plan and applicable award agreements, until such shares are issued under those awards, by exercise of stock options or settlement of RSUs, or until the awards terminate or expire by their terms. Stock options and RSUs granted under the 2007 Plan generally have terms similar to those described below with respect to stock options and RSUs granted under the 2015 Plan. 2015 Equity Incentive Plan In May 2015, the Company’s board of directors and stockholders adopted and approved the 2015 Plan. The 2015 Plan became effective on June 16, 2015 and serves as the successor to the 2007 Plan. The remaining shares available for issuance under the 2007 Plan became reserved for issuance under the 2015 Plan, and the Company ceased granting awards under the 2007 Plan. The number of shares reserved for issuance under the 2015 Plan will increase automatically on the first day of January of each year starting in 2016 through 2025 by the number of shares of Class A common stock equal to 5% of the total outstanding shares of common stock as of the immediately preceding December 31. The share reserve may also increase to the extent that outstanding awards expire or terminate un-exercised. As of December 31, 2015, 3,685,100 shares were available for grant under the 2015 Plan. The 2015 Plan authorizes the award of stock options, restricted stock awards, stock appreciation rights, RSUs, performance awards, and stock bonuses to employees, directors, consultants, independent contractors, and advisors. In general, stock options and RSUs will vest over a four -year period, and have a maximum term of ten years. The exercise price of an option will be not less than 100% of the fair market value of the shares on the date of grant. 2015 Employee Stock Purchase Plan In May 2015, the Company’s board of directors adopted the 2015 Employee Stock Purchase Plan (“2015 ESPP”), which became effective on June 17, 2015. A total of 3,750,000 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 at a discount through payroll deductions of up to 15% of eligible compensation, subject to any plan limitations. 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 will end in May 2016. On each purchase date, eligible employees will purchase Class A common stock at a price per share equal to 85% of the lesser of the fair market value of the Company’s Class A common stock (i) on the first trading day of the applicable offering period and (ii) the last trading day of each purchase period in the applicable offering period. For the first offering period, which began on June 17, 2015, the fair market value of the Class A common stock on the offering date was $20.00 , the price at which the Company’s Class A common stock was first sold to the public in its IPO, as specified in the final prospectus filed with the SEC on June 18, 2015, pursuant to Rule 424(b). Stock Options Activity under the 2007 Plan and 2015 Plan is as follows (in thousands except per share amounts): Options Outstanding Number of Shares Subject to Options Weighted– Average Exercise Price Aggregate Intrinsic Value Balance—December 31, 2012 20,947 $ 0.06 Granted 6,476 0.61 Exercised (3,283 ) 0.05 $ 1,111 Canceled (736 ) 0.16 Balance—December 31, 2013 23,404 0.21 Granted 22,094 3.25 Exercised (735 ) 0.14 $ 3,001 Canceled (765 ) 0.95 Balance—December 31, 2014 43,998 1.72 $ 207,863 Granted 6,950 10.67 Exercised (5,397 ) 0.74 $ 173,507 Canceled (1,189 ) 3.21 Balance—December 31, 2015 44,362 3.20 $ 1,171,688 Options exercisable—December 31, 2015 20,763 0.99 $ 593,810 Options vested and expected to vest—December 31, 2015 43,502 3.16 $ 1,150,881 The aggregate intrinsic values of options outstanding, exercisable, vested and expected to vest were calculated as the difference between the exercise price of the options and the estimated fair value of the Company’s common stock, as determined by the board of directors, as of December 31, 2014 and the fair value of the Class A common stock of $29.59 as of December 31, 2015. The total grant date fair value of options that vested during 2015, 2014, 2013 was $18.6 million , $1.7 million , and $0.3 million , respectively. Restricted Stock Units RSU activity under the equity incentive plans is as follows: RSUs Outstanding Weighted- Average Grant Date Fair Value (in thousands) Unvested balance—December 31, 2014 — $ — Granted 3,326 34.27 Forfeited or canceled (34 ) 34.26 Unvested balance—December 31, 2015 3,292 34.27 Stock-Based Compensation Expense Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2015 2014 2013 Cost of revenue $ 4,739 $ 890 $ 37 Research and development 18,251 2,350 288 Sales and marketing 7,419 1,295 204 General and administrative 10,615 2,269 91 Total stock-based compensation expense $ 41,024 $ 6,804 $ 620 The weighted-average grant date fair value of stock options granted during 2015, 2014, and 2013 was $10.67 , $2.40 , and $0.52 per share, respectively. As of December 31, 2015, the total unrecognized compensation expense related to unvested options, net of estimated forfeitures, was $78.2 million , which the Company expects to recognize over an estimated weighted average period of 2.9 years , respectively. As of December 31, 2015, the total unrecognized compensation expense related to unvested RSUs, net of estimated forfeitures, was $96.6 million , which the Company expects to recognize over an estimated weighted average period of 3.5 years . As of December 31, 2015, the total unrecognized compensation expense related to unvested common stock issued in connection with the FitStar acquisition, net of estimated forfeitures, was $1.7 million , which the Company expects to recognize over an estimated weighted average period of 2.2 years . Stock-based compensation is measured at the grant date based on the fair value of the award and is recognized as expense, net of estimated forfeitures, over the requisite service period, which is generally the vesting period of the respective award. The fair value of RSUs is the fair value of the Company’s Class A common stock on the grant date. In determining the fair value of the options and the equity awards issued under the 2015 ESPP, the Company uses the Black-Scholes option-pricing model and assumptions discussed below. Each of these inputs is subjective and generally requires significant judgment. Fair Value of Common Stock —The fair value of the shares of common stock underlying stock options has historically been established by the Company’s board of directors, which is responsible for these estimates, and has been based in part upon a valuation provided by an independent third-party valuation firm. Because there has been no public market for the Company’s common stock, its board of directors considered this independent valuation and other factors, including, but not limited to, revenue growth, the current status of the technical and commercial success of its operations, its financial condition, the stage of development and competition to establish the fair value of the Company’s common stock at the time of grant of the option. The fair value of the underlying common stock will be determined by the board of directors until such time as its common stock is listed on a stock exchange. Following the completion of the IPO, the Company began using the market closing price for Class A common stock as reported on the New York Stock Exchange. Expected Term —The expected term represents the period over which the Company anticipates stock-based awards to be outstanding. The Company does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate expected term due to the limited period of time stock-based awards have been exercisable. As a result, for stock options, the Company used the simplified method to calculate the expected term estimate based on the vesting and contractual terms of the option. Under the simplified method, the expected term is equal to the average of the stock-based award’s weighted average vesting period and its contractual term. The expected term of the 2015 ESPP is based on the contractual term. Volatility —Expected volatility is a measure of the amount by which the stock price is expected to fluctuate. The Company estimates the expected volatility of the common stock underlying its stock options at the grant date by taking the average historical volatility of the common stock of a group of comparable publicly traded companies over a period equal to the expected life of the options. Risk-Free Rate —The risk-free interest rate is estimated average interest rate based on U.S. Treasury zero-coupon notes with terms consistent with the expected term of the awards. Dividend Yield —The Company has never declared or paid any cash dividends and does not presently plan to pay cash dividends in the foreseeable future. Consequently, it used an expected dividend yield of zero. In addition, the Company is required to estimate the amount of stock-based compensation that it expects to be forfeited based on historical experience. The assumptions used in calculating the fair value of the stock-based awards represent management judgment. As a result, if factors change and different assumptions are used, the stock-based compensation expense could be materially different in the future. The fair value of the stock option awards and awards issued under the 2015 ESPP granted to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2015 2014 2013 Employee stock options Expected term (in years) 6.25 6.25 6.00 – 6.25 Volatility 52.1% - 56.9% 54.83% – 60.94% 60.57% – 62.03% Risk-free interest rate 1.5% - 1.9% 1.73% – 2.04% 1.04% – 1.93% Dividend yield —% —% —% Employee stock purchase plan Expected term (in years) 0.5 – 0.9 — — Volatility 27.7% - 35.0% —% —% Risk-free interest rate 0.3% —% —% Dividend yield —% —% —%

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands): Year Ended December 31, 2015 2014 2013 United States $ 278,250 $ 150,137 $ (13,779 ) Foreign 9,699 (10,364 ) 94 Total $ 287,949 $ 139,773 $ (13,685 ) The income tax expense is composed of the following (in thousands): Year Ended December 31, 2015 2014 2013 Current: Federal $ 140,396 $ 47,565 $ 31,176 State 13,307 2,319 6,736 Foreign 1,107 113 25 Total current 154,810 49,997 37,937 Deferred: Federal (33,421 ) (39,339 ) — State (8,941 ) (2,651 ) — Foreign (176 ) (11 ) — Total deferred (42,538 ) (42,001 ) — Total income tax expense $ 112,272 $ 7,996 $ 37,937 The reconciliation of the Company’s effective tax rate to the statutory federal rate is as follows: Year Ended December 31, 2015 2014 2013 Tax at federal statutory rate 35.0 % 35.0 % (35.0 )% State taxes, net of federal effect 1.5 (0.2 ) 32.0 Foreign rate differential (0.8 ) 2.7 (0.1 ) Tax credits (2.0 ) (1.1 ) (9.6 ) Domestic production activities deduction (3.3 ) (2.6 ) (12.7 ) Warrant fair value adjustment 6.9 3.3 8.6 Stock-based compensation 1.7 — — Change in valuation allowance — (32.0 ) 292.6 Other — 0.6 1.4 Effective tax rate 39.0 % 5.7 % 277.2 % For 2015, the Company recorded an expense for income taxes of $112.3 million , for an effective tax rate of 39.0% . The effective tax rate is higher than the statutory federal tax rate primarily due to state taxes, net of federal benefit and certain permanent differences related to the non-deductible 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 the change in contingent consideration from the FitStar acquisition and a permanent domestic production activities deduction. For 2014, the Company recorded an expense for income taxes of $8.0 million , for an effective tax rate of 5.7% . The tax expense in 2014 reflects tax benefits of $51.3 million from the full release of the Company’s deferred income tax asset valuation allowance, of which $6.4 million related to a state tax benefit, partially offset by income tax expense on earnings. The tax effects of temporary differences that give rise to significant portions of the deferred tax assets were as follows (in thousands): December 31, 2015 2014 Net operating losses and credits $ 5,225 $ 1,331 Fixed assets and intangible assets 1,227 2,436 Accruals and reserves 54,891 23,331 Fitbit Force recall reserve 1,910 8,159 Stock-based compensation 9,642 1,306 Other 10,566 5,438 Gross deferred tax assets 83,461 42,001 Debt issuance costs (441 ) — Net deferred tax assets $ 83,020 $ 42,001 In November 2015, the FASB issued ASU 2015-17, “Balance Sheet Classification of Deferred Taxes,” which simplifies the presentation of deferred income taxes. This ASU requires that deferred tax assets and liabilities be classified as non-current in a statement of financial position. The Company early adopted ASU 2015-17 retrospectively in its fourth quarter of 2015 and reclassified all of its current deferred tax assets to noncurrent deferred tax assets on the consolidated balance sheets for all periods presented. The Company accounts for deferred taxes under ASC Topic 740, “Income Taxes” (“ASC 740”) which involves weighing positive and negative evidence concerning the realizability of the Company’s deferred tax assets in each jurisdiction. The Company evaluated its ability to realize the benefit of its net deferred tax assets and weighed all available positive and negative evidence both objective and subjective in nature. In determining the need for a valuation allowance, the weight given to positive and negative evidence is commensurate with the extent to which the evidence may be objectively verified. Consideration was given to negative evidence such as: the duration and severity of losses in prior years, high seasonal revenue concentrations, increasing competitive pressures, and a challenging retail environment. However, after considering three consecutive years of revenue growth and a three-year cumulative income position as of September 30, 2014, the Company believes the weight of the objectively verifiable positive evidence is sufficient to overcome the weight of any negative evidence. Accordingly, for 2014, based on its assessment of the realizability of its deferred tax assets, the Company released the valuation allowance against all of its U.S. deferred tax assets which resulted in a tax benefit of $51.3 million . As of December 31, 2015 , the Company continued to believe that it was more-likely-than-not that it would have future taxable income sufficient to realize the benefit of the Company’s net deferred tax assets. As a result of certain realization requirements of ASC 718, the table of deferred tax assets and liabilities does not include certain deferred tax assets as of December 31, 2015, that arose directly from tax deductions related to equity compensation that are greater than the compensation recognized for financial reporting. Equity will be increased by $25.1 million for foreign tax purposes, if and when such deferred tax assets are ultimately realized. The Company uses tax law ordering when determining when excess tax benefits have been realized. As of December 31, 2015, the Company has federal net operating loss carryforwards of $5.8 million which expire beginning in 2033, California net operating loss carryforwards of $5.7 million which expire beginning in 2033, and United Kingdom net operating loss carryforwards of $25.1 million which do not expire. As of December 31, 2015 , the Company has federal research credit carryforwards of approximately $0.2 million , which if not utilized, begin to expire in 2028 and California research credit carryforwards of approximately $6.4 million , which do not expire. Utilization of the net operating loss and tax credit carry forwards are subject to an annual limitation due to the ownership percentage change limitations provided by the Internal Revenue Code of 1986 and similar state provisions. The annual limitation may result in the expiration of the net operating loss before utilization. The Company completed FitStar, Inc.'s Section 382 analysis through March 2015 and determined that an ownership change, as defined under Section 382 of the Internal Revenue Code, occurred in March 2015. The Company does not expect the limitation to result in a reduction in total amount utilizable. It is the intention of the Company to indefinitely reinvest the earnings of the Company’s foreign subsidiaries. The Company does not provide for U.S. income taxes on the earnings of its foreign subsidiaries as such earnings are to be reinvested indefinitely. If these earnings were distributed to the United States in the form of dividends or otherwise or if the shares of the relevant foreign subsidiaries were sold or otherwise transferred the Company would be subject to additional U.S. income taxes, subject to adjustment for foreign tax credits, and foreign withholding taxes. As of December 31, 2015 , there was $1.6 million of cumulative foreign earnings upon which U.S. income taxes have not been provided. As of December 31, 2015 and 2014, the Company has $23.5 million and $10.6 million of unrecognized tax benefits. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): December 31, 2015 2014 2013 Balance at beginning of year $ 10,594 $ 7,991 $ 634 Reductions based on tax positions related to prior year (18 ) (418 ) (87 ) Additions based on tax positions related to current year 12,942 3,021 7,444 Balance at end of year $ 23,518 $ 10,594 $ 7,991 At December 31, 2015 , the total amount of gross unrecognized tax benefits was $23.5 million , all of which would affect the effective tax rate if recognized. The Company does not have any tax positions as of December 31, 2015 for which it is reasonably possible the total amount of gross unrecognized tax benefits will increase or decrease within the following 12 months . The Company’s policy is to record interest and penalties related to unrecognized tax benefits as income tax expense. During 2015 and 2014, the Company recorded $0.6 million and $0.3 million related to the accrual of interest and penalties. The Company is subject to taxation in the United States and various states and foreign jurisdictions. The material jurisdictions in which the Company is subject to potential examination include the United States and Ireland. The Company believes that adequate amounts have been reserved for these jurisdictions. The Company is under examination by the Internal Revenue Service for the 2013 tax year. For federal, state and non-U.S. tax returns, the Company is generally no longer subject to tax examinations for years prior to 2008.

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2015
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions Softbank Distribution Agreement In December 2012, the Company granted SoftBank BB Corporation (“SoftBank BB”), an entity affiliated with SoftBank PrinceVille Investments, L.P., one of the Company’s investors, a distribution right for the Company’s products in Japan, pursuant to a distribution agreement. The agreement was subsequently amended in December 2014 such that SoftBank BB relinquished its right of exclusivity. For 2014 and 2013, the Company recognized a reduction of $1.7 million to revenue and $17.6 million in revenue, respectively related to SoftBank BB. The Company also recognized $0.1 million in expenses related to SoftBank BB in 2013. During 2014, product sales to SoftBank BB were $1.2 million . However the Company accepted sales returns of $2.9 million due to the amendment of the distribution agreement. An additional refund of $0.3 million was paid to SoftBank BB in 2015, and no amounts were due to either party as of December 31, 2015.

Net Income (Loss) per Share Att

Net Income (Loss) per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2015
Earnings Per Share [Abstract]
Net Income (Loss) per Share Attributable to Common Stockholders	Net Income (Loss) per Share Attributable to Common Stockholders The following table sets forth the computation of the Company’s basic and diluted net income (loss) per share attributable to common stockholders (in thousands, except per share amounts): Year Ended December 31, 2015 2014 2013 Numerator: Net income (loss) $ 175,677 $ 131,777 $ (51,622 ) Less: noncumulative dividends to preferred stockholders (2,526 ) (5,326 ) — Less: undistributed earnings to participating securities (59,133 ) (98,103 ) — Net income (loss) attributable to common stockholders—basic 114,018 28,348 (51,622 ) Add: adjustments to undistributed earnings to participating securities 8,821 10,175 — Net income (loss) attributable to common stockholders—diluted $ 122,839 $ 38,523 $ (51,622 ) Denominator: Weighted-average shares of common stock—basic for Class A and Class B 129,886 40,351 39,179 Effect of dilutive securities 34,327 20,828 — Weighted-average shares of common stock—diluted for Class A and Class B 164,213 61,179 39,179 Net income (loss) per share attributable to common stockholders: Basic $ 0.88 $ 0.70 $ (1.32 ) Diluted $ 0.75 $ 0.63 $ (1.32 ) The following common stock equivalents (in thousands) were excluded from the computation of diluted net income (loss) per share for the periods presented because including them would have been antidilutive: December 31, 2015 2014 2013 Redeemable convertible preferred stock 65,903 139,851 139,504 Stock options to purchase common stock 445 4,420 23,440 Restricted stock units 692 — — Redeemable convertible preferred stock warrants 921 1,955 2,302 Total 67,961 146,226 165,246

Significant Customer Informatio

Significant Customer Information and Other Information	12 Months Ended
	Dec. 31, 2015
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 were as follows: December 31, 2015 2014 2013 A 15 % 13 % * B 14 12 14 C 14 11 14 * Revenue was less than 10%. Retailers and distributors that accounted for equal to or greater than 10% of accounts receivable at December 31, 2015 and 2014 were as follows: December 31, 2015 2014 C 23 % 14 % B 19 17 A 15 * D * 13 E * 10 * Accounts receivable were less than 10%. Geographic and Other Information Revenue by geographic region, based on ship-to destinations, was as follows (in thousands): December 31, 2015 2014 2013 United States $ 1,381,152 $ 562,553 $ 206,082 Americas excluding United States 92,252 38,576 9,094 Europe, Middle East, and Africa 208,767 60,699 25,041 APAC 175,827 83,605 30,870 Total $ 1,857,998 $ 745,433 $ 271,087 As of December 31, 2015 and 2014, long-lived assets, which represent property and equipment, located outside the United States were $28.9 million and $20.0 million , respectively.

Acquisition

Acquisition	12 Months Ended
	Dec. 31, 2015
Business Combinations [Abstract]
Acquisition	Acquisition In March 2015, the Company acquired all of the outstanding securities of FitStar, Inc., 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 common stock, net of a repurchase of 24,949 shares, $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 shareholders. The actual amount of this 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 is adjusted at each reporting period, and the change in fair value is included in other income (expense), net on the consolidated statement 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 . The terms related to the contingent consideration have 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 shares of common stock net of a repurchase of 24,948 shares, 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. The Company also recorded acquisition-related transaction costs of $0.3 million , which were included in general and administrative expenses in the consolidated statement of operations during the year ended December 31, 2015. The results of operations of the acquisition are included in the accompanying consolidated statements of operations from the date of acquisition. Pro forma results of operations for this acquisition have not been presented because they are not material to the Company’s consolidated financial statements.

Selected Unaudited Quarterly Fi

Selected Unaudited Quarterly Financial Data	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Selected Unaudited Quarterly Financial Data	Selected Unaudited Quarterly Financial Data The following tables show a summary of the Company’s unaudited quarterly financial information for each of the four quarters of 2015 and 2014 (in thousands, except per share amounts): Three Months Ended December 31, 2015 September 30, 2015 June 30, 2015 March 31, 2015 Revenue $ 711,570 $ 409,262 $ 400,412 $ 336,754 Gross profit $ 348,299 $ 196,013 $ 187,542 $ 169,209 Net income $ 64,165 $ 45,834 $ 17,681 $ 47,997 Net income per share attributable to common stockholders—basic $ 0.30 $ 0.22 $ 0.09 $ 0.26 Net income per share attributable to common stockholders—diluted $ 0.26 $ 0.19 $ 0.07 $ 0.22 Three Months Ended December 31, 2014 September 30, 2014 June 30, 2014 March 31, 2014 Revenue $ 370,184 $ 152,862 $ 113,572 $ 108,815 Gross profit $ 170,894 $ 83,605 $ 58,389 $ 44,769 Net income $ 39,240 $ 68,912 $ 14,753 $ 8,872 Net income per share attributable to common stockholders—basic $ 0.21 $ 0.38 $ 0.07 $ 0.04 Net income per share attributable to common stockholders—diluted $ 0.19 $ 0.34 $ 0.07 $ 0.04

Significant Accounting Polici25

Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Cash and Cash Equivalents	Cash, Cash Equivalents and Marketable Securities Cash and cash equivalents include all cash balances and highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents and marketable securities consist of money market funds, U.S. government and agency securities, commercial paper, and corporate notes and bonds.
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 in stockholders’ equity. Realized gains or losses and other-than-temporary impairments, if any, on available-for-sale securities are reported in other expense, net as incurred. Realized gains and losses on the sale of securities are determined by specific identification of each security’s cost basis. Investments are reviewed periodically to identify possible other-than-temporary impairments. No impairment loss has been recorded on the securities 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.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Assets and liabilities recorded at fair value on a recurring basis are categorized based upon the level of judgment associated with inputs used to measure their fair values. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the reporting date. The Company estimates fair value by applying the following hierarchy, which prioritizes the inputs used to measure fair value into three levels and bases the categorization within the hierarchy upon the lowest level of input that is available and significant to the fair value measurement: Level 1 —Quoted prices in active markets for identical assets or liabilities; Level 2 —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 for substantially the full term of the assets or liabilities; and Level 3 —Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability.
Foreign Currencies	Foreign Currencies The Company and certain of the Company’s wholly-owned subsidiaries use the U.S. dollar as their functional currency. The Company’s subsidiaries that use the U.S. dollar as their functional currency remeasure local currency denominated monetary assets and liabilities at exchange rates in effect at the end of each period, and inventories, property, plant and equipment and other nonmonetary assets and liabilities at historical rates. Gains and losses from these remeasurements have been included in the Company’s operating results within other expense, net. Local currency transactions of these international operations are remeasured into U.S. dollars at the rates of exchange in effect at the date of the transaction. Foreign currency transaction losses were $ 2.6 million , $2.7 million , and $0.2 million for 2015, 2014, and 2013, respectively. The Company translates the assets and liabilities of its non-U.S. dollar functional currency subsidiaries into U.S. dollars using exchange rates in effect at the end of each period. Revenue and expenses for these subsidiaries are translated using rates that approximate those in effect during the related period. Gains and losses from translations are recognized in foreign currency translation included in accumulated other comprehensive income (loss).
Derivative Instruments	Derivative Instruments The Company accounts for its derivative instruments as either assets or liabilities and carries them at fair value. Derivatives held by the Company that are not designated as hedges are adjusted to fair value through earnings at each reporting date. In addition, the Company enters into derivatives that are accounted for as cash flow hedges. 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 in stockholders’ equity and subsequently reclassifies the gains or losses into revenue and operating expenses when the underlying hedged transactions are recognized. The Company periodically assesses the effectiveness of its cash flow hedges. The fair value of derivative assets and liabilities are included in prepaid expenses and other current assets and accrued liabilities on the consolidated balance sheets.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, accounts receivables, and derivative instruments. Cash and cash equivalents are deposited with high quality financial institutions and may, at times, exceed federally insured limits. Management believes that the financial institutions that hold the Company’s deposits are financially credit worthy and, accordingly, minimal credit risk exists with respect to those balances. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal interest rate risk. The Company’s accounts receivable are derived from customers located principally in the United States. The Company maintains credit insurance for the majority of its customer balances, performs ongoing credit evaluations of its customers, and maintains allowances for potential credit losses on customers’ accounts when deemed necessary. Credit losses historically have not been significant. The Company continuously monitors customer payments and maintains an allowance for doubtful accounts based on its assessment of various factors including historical experience, age of the receivable balances, and other current economic conditions or other factors that may affect customers’ ability to pay. The Company’s derivative instruments expose it to credit risk to the extent that its counterparties may be unable to meet the terms of the agreements. The Company seeks to mitigate this risk by limiting counterparties to major financial institutions and by spreading the risk across several major financial institutions. In addition, the potential risk of loss with any one counterparty resulting from this type of credit risk is monitored on an ongoing basis.
Supplier Concentration	Supplier Concentration The Company relies on third parties for the supply and manufacture of its products, as well as third-party logistics providers. In instances where these parties fail to perform their obligations, the Company may be unable to find alternative suppliers or satisfactorily deliver its products to its customers on time, if at all.
Inventories	Inventories Inventories consist of finished goods and component parts, which are purchased from contract manufacturers and component suppliers. Inventories are stated at the lower of cost or market on a first-in, first-out basis. The Company assesses the valuation of inventory and periodically writes down the value for estimated excess and obsolete inventory based upon estimates of future demand and market conditions.
Property and Equipment, Net	Property and Equipment, Net Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation and amortization of property and equipment is calculated using the straight-line method over the estimated useful lives of the assets. Cost of maintenance and repairs that do not improve or extend the lives of the respective assets are expensed as incurred. The useful lives of the property and equipment are as follows: Tooling and manufacturing equipment One to three years Furniture and office equipment Three years Purchased software Three years Capitalized internally-developed software Two to three years Leasehold improvements Shorter of remaining lease term or ten years
Internally-Development Software Costs	Internally-Developed Software Costs The Company capitalizes eligible costs to acquire, develop, or modify internal-use software that are incurred subsequent to the preliminary project stage.
Research and Development	Research and Development Research and development expenses consist primarily of personnel-related expenses, consulting and contractor expenses, tooling and prototype materials, and allocated overhead costs. Substantially all of the Company’s research and development expenses are related to developing new products and services and improving existing products and services. To date, research and development expenses have been expensed as incurred, because the period between achieving technological feasibility and the release of products and services for sale has been short and development costs qualifying for capitalization have been insignificant.
Business Combinations	Business Combinations, Goodwill, and Intangible Assets The Company allocates the fair value of purchase consideration to tangible assets, liabilities assumed, and intangible assets acquired based on their estimated fair values. The excess of the fair value of purchase consideration over the fair values of these identifiable assets and liabilities is allocated to goodwill. The allocation of the purchase consideration requires management to make significant estimates and assumptions, especially with respect to intangible assets. These estimates can include, but are not limited to, future expected cash flows from acquired customers, acquired technology, and trade names from a market participant perspective, useful lives, and discount rates. Management’s estimates of fair value are based upon assumptions believed to be reasonable, but which are inherently uncertain and unpredictable and, as a result, actual results may differ from estimates. During the measurement period, which is up to one year from the acquisition date, the Company may record adjustments to the assets acquired and liabilities assumed, with the corresponding offset to goodwill. Upon the conclusion of the measurement period, any subsequent adjustments are recorded to earnings.
Goodwill	The Company assesses goodwill for impairment at least annually during the fourth quarter and whenever events or changes in circumstances indicate that the carrying value of the asset may not be recoverable. Consistent with the determination that the Company has one reporting segment, the Company has determined that there is one reporting unit and tests goodwill for impairment at the entity level. Goodwill is tested using the two-step process in accordance with ASC 350, Intangibles—Goodwill and Other . In the first step, the carrying amount of the reporting unit is compared to the fair value based on the fair value of the Company’s common stock. If the fair value of the reporting unit exceeds the carrying value, goodwill is not considered impaired and no further testing is required. If the carrying value of the reporting unit exceeds the fair value, goodwill is potentially impaired and the second step of the impairment test must be performed. In the second step, the implied fair value of the goodwill, as defined by ASC 350, is compared to its carrying amount to determine the amount of impairment loss, if any.
Intangible Assets	Acquired finite-lived intangible assets are amortized over their estimated useful lives. The Company evaluates the recoverability of intangible assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review indicates that the carrying amount of property and equipment and intangible assets is not recoverable, the carrying amount of such assets is reduced to fair value. The Company has not recorded any such impairment charge during the years presented.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates its long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Recoverability is measured by comparison of the carrying amounts to the expected future undiscounted cash flows attributable to these assets. If it is determined that an asset is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the assets exceeds the expected discounted future cash flows arising from those assets.
Redeemable Convertible Preferred Stock Warranty Liability	Redeemable Convertible Preferred Stock Warrant Liability The Company’s redeemable convertible preferred stock warrants require liability classification and accounting as the underlying preferred stock is considered redeemable as discussed in Note 9. At initial recognition, the warrants are recorded at their estimated fair value. The warrants are subject to remeasurement at each balance sheet date, with changes in fair value recognized as a component of other expense, net. In connection with the Company’s IPO, the Company remeasured the liability at the time of the IPO and then reclassified the redeemable convertible preferred stock warrant liability to additional paid-in capital as these warrants converted to Class B common stock warrants.
Revenue Recognition	Revenue Recognition The Company derives substantially all of its revenue from sales of connected health and fitness devices and accessories. The Company also generates a small portion of revenue from its subscription-based services. The Company recognizes revenue when persuasive evidence of an arrangement exists, delivery has occurred, the sales price is fixed or determinable, and collection is reasonably assured. The Company considers delivery of its products to have occurred once title and risk of loss has been transferred. For customers where transfer of risk of loss is at the customer’s destination, the Company uses estimates to defer sales at the end of the reporting period based on historical experience of average transit time. The Company recognizes revenue, net of estimated sales returns, sales incentives, discounts, and sales tax. The Company generally recognizes revenue for products sold through retailers and distributors on a sell-in basis. The Company enters into multiple element arrangements that include hardware, software, and services. The first deliverable is the hardware and firmware essential to the functionality of the connected health and fitness device delivered at the time of sale. The second deliverable is the software services included with the products, which are provided free of charge and enable users to sync, view, and access real-time data on the Company’s online dashboard and mobile apps. The third deliverable is the embedded right included with the purchase of the device to receive, on a when-and-if-available basis, future unspecified firmware upgrades and features relating to the product’s essential firmware. Commencing in the first quarter of 2015, the Company began accounting for the embedded right as a separate unit of accounting, which is when it believes, through public announcements, it had created an implied obligation to, from time to time, provide future unspecified firmware upgrades and features to the firmware to improve and add new functionality to the health and fitness devices. In addition, the Company occasionally offers a fourth deliverable in bundled arrangements that allows access to subscription-based services related to the Company’s FitStar offering. The Company allocates revenue to all deliverables based on their relative selling prices. The Company uses a hierarchy to determine the selling price to be used for allocating revenue to deliverables: (i) vendor-specific objective evidence (“VSOE”) of fair value, (ii) third-party evidence (“TPE”), and (iii) best estimate of the selling price (“BESP”). The Company’s process for determining its BESP considers multiple factors including consumer behaviors and the Company’s internal pricing model and may vary depending upon the facts and circumstances related to each deliverable. BESP for the health and fitness devices and unspecified upgrade rights reflect the Company’s best estimate of the selling prices if they were sold regularly on a stand-alone basis and comprises the majority of the arrangement consideration. BESP for upgrade rights currently ranges from $1 to $3 . TPE for the online dashboard and mobile apps is currently estimated at $0.99 . VSOE for access to FitStar subscription-based services is based on the price charged when sold separately. Amounts allocated to the connected health and fitness devices are recognized at the time of delivery, provided the other conditions for revenue recognition have been met. Amounts allocated to the online dashboard and mobile apps and unspecified upgrade rights are deferred and recognized on a straight-line basis over their estimated usage period of approximately eight to thirteen months. The Company offers its users the ability to purchase subscription-based services, through which the users receive incremental features, including access to a digital personal trainer, in-depth analytics regarding the user’s personal metrics, or video-based customized workouts. Amounts paid for subscriptions are deferred and recognized ratably over the service period which is typically one year. Revenue from subscription-based services was less than 1% of revenue for all periods presented. In addition, the Company offers access to software and services to certain customers in the corporate wellness program, which includes distribution capabilities, a real-time dashboard, and support services. The Company is currently unable to establish VSOE or TPE for the corporate wellness software and services. BESP for the corporate wellness software and services is determined based on the Company’s internal pricing model for anticipated renewals for existing customers and pricing for new customers. Revenue allocated to the corporate wellness software and services is deferred and recognized on a straight-line basis over the estimated access period of one year, which is the typical service period. Revenue for corporate wellness software and services was less than 1% of revenue for all periods presented. The Company accounts for shipping and handling fees billed to customers as revenue. Sales taxes and value added taxes (“VAT”) collected from customers are remitted to governmental authorities are not included in revenue, and are reflected as a liability on the consolidated balance sheets. Rights of Return, Stock Rotation Rights, and Price Protection The Company offers limited rights of return, stock rotation rights, and price protection under various policies and programs with its retailer and distributor customers and end-users. Below is a summary of the general provisions of such policies and programs: • Certain retailers and distributors are allowed to return products that were originally sold through to an end user, called “open box” returns, and such returns may be made at any time after original sale. • All purchases through Fitbit.com are covered by a 45 -day right of return. • Distributors are allowed stock rotation rights which are limited rights of return of products purchased during a prior period, generally one quarter. • Distributors and retailers are allowed return rights for defective products. • Certain distributors are offered price protection that allows for the right to a partial credit for unsold inventory held by the distributor if the Company reduces the selling price of a product. The Company meets all conditions required to recognize revenue at the time of sale when a right of return exists. For example, the price to the buyer is fixed or determinable at time of sale; the buyer’s obligation to pay is not contingent on resale of the product; and the Company is able to reasonably estimate the amount of future returns. The Company estimates and records reserves for these policies and programs as a reduction of revenue and accounts receivable. On a quarterly basis, the amount of revenue that is reserved for future returns is calculated based on the Company’s historical trends and data specific to each reporting period. The Company reviews the actual returns evidenced in prior quarters as a percent of related revenue to determine the historical returns rate. It then applies the historical returns rate to the current period revenue as a basis for estimating future returns. Through December 31, 2015 , actual returns have primarily been open-box returns. In addition, through December 31, 2015 , the Company has had minimal stock rotation or price protection claims. When necessary, the Company also provides a specific reserve for product in the distribution channel in excess of estimated requirements. This estimate can be affected by the amount of a particular product in the channel, the rate of sell-through, product plans, and other factors. The Company also considers whether there are circumstances which may result in anticipated returns higher than the historical return rate from direct users and records an additional reserve as necessary. Sales Incentives The Company offers sales incentives through various programs, consisting primarily of cooperative advertising and marketing development fund programs. The Company records advertising and marketing development fund programs with customers as a reduction to revenue unless it receives an identifiable benefit in exchange for credits claimed by the customer and can reasonably estimate the fair value of the identifiable benefit received, in which case the Company records it as a marketing expense. The Company recognizes a liability and reduces revenue for rebates or other incentives based on the estimated amount of rebates or credits that will be claimed by customers.
Cost of Revenue	Cost of Revenue Cost of revenue consists of product costs, including costs of contract manufacturers for production, shipping and handling costs, packaging, warranty replacement costs, fulfillment costs, manufacturing and tooling equipment depreciation, warehousing costs, excess and obsolete inventory write-downs, costs related to the Fitbit Force product recall, and certain allocated costs related to management, facilities, and personnel-related expenses and other expenses associated with supply chain logistics.
Advertising Costs	Advertising Costs and Point of Purchase (“POP”) Displays Costs related to advertising and promotions, excluding co-op advertising costs, are expensed to sales and marketing as incurred.
Product Warranty	Product Warranty The Company offers a standard product warranty that the product will operate under normal use for a period of one year from date of original purchase except in the European Union where the Company provides a two -year warranty. The Company has the obligation, at its option, to either repair or replace the defective product. At the time revenue is recognized, an estimate of future warranty costs is recorded as a component of cost of revenues. Factors that affect the warranty obligation include product failure rates, service delivery costs incurred in correcting the product failures, and warranty policies. The warranty obligation does not consider historical experience of the Fitbit Force product as a separate reserve has been established for the Fitbit Force recall. The Company’s products are manufactured by third-party contract manufacturers, and in certain cases, the Company may have recourse to such third-party contract manufacturers.
Fitbit Force Product Recall	Fitbit Force Product Recall The Company established reserves for the Fitbit Force recall when circumstances giving rise to the recall became known. It considered various factors in estimating the product recall exposure. These include estimates for: • refunds and product returns from retailer and distributor customers and end-users, which were charged to revenue and cost of revenue on the consolidated statements of operations; • 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 by the Company’s contract manufacturers, write-offs of tooling and manufacturing equipment, which were charged to cost of revenue on the consolidated statements of operations; and • legal fees and settlement costs, which were charged to general and administrative expenses on the consolidated statements of operations. These factors above are updated and reevaluated each period and the related reserves are adjusted when factors indicate that the recall reserves are either insufficient to cover or exceed the estimated product recall expenses.
Share-Based Compensation	Stock-Based Compensation The Company measures its stock-based awards made to employees based on the estimated fair values of the awards as of the grant date using the Black-Scholes option-pricing model. The fair value of restricted stock units (“RSUs”) is the fair value of the Company’s common stock on the grant date. Stock-based compensation expense is recognized over the requisite service period on a straight-line basis and is recorded net of estimated forfeitures. Stock-based compensation expenses for options granted to non-employees as consideration for services received are measured on the date of performance at the fair value of the consideration received or the fair value of the equity instruments issued, using the Black-Scholes option-pricing model, whichever can be more reliably measured. Stock-based compensation expenses for options granted to non-employees are remeasured as the underlying options vest. The Company recognizes tax benefits related to stock-based compensation to the extent that the total reduction to its income tax liability from stock-based compensation is greater than the amount of the deferred tax assets previously recorded in anticipation of these benefits. The Company recognizes a benefit from stock-based compensation in equity to the extent that an incremental tax benefit is realized by following the ordering provisions of the tax laws.
Segment Information	Segment Information The Company operates as one operating segment as it only reports financial information on an aggregate and consolidated basis to its Chief Executive Officer, who is the Company’s chief operating decision maker.
Income Taxes	Income Taxes The Company utilizes the asset and liability method of accounting for income taxes, which requires the recognition of deferred tax assets and liabilities for expected future consequences of temporary differences between the financial reporting and income tax bases of assets and liabilities using enacted tax rates. The Company makes estimates, assumptions, and judgments to determine its expense for income taxes and also for deferred tax assets and liabilities and any valuation allowances recorded against its deferred tax assets. The Company assesses the likelihood that its deferred tax assets will be recovered from future taxable income and, to the extent it believes that recovery is not likely, the Company establishes a valuation allowance. The calculation of the Company’s income tax expense involves the use of estimates, assumptions, and judgments while taking into account current tax laws, its interpretation of current tax laws, and possible outcomes of future tax audits. The Company has established reserves to address potential exposures related to tax positions that could be challenged by tax authorities. Although the Company believes its estimates, assumptions, and judgments to be reasonable, any changes in tax law or its interpretation of tax laws and the resolutions of potential tax audits could significantly impact the amounts provided for income taxes in its consolidated financial statements. The calculation of the Company’s deferred tax asset balance involves the use of estimates, assumptions, and judgments while taking into account estimates of the amounts and type of future taxable income. Actual future operating results and the underlying amount and type of income could differ materially from the Company’s estimates, assumptions, and judgments, thereby impacting its financial position and operating results. The Company includes interest and penalties related to unrecognized tax benefits within income tax expense. Interest and penalties related to unrecognized tax benefits have been recognized in the appropriate periods presented.
Net Income (Loss) per Share Attributable to Common Stockholders	Net Income (Loss) 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. The Company considers its redeemable convertible preferred stock to be participating securities. The holders of the redeemable convertible preferred stock did not have a contractual obligation to share in losses. 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. 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. 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 common stock 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. In 2013 , basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding during the period without consideration of common stock equivalents or the participation rights of the preferred stock as they do not share in losses. As the Company was in a net loss position in 2013, basic net loss per share attributable to common stockholders is the same as diluted net loss per share attributable to common stockholders as the inclusion of all potential shares of common stock outstanding would have been anti-dilutive.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the 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. ASU 2014-09 is effective for annual periods beginning after December 15, 2016, including interim periods within that period. Early adoption is not permitted. The FASB recently issued an exposure draft of a proposed ASU that would delay the effective date of ASU 2014-09 by one year and allow for early adoption. 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. The Company is currently evaluating the impact of this guidance on its consolidated financial statements.
Principles of Consolidation	Principles of Consolidation The 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 consolidated financial statements in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) requires management to make estimates and assumptions that affect the amounts reported and disclosed in the consolidated financial statements and accompanying notes. The estimates and assumptions made by management related to revenue recognition, accruals for the Fitbit Force recall, reserves for sales returns and incentives, reserves for warranty, valuation of stock options, fair value of warrant liability and derivative assets and liabilities, allowance for doubtful accounts, inventory valuation, 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, 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 consolidated financial statements.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) consists of two components, net income (loss) and other comprehensive income, net of tax. Other comprehensive income refers to revenue, expenses, and gains and losses that are recorded as an element of stockholders’ equity but are excluded from net income (loss). The Company’s other comprehensive income consists of net unrealized gains and losses on derivative instruments accounted for as cash flow hedges, foreign currency translation adjustments from those subsidiaries not using the U.S. dollar as their functional currency, and unrealized gains and losses on available-for-sale securities.

Significant Accounting Polici26

Significant Accounting Policies Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Accounting Policies [Abstract]
Schedule of useful lives of property and equipment	The useful lives of the property and equipment are as follows: Tooling and manufacturing equipment One to three years Furniture and office equipment Three years Purchased software Three years Capitalized internally-developed software Two to three years Leasehold improvements Shorter of remaining lease term or ten years Property and equipment, net, consisted of the following (in thousands): December 31, 2015 2014 Tooling and manufacturing equipment $ 53,092 $ 28,344 Furniture and office equipment 6,809 2,891 Purchased and internally-developed software 3,794 1,396 Leasehold improvements 8,388 3,594 Total property and equipment 72,083 36,225 Less: Accumulated depreciation and amortization (27,582 ) (9,790 ) Property and equipment, net $ 44,501 $ 26,435

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
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): December 31, 2015 Level 1 Level 2 Level 3 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 December 31, 2014 Level 1 Level 2 Level 3 Total Assets: Derivative assets $ — $ 316 $ — $ 316 Liabilities: Redeemable convertible preferred stock warrant liability $ — $ — $ 15,797 $ 15,797 Derivative liabilities — 105 — 105 Total $ — $ 105 $ 15,797 $ 15,902
Schedule of changes in fair value of redeemable convertible preferred stock warrant liability	The following table sets forth a summary of the changes in the fair value of the acquisition-related contingent consideration (in thousands): Balance at December 31, 2014 $ — Addition from acquisition 7,704 Change in fair value of contingent consideration (7,704 ) Balance at December 31, 2015 $ — The following table sets forth a summary of the changes in the fair value of the redeemable convertible preferred stock warrant liability (in thousands): Balance at December 31, 2012 $ 488 Fair value of redeemable convertible preferred stock warrants issued 170 Change in fair value 3,370 Balance at December 31, 2013 4,028 Settlement of warrant liability upon exercise (1,503 ) Change in fair value 13,272 Balance at December 31, 2014 15,797 Change in fair value 56,655 Settlement of warrant liability upon exercise (56,678 ) Reclassification of unexercised warrants to additional paid in capital upon the IPO (15,774 ) Balance at December 31, 2015 $ —

Financial Instruments (Tables)

Financial Instruments (Tables)	12 Months Ended
	Dec. 31, 2015
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Schedule of available for sale securities including fair value and gross unrealized losses	The following table sets forth the 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 presents fair values and gross unrealized losses of investments that have been in an unrealized loss position for less than twelve months as of December 31, 2015 (in thousands): Fair Value Gross Unrealized Losses U.S. government agencies $ 113,314 $ (4 ) Corporate debt securities 193,964 (55 ) Total $ 307,278 $ (59 )
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 dates presented (in thousands): December 31, 2015 December 31, 2014 Balance Sheet Location Fair Value Derivative Assets Fair Value Derivative Liabilities Fair Value Derivative Assets Fair Value Derivative Liabilities Cash flow designated hedges Prepaid expense and other current assets $ 3,116 $ — $ — $ — Cash flow designated hedges Accrued liabilities — 1,327 — — Hedges not designated Prepaid expense and other current assets 2,886 — 316 — Hedges not designated Accrued liabilities — 1,313 — 105 Total fair value of derivative instruments $ 6,002 $ 2,640 $ 316 $ 105
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 (“OCI”) and the consolidated statement of operations for the periods presented (in thousands): Year Ended December 31, Income Statement Location 2015 2014 Foreign exchange cash flow hedges: Gain (loss) recognized in OCI—effective portion $ 2,785 $ — Gain (loss) reclassified from OCI into income—effective portion Revenue 2,183 — Gain (loss) reclassified from OCI into income—effective portion Operating expenses (899 ) — Gain (loss) recognized in income—ineffective portion Other expense, net 202 — Foreign exchange balance sheet hedges: Gain (loss) recognized in income Other expense, net $ 5,861 $ 211
Schedule of offsetting derivative assets	The following table sets forth the available offsetting of net derivative assets under the master netting arrangements as of December 31, 2015 (in thousands): Gross Amounts of Recognized Assets Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Gross Amounts Not Offset in Condensed Consolidated Balance Sheets Financial Instruments Cash Collateral Received Net Amount Foreign exchange contracts $ 6,002 $ — $ 6,002 $ 2,100 $ — $ 3,902
Schedule of offsetting derivative liabilities	The following table sets forth the available offsetting of net derivative liabilities under the master netting arrangements as of December 31, 2015 (in thousands): Gross Amounts of Recognized Liabilities Gross Amounts Offset in the Condensed Consolidated Balance Sheets Net Amounts Presented in Condensed Consolidated Balance Sheets Gross Amounts Not Offset 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)	12 Months Ended
	Dec. 31, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of accounts receivable reserves	Changes in accounts receivable reserves were as follows (in thousands): Allowance for Doubtful Accounts Revenue Reserve Balance at December 31, 2012 $ 92 $ 3,187 Increases 651 20,307 Write-offs/returns taken — (8,078 ) Balance at December 31, 2013 743 15,416 Increases 864 42,740 Write-offs/returns taken (769 ) (31,597 ) Balance at December 31, 2014 838 26,559 Increases 1,115 169,677 Write-offs/returns taken (128 ) (122,191 ) Balance at December 31, 2015 $ 1,825 $ 74,045
Schedule of inventories	Inventories consisted of the following (in thousands): December 31, 2015 2014 Components $ 5,359 $ 53,383 Finished goods 172,787 61,689 Total inventories $ 178,146 $ 115,072
Schedule of prepaid expenses and other current asset	Prepaid expenses and other current assets consisted of the following (in thousands): December 31, 2015 2014 Prepaid income taxes $ 11,889 $ — POP displays, net 9,990 7,121 Derivative assets 6,002 316 Prepaid expenses and other current assets 15,649 6,177 Total prepaid expenses and other current assets $ 43,530 $ 13,614
Schedule of property and equipment	The useful lives of the property and equipment are as follows: Tooling and manufacturing equipment One to three years Furniture and office equipment Three years Purchased software Three years Capitalized internally-developed software Two to three years Leasehold improvements Shorter of remaining lease term or ten years Property and equipment, net, consisted of the following (in thousands): December 31, 2015 2014 Tooling and manufacturing equipment $ 53,092 $ 28,344 Furniture and office equipment 6,809 2,891 Purchased and internally-developed software 3,794 1,396 Leasehold improvements 8,388 3,594 Total property and equipment 72,083 36,225 Less: Accumulated depreciation and amortization (27,582 ) (9,790 ) Property and equipment, net $ 44,501 $ 26,435
Schedule of goodwill	The changes in the carrying amount of goodwill for 2015 were as follows (in thousands). See Note 15 for additional information. Goodwill Balance at December 31, 2014 $ — Goodwill acquired 22,562 Subsequent goodwill adjustments (405 ) Balance at December 31, 2015 $ 22,157
Schedule of intangible assets (excluding goodwill)	The carrying amounts of the intangible assets as of December 31, 2015 were as follows (in thousands, except useful life). See Note 15 for additional information. December 31, 2015 Weighted Average Remaining Useful Life (years) Gross Accumulated Amortization Net Developed technology $ 12,640 $ (1,442 ) $ 11,198 6.3 Trademarks and other 1,278 (260 ) 1,018 4.1 Total intangible assets, net $ 13,918 $ (1,702 ) $ 12,216
Schedule of estimated future amortization expense	The estimated future amortization expense of acquired intangible assets to be charged to cost of revenue and operating expenses after 2015, is as follows (in thousands): Cost of Revenue Operating Expenses Total 2016 $ 1,806 $ 281 $ 2,087 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 intangible assets, net $ 11,198 $ 1,018 $ 12,216
Schedule of accrued liabilities	Accrued liabilities consisted of the following (in thousands): December 31, 2015 2014 Product warranty $ 40,212 $ 20,098 Accrued sales and marketing 33,389 154 Accrued co-op advertising and marketing development funds 29,077 7,679 Employee related liabilities 27,394 4,115 Accrued sales incentives 24,324 3,426 Accrued manufacturing expense and freight 10,723 16,229 Sales taxes and VAT payable 8,349 2,291 Inventory received but not billed 4,292 6,242 Accrued legal fees 3,138 678 Derivative liabilities 2,640 105 Customer deposits 2,062 6,391 Other 9,377 3,532 Accrued liabilities $ 194,977 $ 70,940
Schedule of product warranty reserves	Product warranty reserve activities were as follows (in thousands): Reserve For Product Warranty (1) Balance at December 31, 2012 $ 2,232 Charged to cost of revenue 9,078 Settlement of claims (2,830 ) Balance at December 31, 2013 8,480 Charged to cost of revenue 19,462 Settlement of claims (7,844 ) Balance at December 31, 2014 20,098 Charged to cost of revenue 55,642 Changes in estimate related to pre-existing warranties (8,968 ) Settlement of claims (26,560 ) Balance at December 31, 2015 $ 40,212 (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): Reserve For Fitbit Force Recall Balance at December 31, 2012 $ — Charged to revenue 30,607 Charged to cost of revenue 49,493 Charged to general and administrative 2,838 Settlement of claims — Balance at December 31, 2013 82,938 Charged to revenue 8,112 Charged to cost of revenue 11,339 Charged to general and administrative 505 Settlement of claims (80,418 ) Balance at December 31, 2014 22,476 Benefit to cost of revenue (5,755 ) Benefit to general and administrative (1,174 ) Settlement of claims (10,425 ) Balance at December 31, 2015 $ 5,122
Schedule of accumulated other comprehensive income	The components and activity of accumulated other comprehensive income (“AOCI”), net of tax, were as follows (in thousands): Unrealized Gains on Cash Flow Hedges Currency Translation Adjustments Unrealized Gains (Losses) on Available-for-Sale Investments Total Balance at December 31, 2014 $ — $ 37 $ — $ 37 Other comprehensive income (loss) before reclassifications 1,276 (42 ) (63 ) 1,171 Amounts reclassified from AOCI (525 ) — 8 (517 ) Other comprehensive income (loss) 751 (42 ) (55 ) 654 Balance at December 31, 2015 $ 751 $ (5 ) $ (55 ) $ 691

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]
Schedule of future minimum rental payments for operating leases	Future minimum payments under the leases as of December 31, 2015 were as follows (in thousands): Year ending December 31, Amounts 2016 $ 16,843 2017 20,825 2018 19,835 2019 18,789 2020 15,312 Thereafter 52,020 Total $ 143,624

Redeemable Convertible Prefer31

Redeemable Convertible Preferred Stock and Warrants (Tables)	12 Months Ended
	Dec. 31, 2015
Temporary Equity Disclosure [Abstract]
Schedule of redeemable convertible preferred stock	In connection with the closing of the Company’s IPO, all shares of the Company’s then-outstanding redeemable convertible preferred stock automatically converted on a one -for-one basis into an aggregate of 139,851,483 shares of Class B common stock. Redeemable convertible preferred stock outstanding as of December 31, 2014 and immediately prior to the conversion into Class B common stock and December 31, 2014 consisted of the following (in thousands, except per share data): Shares Authorized Shares Outstanding Price per Share Net Carrying Value Liquidation Preference Series A 10,200 10,200 $ 0.04167 $ 421 $ 425 Series A-1 22,369 22,369 0.09164 2,000 2,050 Series B 42,360 42,052 0.21580 10,533 9,075 Series C 39,600 36,080 0.33452 12,049 12,069 Series D 30,000 29,150 1.47513 42,811 43,000 Total 144,529 139,851 $ 67,814 $ 66,619
Schedule of redeemable convertible preferred stock warrants issued and outstanding	As of December 31, 2014 and immediately prior to the completion of the IPO, the Company had the following redeemable convertible preferred stock warrants issued and outstanding (in thousands, except per share data): Warrant Class: Number of Shares Underlying Warrants Fair Value Issuance Date Exercise Series B 278 2,351 June 2011 $ 0.22 Series C 57 475 April 2012 0.33 Series C 1,215 9,728 September 2012 0.67 Series C (1) 405 3,243 September 2012 0.67 Total 1,955 $ 15,797 (1) Represents additional shares that may be exercised pursuant to the Series C redeemable convertible preferred stock warrant issued in September 2012 due to a draw down on a debt financing arrangement in March 2013.
Schedule of fair value assumptions on redeemable convertible preferred stock warrants	The key assumptions used in the Black-Scholes option-pricing model for the revaluation of the redeemable convertible preferred stock warrants were as follows: Year Ended December 31, 2015 2014 2013 Expected term (in years) 0.5 0.8 – 1.3 0.6 – 6.9 Volatility 81.3% 46.7 – 54.9% 31.2 – 62.7% Risk-free interest rate 0.1% 0.1 – 0.2% 0.1 – 2.5% Dividend yield —% —% —%

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of stock option activity	Activity under the 2007 Plan and 2015 Plan is as follows (in thousands except per share amounts): Options Outstanding Number of Shares Subject to Options Weighted– Average Exercise Price Aggregate Intrinsic Value Balance—December 31, 2012 20,947 $ 0.06 Granted 6,476 0.61 Exercised (3,283 ) 0.05 $ 1,111 Canceled (736 ) 0.16 Balance—December 31, 2013 23,404 0.21 Granted 22,094 3.25 Exercised (735 ) 0.14 $ 3,001 Canceled (765 ) 0.95 Balance—December 31, 2014 43,998 1.72 $ 207,863 Granted 6,950 10.67 Exercised (5,397 ) 0.74 $ 173,507 Canceled (1,189 ) 3.21 Balance—December 31, 2015 44,362 3.20 $ 1,171,688 Options exercisable—December 31, 2015 20,763 0.99 $ 593,810 Options vested and expected to vest—December 31, 2015 43,502 3.16 $ 1,150,881
Schedule of restricted stock unit activity	RSU activity under the equity incentive plans is as follows: RSUs Outstanding Weighted- Average Grant Date Fair Value (in thousands) Unvested balance—December 31, 2014 — $ — Granted 3,326 34.27 Forfeited or canceled (34 ) 34.26 Unvested balance—December 31, 2015 3,292 34.27
Schedule of stock-based compensation expense	Total stock-based compensation recognized was as follows (in thousands): Year Ended December 31, 2015 2014 2013 Cost of revenue $ 4,739 $ 890 $ 37 Research and development 18,251 2,350 288 Sales and marketing 7,419 1,295 204 General and administrative 10,615 2,269 91 Total stock-based compensation expense $ 41,024 $ 6,804 $ 620
Schedule of options valuation assumptions	The fair value of the stock option awards and awards issued under the 2015 ESPP granted to employees was estimated at the date of grant using a Black-Scholes option-pricing model with the following assumptions: Year Ended December 31, 2015 2014 2013 Employee stock options Expected term (in years) 6.25 6.25 6.00 – 6.25 Volatility 52.1% - 56.9% 54.83% – 60.94% 60.57% – 62.03% Risk-free interest rate 1.5% - 1.9% 1.73% – 2.04% 1.04% – 1.93% Dividend yield —% —% —% Employee stock purchase plan Expected term (in years) 0.5 – 0.9 — — Volatility 27.7% - 35.0% —% —% Risk-free interest rate 0.3% —% —% Dividend yield —% —% —%

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Schedule of components of income (loss) before income taxes	The following table presents domestic and foreign components of income (loss) before income taxes for the periods presented (in thousands): Year Ended December 31, 2015 2014 2013 United States $ 278,250 $ 150,137 $ (13,779 ) Foreign 9,699 (10,364 ) 94 Total $ 287,949 $ 139,773 $ (13,685 )
Schedule of components for income tax expense	The income tax expense is composed of the following (in thousands): Year Ended December 31, 2015 2014 2013 Current: Federal $ 140,396 $ 47,565 $ 31,176 State 13,307 2,319 6,736 Foreign 1,107 113 25 Total current 154,810 49,997 37,937 Deferred: Federal (33,421 ) (39,339 ) — State (8,941 ) (2,651 ) — Foreign (176 ) (11 ) — Total deferred (42,538 ) (42,001 ) — Total income tax expense $ 112,272 $ 7,996 $ 37,937
Schedule of reconciliation of effective tax to statutory federal rate	The reconciliation of the Company’s effective tax rate to the statutory federal rate is as follows: Year Ended December 31, 2015 2014 2013 Tax at federal statutory rate 35.0 % 35.0 % (35.0 )% State taxes, net of federal effect 1.5 (0.2 ) 32.0 Foreign rate differential (0.8 ) 2.7 (0.1 ) Tax credits (2.0 ) (1.1 ) (9.6 ) Domestic production activities deduction (3.3 ) (2.6 ) (12.7 ) Warrant fair value adjustment 6.9 3.3 8.6 Stock-based compensation 1.7 — — Change in valuation allowance — (32.0 ) 292.6 Other — 0.6 1.4 Effective tax rate 39.0 % 5.7 % 277.2 %
Schedule of tax effects of temporary differences for deferred tax assets	The tax effects of temporary differences that give rise to significant portions of the deferred tax assets were as follows (in thousands): December 31, 2015 2014 Net operating losses and credits $ 5,225 $ 1,331 Fixed assets and intangible assets 1,227 2,436 Accruals and reserves 54,891 23,331 Fitbit Force recall reserve 1,910 8,159 Stock-based compensation 9,642 1,306 Other 10,566 5,438 Gross deferred tax assets 83,461 42,001 Debt issuance costs (441 ) — Net deferred tax assets $ 83,020 $ 42,001
Schedule of reconciliation of unrecognized tax benefits	As of December 31, 2015 and 2014, the Company has $23.5 million and $10.6 million of unrecognized tax benefits. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands): December 31, 2015 2014 2013 Balance at beginning of year $ 10,594 $ 7,991 $ 634 Reductions based on tax positions related to prior year (18 ) (418 ) (87 ) Additions based on tax positions related to current year 12,942 3,021 7,444 Balance at end of year $ 23,518 $ 10,594 $ 7,991

Net Income (Loss) per Share A34

Net Income (Loss) per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2015
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 (loss) per share attributable to common stockholders (in thousands, except per share amounts): Year Ended December 31, 2015 2014 2013 Numerator: Net income (loss) $ 175,677 $ 131,777 $ (51,622 ) Less: noncumulative dividends to preferred stockholders (2,526 ) (5,326 ) — Less: undistributed earnings to participating securities (59,133 ) (98,103 ) — Net income (loss) attributable to common stockholders—basic 114,018 28,348 (51,622 ) Add: adjustments to undistributed earnings to participating securities 8,821 10,175 — Net income (loss) attributable to common stockholders—diluted $ 122,839 $ 38,523 $ (51,622 ) Denominator: Weighted-average shares of common stock—basic for Class A and Class B 129,886 40,351 39,179 Effect of dilutive securities 34,327 20,828 — Weighted-average shares of common stock—diluted for Class A and Class B 164,213 61,179 39,179 Net income (loss) per share attributable to common stockholders: Basic $ 0.88 $ 0.70 $ (1.32 ) Diluted $ 0.75 $ 0.63 $ (1.32 )
Schedule of antidilutive securities excluded from earnings per share	The following common stock equivalents (in thousands) were excluded from the computation of diluted net income (loss) per share for the periods presented because including them would have been antidilutive: December 31, 2015 2014 2013 Redeemable convertible preferred stock 65,903 139,851 139,504 Stock options to purchase common stock 445 4,420 23,440 Restricted stock units 692 — — Redeemable convertible preferred stock warrants 921 1,955 2,302 Total 67,961 146,226 165,246

Significant Customer Informat35

Significant Customer Information and Other Information (Tables)	12 Months Ended
	Dec. 31, 2015
Risks and Uncertainties [Abstract]
Schedules of concentration of risk	Retailers and distributors with revenue equal to or greater than 10% of total revenue were as follows: December 31, 2015 2014 2013 A 15 % 13 % * B 14 12 14 C 14 11 14 * Revenue was less than 10%. Revenue by geographic region, based on ship-to destinations, was as follows (in thousands): December 31, 2015 2014 2013 United States $ 1,381,152 $ 562,553 $ 206,082 Americas excluding United States 92,252 38,576 9,094 Europe, Middle East, and Africa 208,767 60,699 25,041 APAC 175,827 83,605 30,870 Total $ 1,857,998 $ 745,433 $ 271,087 Retailers and distributors that accounted for equal to or greater than 10% of accounts receivable at December 31, 2015 and 2014 were as follows: December 31, 2015 2014 C 23 % 14 % B 19 17 A 15 * D * 13 E * 10 * Accounts receivable were less than 10%.

Acquisition - (Tables)

Acquisition - (Tables)	12 Months Ended
	Dec. 31, 2015
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

Selected Unaudited Quarterly 37

Selected Unaudited Quarterly Financial Data (Tables)	12 Months Ended
	Dec. 31, 2015
Quarterly Financial Information Disclosure [Abstract]
Schedule of quarterly financial information	The following tables show a summary of the Company’s unaudited quarterly financial information for each of the four quarters of 2015 and 2014 (in thousands, except per share amounts): Three Months Ended December 31, 2015 September 30, 2015 June 30, 2015 March 31, 2015 Revenue $ 711,570 $ 409,262 $ 400,412 $ 336,754 Gross profit $ 348,299 $ 196,013 $ 187,542 $ 169,209 Net income $ 64,165 $ 45,834 $ 17,681 $ 47,997 Net income per share attributable to common stockholders—basic $ 0.30 $ 0.22 $ 0.09 $ 0.26 Net income per share attributable to common stockholders—diluted $ 0.26 $ 0.19 $ 0.07 $ 0.22 Three Months Ended December 31, 2014 September 30, 2014 June 30, 2014 March 31, 2014 Revenue $ 370,184 $ 152,862 $ 113,572 $ 108,815 Gross profit $ 170,894 $ 83,605 $ 58,389 $ 44,769 Net income $ 39,240 $ 68,912 $ 14,753 $ 8,872 Net income per share attributable to common stockholders—basic $ 0.21 $ 0.38 $ 0.07 $ 0.04 Net income per share attributable to common stockholders—diluted $ 0.19 $ 0.34 $ 0.07 $ 0.04

Business Overview - Narrative (

Business Overview - Narrative (Details) $ / shares in Units, $ in Thousands	Jun. 22, 2015USD ($)classshares	Nov. 30, 2015USD ($)$ / sharesshares	Jun. 30, 2015USD ($)$ / sharesshares	Dec. 31, 2015USD ($)classvoteshares	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Class of Stock [Line Items]
Net proceeds from initial public offering | $		$ 84,400	$ 420,900	$ 505,275	$ 0	$ 0
Number of classes of stock | class	2			2
Common Stock [Member]
Class of Stock [Line Items]
Issuance of common stock upon public offering, net of offering costs		3,000,000	22,387,500	25,387,500,000
Shares issued (in shares)				416,929,000
Common Class A [Member]
Class of Stock [Line Items]
Common stock, votes per share | vote				1
Common Class B [Member]
Class of Stock [Line Items]
Issuance of common stock upon public offering, net of offering costs	139,851,483
Common stock, votes per share | vote				10
Common Class B [Member] | Additional Paid-in Capital [Member]
Class of Stock [Line Items]
Reclassification | $			$ 67,800
Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Preferred stock converted and reclassified into Class B Common Stock (in shares)			139,851,483
Series B [Member]
Class of Stock [Line Items]
Shares issued (in shares)	274,992
Series C [Member]
Class of Stock [Line Items]
Shares issued (in shares)	1,210,591
IPO [Member]
Class of Stock [Line Items]
Offering costs incurred | $			$ 5,000
IPO [Member] | Common Stock [Member]
Class of Stock [Line Items]
Share price (in dollars per share) | $ / shares			$ 20
Underwriting discounts and commissions | $			$ 26,900
Offering costs incurred | $			$ 5,000
Over-Allotment Option [Member] | Common Stock [Member]
Class of Stock [Line Items]
Issuance of common stock upon public offering, net of offering costs		2,550,000	5,486,250
Share price (in dollars per share) | $ / shares		$ 29
Underwriting discounts and commissions | $		$ 2,600
Offering costs incurred | $		$ 1,200
Select Stockholders [Member] | IPO [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares sold by certain shareholders (in shares)			19,673,750
Select Stockholders [Member] | Over-Allotment Option [Member] | Common Stock [Member]
Class of Stock [Line Items]
Shares sold by certain shareholders (in shares)		16,550,000
Series B [Member] | Additional Paid-in Capital [Member]
Class of Stock [Line Items]
Reclassification | $	$ 56,700		$ 15,800

Basis of Presentation (Details)

Basis of Presentation (Details) $ in Thousands	May. 27, 2015	Sep. 30, 2014	Jun. 30, 2013	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)
Organization, Consolidation And Presentation Of Financial Statements [Line Items]
Stock split, conversion ratio	1.5	2
Other assets				$ 1,758	$ 1,444
New Accounting Pronouncement, Early Adoption, Effect [Member]
Organization, Consolidation And Presentation Of Financial Statements [Line Items]
Current deferred tax assets					(33,600)
Other assets					$ (8,400)
Redeemable Convertible Preferred Stock [Member]
Organization, Consolidation And Presentation Of Financial Statements [Line Items]
Stock split, conversion ratio			4

Significant Accounting Polici40

Significant Accounting Policies - Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2015
Tooling and manufacturing equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	1 year
Tooling and manufacturing equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Purchased software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Capitalized internally-developed software [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	2 years
Capitalized internally-developed software [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	3 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, useful life	10 years

Significant Accounting Polici41

Significant Accounting Policies - Narrative (Details)	12 Months Ended
	Dec. 31, 2015USD ($)classsegmentvote	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Jun. 22, 2015class
Significant Accounting Policies [Line Items]
Foreign currency transaction losses	$ 2,600,000	$ 2,700,000	$ 200,000
Best estimated selling price upgrade rights	$ 0.99
Product return period	45 days
Advertising and promotion expenses	$ 237,000,000	71,900,000	9,500,000
Cooperative advertising and promotion expense	$ 38,300,000	12,700,000	$ 5,700,000
Product warranty term	1 year
Number of operating segments | segment	1
Number of classes of stock | class	2			2
Other assets	$ 1,758,000	1,444,000
Minimum [Member]
Significant Accounting Policies [Line Items]
Best estimate of the selling price	$ 1
Revenue recognition period	8 months
Maximum [Member]
Significant Accounting Policies [Line Items]
Best estimate of the selling price	$ 3
Revenue recognition period	13 months
European Union [Member]
Significant Accounting Policies [Line Items]
Product warranty term	2 years
Common Class A [Member]
Significant Accounting Policies [Line Items]
Common stock, votes per share | vote	1
Common Class B [Member]
Significant Accounting Policies [Line Items]
Common stock, votes per share | vote	10
Customer Concentration Risk [Member] | Subscription-based Premium Services [Member]
Significant Accounting Policies [Line Items]
Percent of revenue (less than)	1.00%
Customer Concentration Risk [Member] | Corporate Dashboard Tool [Member]
Significant Accounting Policies [Line Items]
Percent of revenue (less than)	1.00%
New Accounting Pronouncement, Early Adoption, Effect [Member]
Significant Accounting Policies [Line Items]
Current deferred tax assets		(33,600,000)
Other assets		$ (8,400,000)

Fair Value Measurements (Detail

Fair Value Measurements (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Liabilities:
Redeemable convertible preferred stock warrant liability	$ 0	$ 15,797
Derivative liabilities	2,640
U.S. government agencies [Member]
Assets:
Available for sale securities	113,314
Corporate debt securities [Member]
Assets:
Available for sale securities	193,964
Fair Value, Measurements, Recurring [Member]
Assets:
Money market funds	248,128
Derivative assets	6,002	316
Total	561,408
Liabilities:
Redeemable convertible preferred stock warrant liability		15,797
Derivative liabilities	2,640	105
Total		15,902
Fair Value, Measurements, Recurring [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	113,314
Fair Value, Measurements, Recurring [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	193,964
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Assets:
Money market funds	248,128
Derivative assets	0	0
Total	248,128
Liabilities:
Redeemable convertible preferred stock warrant liability		0
Derivative liabilities	0	0
Total		0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	0
Fair Value, Measurements, Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	0
Fair Value, Measurements, Recurring [Member] | Level 2 [Member]
Assets:
Money market funds	0
Derivative assets	6,002	316
Total	313,280
Liabilities:
Redeemable convertible preferred stock warrant liability		0
Derivative liabilities	2,640	105
Total		105
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	113,314
Fair Value, Measurements, Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	193,964
Fair Value, Measurements, Recurring [Member] | Level 3 [Member]
Assets:
Money market funds	0
Derivative assets	0	0
Total	0
Liabilities:
Redeemable convertible preferred stock warrant liability		15,797
Derivative liabilities	0	0
Total		$ 15,797
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | U.S. government agencies [Member]
Assets:
Available for sale securities	0
Fair Value, Measurements, Recurring [Member] | Level 3 [Member] | Corporate debt securities [Member]
Assets:
Available for sale securities	$ 0

Fair Value Measurements - Chang

Fair Value Measurements - Changes in fair value (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Redeemable Convertible Preferred Stock Warrant [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of liability, beginning of period	$ 15,797	$ 4,028	$ 488
Change in fair value	56,655	13,272	3,370
Fair value of redeemable convertible preferred stock warrants issued			170
Settlement of warrant liability upon exercise	(56,678)	(1,503)
Reclassification of unexercised warrants to additional paid in capital upon the IPO	(15,774)
Fair value of liability, end of period	0	15,797	$ 4,028
Acquisition Contingent Consideration [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value of liability, beginning of period	0
Addition from acquisition	7,704
Change in fair value	(7,704)
Fair value of liability, end of period	$ 0	$ 0

Financial Instruments - Narrati

Financial Instruments - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Available-for-sale securities in continuous loss position for one year or more, gross unrealized losses	$ 0
Foreign currency exchange contract [Member] | Not designated as hedging instrument [Member]
Derivative [Line Items]
Derivative, notional amount	47,200,000	$ 37,200,000
Cash flow hedges [Member] | Foreign currency exchange contract [Member] | Designated as hedging instrument [Member]
Derivative [Line Items]
Derivative, notional amount based on forecasted revenue	346,600,000
Derivative, notional amount based on forecasted expenses	$ 34,900,000

Financial Instruments - Amortiz

Financial Instruments - Amortized to fair value (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 535,846	$ 195,626	$ 81,728	$ 13,148
Gross Unrealized Gains	4
Gross Unrealized Losses	(59)
Marketable securities	128,632	$ 0
Cash, cash equivalents, and available-for-sale securities, amortized cost	664,533
Fair Value	664,478
Cash [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	109,072
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	248,128
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	63,464
Available-for-sale debt securities, amortized cost	113,315
Gross Unrealized Gains	3
Gross Unrealized Losses	(4)
Available for sale securities	113,314
Marketable securities	49,850
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	115,182
Available-for-sale debt securities, amortized cost	194,018
Gross Unrealized Gains	1
Gross Unrealized Losses	(55)
Available for sale securities	193,964
Marketable securities	$ 78,782

Financial Instruments - Unreali

Financial Instruments - Unrealized loss position (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Schedule of Available-for-sale Securities [Line Items]
Fair Value	$ 307,278
Gross Unrealized Losses	(59)
U.S. government agencies [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	113,314
Gross Unrealized Losses	(4)
Corporate debt securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Fair Value	193,964
Gross Unrealized Losses	$ (55)

Financial Instruments - Financi

Financial Instruments - Financial Position, Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Derivatives, Fair Value [Line Items]
Fair Value Derivative Liabilities	$ 2,640
Foreign currency exchange contract [Member]
Derivatives, Fair Value [Line Items]
Fair Value Derivative Assets	6,002	$ 316
Fair Value Derivative Liabilities	2,640	105
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	3,116	0
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	1,327	0
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	2,886	316
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	$ 1,313	$ 105

Financial Instruments - Stateme

Financial Instruments - Statement of Operations and Other Comprehensive Income (Details) - Foreign currency exchange contract [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Designated as hedging instrument [Member] | Cash flow hedges [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in OCI—effective portion	$ 2,785	$ 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	2,183	0
Other expense, net [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	(899)	0
Other expense, net [Member] | Not designated as hedging instrument [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Gain (loss) recognized in income	5,861	211
Other 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	$ 202	$ 0

Financial Instruments - Offsett

Financial Instruments - Offsetting of Foreign Currency Derivative Contracts (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	$ 2,640
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0
Net Amounts Presented in Condensed Consolidated Balance Sheets	2,640
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	$ 2,100
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Pledged
Net Amount	$ 540
Foreign currency exchange contract [Member]
Offsetting Liabilities [Line Items]
Gross Amounts of Recognized Liabilities	2,640	$ 105
Offsetting Assets [Line Items]
Gross Amounts of Recognized Assets	6,002	$ 316
Gross Amounts Offset in the Condensed Consolidated Balance Sheets	0
Net Amounts Presented in Condensed Consolidated Balance Sheets	6,002
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Financial Instruments	2,100
Gross Amounts Not Offset in Condensed Consolidated Balance Sheets, Cash Collateral Received	0
Net Amount	$ 3,902

Balance Sheet Components - Acco

Balance Sheet Components - Account Receivable Reserves (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Allowance for Doubtful Accounts [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balances	$ 838	$ 743	$ 92
Increases (decrease)	1,115	864	651
Write-offs/returns taken	(128)	(769)	0
Ending balances	1,825	838	743
Revenue Reserve [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balances	26,559	15,416	3,187
Increases (decrease)	169,677	42,740	20,307
Write-offs/returns taken	(122,191)	(31,597)	(8,078)
Ending balances	$ 74,045	$ 26,559	$ 15,416

Balance Sheet Components - Inve

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Components	$ 5,359	$ 53,383
Finished goods	172,787	61,689
Total inventories	$ 178,146	$ 115,072

Balance Sheet Components - Prep

Balance Sheet Components - Prepaid Expenses and Other Current Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Prepaid Taxes	$ 11,889	$ 0
Derivative assets	6,002	316
POP displays, net	9,990	7,121
Prepaid expenses and other current assets	15,649	6,177
Total prepaid expenses and other current assets	$ 43,530	$ 13,614

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 72,083	$ 36,225
Less: Accumulated depreciation and amortization	(27,582)	(9,790)
Property and equipment, net	44,501	26,435
Tooling and manufacturing equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	53,092	28,344
Furniture and office equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	6,809	2,891
Purchased and internally-developed software [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	3,794	1,396
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 8,388	$ 3,594

Balance Sheet Components - Good

Balance Sheet Components - Goodwill Roll forward (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2015USD ($)
Goodwill [Roll Forward]
Balance at December 31, 2014	$ 0
Goodwill acquired	22,562
Subsequent goodwill adjustments	(405)
Balance at December 31, 2015	$ 22,157

Balance Sheet Components - Inta

Balance Sheet Components - Intangible Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-Lived Intangible Assets [Line Items]
Gross	$ 13,918,000
Accumulated Amortization	(1,702,000)
Net	12,216,000	$ 0
Amortization of intangible assets	1,702,000	$ 0	$ 0
Developed technology [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	12,640,000
Accumulated Amortization	(1,442,000)
Net	$ 11,198,000
Weighted Average Remaining Useful Life (years)	6 years 3 months
Trademarks and other [Member]
Finite-Lived Intangible Assets [Line Items]
Gross	$ 1,278,000
Accumulated Amortization	(260,000)
Net	$ 1,018,000
Weighted Average Remaining Useful Life (years)	4 years 1 month 7 days

Balance Sheet Components - Esti

Balance Sheet Components - Estimated Future Amortization Expense (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Finite-Lived Intangible Assets [Line Items]
2,016	$ 2,087,000
2,016	2,036,000
2,017	2,036,000
2,018	2,036,000
2,019	1,853,000
Thereafter	2,168,000
Net	12,216,000	$ 0
Cost of revenue [Member]
Finite-Lived Intangible Assets [Line Items]
2,016	1,806,000
2,016	1,806,000
2,017	1,806,000
2,018	1,806,000
2,019	1,806,000
Thereafter	2,168,000
Net	11,198,000
Operating expenses [Member]
Finite-Lived Intangible Assets [Line Items]
2,016	281,000
2,016	230,000
2,017	230,000
2,018	230,000
2,019	47,000
Thereafter	0
Net	$ 1,018,000

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Product warranty	$ 40,212	$ 20,098
Accrued sales and marketing	33,389	154
Accrued co-op advertising and marketing development funds	29,077	7,679
Employee related liabilities	27,394	4,115
Accrued sales incentives	24,324	3,426
Accrued manufacturing expense and freight	10,723	16,229
Sales taxes and VAT payable	8,349	2,291
Inventory received but not billed	4,292	6,242
Accrued legal fees	3,138	678
Derivative liabilities	2,640	105
Customer deposits	2,062	6,391
Other	9,377	3,532
Accrued liabilities	$ 194,977	$ 70,940

Balance Sheet Components - Prod

Balance Sheet Components - Product Warranty (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Standard and Extended Product Warranty, Increase (Decrease) [Roll Forward]
Beginning balances	$ 20,098	$ 8,480	$ 2,232
Charged to cost of revenue	55,642	19,462	9,078
Changes in estimate related to pre-existing warranties	(8,968)
Settlement of claims	(26,560)	(7,844)	(2,830)
Ending balances	$ 40,212	$ 20,098	$ 8,480

Balance Sheet Components - Rese

Balance Sheet Components - Reserve Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Movement in Valuation Allowances and Reserves [Roll Forward]
Write down on specialized Fitbit Force tooling and manufacturing equipment	$ 5,060	$ 2,964	$ 1,099
Product Recall Reserves [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Beginning balances	22,476	82,938	0
Charged to revenue		8,112	30,607
Charged (benefit) to cost of revenue	(5,755)	11,339	49,493
Charged to general and administrative	(1,174)	505	2,838
Settlement of claims	(10,425)	(80,418)	0
Ending balances	5,122	22,476	82,938
Cost Of Revenue [Member] | Product Recall Reserves [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Write down on specialized Fitbit Force tooling and manufacturing equipment			10,300
Production Related Impairments or Charges			$ 1,700
General and administrative [Member] | Product Recall Reserves [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Legal fees		2,900
Legal settlement costs (benefit)	$ (4,400)	$ 500

Balance Sheet Components - Accu

Balance Sheet Components - Accumulated Other Comprehensive Income (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2014	$ 37
Other comprehensive income (loss) before reclassifications	1,171
Amounts reclassified from AOCI	(517)
Other comprehensive income (loss)	654	$ 37
Balance at December 31, 2015	691	37
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, 2014	0
Other comprehensive income (loss) before reclassifications	1,276
Amounts reclassified from AOCI	(525)
Other comprehensive income (loss)	751
Balance at December 31, 2015	751	0
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2014	37
Other comprehensive income (loss) before reclassifications	(42)
Amounts reclassified from AOCI	0
Other comprehensive income (loss)	(42)
Balance at December 31, 2015	(5)	37
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance at December 31, 2014	0
Other comprehensive income (loss) before reclassifications	(63)
Amounts reclassified from AOCI	8
Other comprehensive income (loss)	(55)
Balance at December 31, 2015	$ (55)	$ 0

Long-Term Debt (Details)

Long-Term Debt (Details)	1 Months Ended			12 Months Ended
	Jan. 31, 2015USD ($)	Oct. 31, 2014USD ($)	Aug. 31, 2014USD ($)	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)	Aug. 31, 2012USD ($)
Line of Credit Facility [Line Items]
Interest expense				$ 1,000,000	$ 2,200,000	$ 1,100,000
Line of Credit [Member] | 2012 Financing Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity					$ 26,000,000
Line of Credit [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity			$ 180,000,000
Credit facility, amount outstanding				125,000,000
Credit facility, minimal stated interest rate			3.25%
Credit facility, minimum fixed charge coverage ratio			1
Credit facility, maximum leverage ratio			3
Credit facility, minimum leverage ratio			2
Credit facility, minimum liquidity level			$ 15,000,000
Repayment of line of credit	$ 125,000,000
Line of Credit [Member] | 2014 Credit Facility [Member] | Federal Funds Effective Rate [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate			0.50%
Line of Credit [Member] | 2014 Credit Facility [Member] | Eurodollar [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate			1.00%
Line of Credit [Member] | 2014 Credit Facility [Member] | Commitment Fee, Scenario One [Member]
Line of Credit Facility [Line Items]
Credit facility, commitment fee rate			0.25%
Line of Credit [Member] | 2014 Credit Facility [Member] | Commitment Fee, Scenario Two [Member]
Line of Credit Facility [Line Items]
Credit facility, commitment fee rate			0.35%
Line of Credit [Member] | 2014 Credit Facility [Member] | Commitment Fee, Scenario Three [Member]
Line of Credit Facility [Line Items]
Credit facility, commitment fee rate			0.45%
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				15
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%
Revolving Credit Facility [Member] | 2012 Financing Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity							$ 14,000,000
Revolving Credit Facility [Member] | 2014 Credit Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, effective interest rate				4.25%	425.00%
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%
Credit facility, amount outstanding				$ 8,000,000
Credit facility, maximum stated interest rate		3.50%
Credit facility, maximum leverage ratio		3
Credit facility, minimum leverage ratio		2
Repayment of line of credit				$ 8,000,000
Revolving Credit Facility [Member] | 2014 Revolving Credit And Guarantee 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] | 2014 Revolving Credit And Guarantee Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate		1.00%
Revolving Credit Facility [Member] | 2014 Revolving Credit And Guarantee Agreement [Member] | Commitment Fee, Scenario One [Member]
Line of Credit Facility [Line Items]
Credit facility, commitment fee rate		0.375%
Revolving Credit Facility [Member] | 2014 Revolving Credit And Guarantee Agreement [Member] | Commitment Fee, Scenario Two [Member]
Line of Credit Facility [Line Items]
Credit facility, commitment fee rate		0.50%
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] | London Interbank Offered Rate (LIBOR) [Member]
Line of Credit Facility [Line Items]
Credit facility, basis spread on variable rate				1.00%
Senior Term Loan [Member] | 2012 Financing Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity							3,000,000
Mezzanine Term Loan [Member] | 2012 Financing Facility [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity							$ 9,000,000
Letter of Credit [Member]
Line of Credit Facility [Line Items]
Credit facility, amount outstanding				$ 17,100,000	$ 2,900,000
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
Letter of Credit [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity				50,000,000
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
Swing Line Loan [Member] | 2015 Credit Agreement [Member]
Line of Credit Facility [Line Items]
Credit facility, borrowing capacity				$ 25,000,000

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) $ in Millions	Jul. 08, 2015patent	Jul. 03, 2015patent	Jun. 10, 2015patent	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Rent expense | $				$ 8.4	$ 4.1	$ 0.9
Purchase Commitment [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Purchase commitment | $				$ 452.4
Pending Litigation [Member] | Jawbone Patent Litigation [Member]
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Patents allegedly infringed | patent	6		3
Additional patents allegedly infringed | patent		3

Commitments and Contingencies63

Commitments and Contingencies - Future Minimum Payments (Details) $ in Thousands	Dec. 31, 2015USD ($)
Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract]
2,016	$ 16,843
2,017	20,825
2,018	19,835
2,019	18,789
2,020	15,312
Thereafter	52,020
Total	$ 143,624

Redeemable Convertible Prefer64

Redeemable Convertible Preferred Stock and Warrants - Preferred Shares (Details) - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Temporary Equity [Line Items]
Preferred stock authorized (in shares)	0	144,528,912
Preferred stock outstanding (in shares)	0	139,851,483
Preferred stock, net carrying value	$ 0	$ 67,814,000
Preferred stock, liquidation preference	$ 0	$ 66,619,000
Series A [Member]
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		10,200,000
Preferred stock outstanding (in shares)		10,200,000
Preferred stock, price (in dollars per share)		$ 0.04167
Preferred stock, net carrying value		$ 421,000
Preferred stock, liquidation preference		$ 425,000
Series A-1 [Member]
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		22,369,000
Preferred stock outstanding (in shares)		22,369,000
Preferred stock, price (in dollars per share)		$ 0.09164
Preferred stock, net carrying value		$ 2,000,000
Preferred stock, liquidation preference		$ 2,050,000
Series B [Member]
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		42,360,000
Preferred stock outstanding (in shares)		42,052,000
Preferred stock, price (in dollars per share)		$ 0.21580
Preferred stock, net carrying value		$ 10,533,000
Preferred stock, liquidation preference		$ 9,075,000
Series C [Member]
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		39,600,000
Preferred stock outstanding (in shares)		36,080,000
Preferred stock, price (in dollars per share)		$ 0.33452
Preferred stock, net carrying value		$ 12,049,000
Preferred stock, liquidation preference		$ 12,069,000
Series D [Member]
Temporary Equity [Line Items]
Preferred stock authorized (in shares)		30,000,000
Preferred stock outstanding (in shares)		29,150,000
Preferred stock, price (in dollars per share)		$ 1.47513
Preferred stock, net carrying value		$ 42,811,000
Preferred stock, liquidation preference		$ 43,000,000

Redeemable Convertible Prefer65

Redeemable Convertible Preferred Stock and Warrants - Warrants Issued and Outstanding (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)		1,955
Fair value of warrants	$ 0	$ 15,797
Series B [Member]
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)		278
Fair value of warrants		$ 2,351
Exercise price of warrants (in dollars per share)		$ 0.22
Series C Preferred Stock - April 2012 [Member]
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)		57
Fair value of warrants		$ 475
Exercise price of warrants (in dollars per share)		$ 0.33
Series C Preferred Stock - September 2012 - Group One [Member]
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)		1,215
Fair value of warrants		$ 9,728
Exercise price of warrants (in dollars per share)		$ 0.67
Series C Preferred Stock - September 2012 - Group Two [Member]
Class of Warrant or Right [Line Items]
Number of shares underlying warrants (in shares)		405
Fair value of warrants		$ 3,243
Exercise price of warrants (in dollars per share)		$ 0.67

Redeemable Convertible Prefer66

Redeemable Convertible Preferred Stock and Warrants - Fair Value Assumptions (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term	6 months
Volatility rate	81.30%
Risk-free interest rate	0.10%
Dividend yield	0.00%	0.00%	0.00%
Minimum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term		9 months 18 days	7 months 6 days
Volatility rate		46.70%	31.20%
Risk-free interest rate		0.10%	0.10%
Maximum [Member]
Fair Value Measurements, Recurring and Nonrecurring, Valuation Techniques [Line Items]
Expected term		1 year 3 months 18 days	6 years 10 months 24 days
Volatility rate		54.90%	62.70%
Risk-free interest rate		0.20%	2.50%

Redeemable Convertible Prefer67

Redeemable Convertible Preferred Stock and Warrants - Narrative (Details)	Jun. 22, 2015shares
Common Class B [Member]
Temporary Equity [Line Items]
Preferred stock, conversion	1
Shares issued in conversion of outstanding redeemable convertible preferred stock (in shares)	139,851,483
Series B [Member]
Temporary Equity [Line Items]
Shares issued (in shares)	274,992
Warrants exercised (in shares)	277,992
Warrants forfeited (in shares)	3,000
Series C [Member]
Temporary Equity [Line Items]
Shares issued (in shares)	1,210,591
Warrants exercised (in shares)	1,251,357
Warrants forfeited (in shares)	40,766

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	May. 31, 2015shares	Dec. 31, 2015USD ($)classvote$ / sharesshares	Dec. 31, 2014USD ($)$ / sharesshares	Dec. 31, 2013USD ($)$ / shares	Jun. 22, 2015class$ / shares
Class of Stock [Line Items]
Preferred stock, authorized (in shares)		10,000,000
Preferred stock, par value (in dollars per share) | $ / shares		$ 0.0001
Preferred stock, shares issued (in shares)		0
Preferred stock, shares outstanding (in shares)		0
Common stock issued (in shares)		0	40,875,583
Common stock outstanding (in shares)		0	40,875,583
Number of classes of stock | class		2			2
Common stock authorized (in shares)		0	230,400,000
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total grant date fair value of options that vested | $		$ 18,600	$ 1,700	$ 300
Weighted average grant date fair value (in dollars per share) | $ / shares		$ 10.67	$ 2.40	$ 0.52
Unrecognized compensation expense related to unvested options | $		$ 78,200
Total stock-based compensation expense | $		$ 41,024	$ 6,804	$ 620
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options, estimated weighted average period		2 years 11 months
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options, estimated weighted average period		3 years 6 months
Unrecognized compensation expense related to unvested options, net of estimated forfeitures | $		$ 96,600
Amended And Restated 2007 Stock Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Vesting percentage		25.00%
Requisite period		1 year
Expiration period		10 years
Maximum percentage of purchase price of fair value for employee purchase		100.00%
Amended And Restated 2007 Stock Plan [Member] | Non-statutory Employee Stock Option [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of purchase price of fair value for employee purchase		85.00%
2015 Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Expiration period		10 years
Maximum percentage of purchase price of fair value for employee purchase		100.00%
2015 Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Expiration period		10 years
Common Stock [Member] | FitStar [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation expense related to unvested options, estimated weighted average period		2 years 2 months
Unrecognized compensation expense related to unvested options, net of estimated forfeitures | $		$ 1,700
Minimum [Member] | Amended And Restated 2007 Stock Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		3 years
Maximum [Member] | Amended And Restated 2007 Stock Plan [Member] | Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period		4 years
Common Class A [Member]
Class of Stock [Line Items]
Common stock issued (in shares)		99,416,351	0
Common stock outstanding (in shares)		99,416,351	0
Common stock authorized (in shares)		600,000,000	0
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001
Common stock, votes per share | vote		1
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) | $ / shares		$ 29.59
Common Class A [Member] | 2015 Plan [Member] | Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock, annual increase based on shares outstanding, percent	5.00%
Common stock reserved for future issuance (in shares)		3,685,100
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
Common stock discount available to employees	15.00%
Common stock, fair value of market value of stock, available to employees, percent	85.00%
Share price (in dollars per share) | $ / shares					$ 20
Common Class B [Member]
Class of Stock [Line Items]
Common stock issued (in shares)		115,365,222	0
Common stock outstanding (in shares)		115,365,222	0
Common stock authorized (in shares)		350,000,000	0
Common stock, par value (in dollars per share) | $ / shares		$ 0.0001	$ 0.0001
Common stock, votes per share | vote		10

Stockholders' Equity - Stock Op

Stockholders' Equity - Stock Option Activity (Details) - 2007 And 2015 Equity Incentive Plan [Member] - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance, beginning of period (in shares)	43,998	23,404	20,947
Granted (in shares)	6,950	22,094	6,476
Exercised (in shares)	(5,397)	(735)	(3,283)
Canceled (in shares)	(1,189)	(765)	(736)
Balance, end of period (in shares)	44,362	43,998	23,404
Options exercisable (in shares)	20,763
Options vested and expected to vest (in shares)	43,502
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)	$ 1.72	$ 0.21	$ 0.06
Granted, weighted average exercise price (in dollars per share)	10.67	3.25	0.61
Exercised, weighted average exercise price (in dollars per share)	0.74	0.14	0.05
Canceled, weighted average exercise price (in dollars per share)	3.21	0.95	0.16
Balance, weighted average exercise price, end of period (in dollars per share)	3.20	$ 1.72	$ 0.21
Options exercisable, weighted average exercise price (in dollars per share)	0.99
Options vested and expected to vest, weighted average exercise price (in dollars per share)	$ 3.16
Options outstanding, aggregate intrinsic value, beginning of period	$ 207,863
Options canceled, aggregate intrinsic value	173,507	$ 3,001	$ 1,111
Options outstanding, aggregate intrinsic value, end of period	1,171,688	$ 207,863
Options exercisable, aggregate intrinsic value	593,810
Options vested and expected to vest, aggregate intrinsic value	$ 1,150,881

Stockholders' Equity - Restrict

Stockholders' Equity - Restricted Stock Unit Activity (Details) - Restricted Stock Units (RSUs) [Member] shares in Thousands	12 Months Ended
	Dec. 31, 2015$ / 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	0
Granted (in shares) | shares	3,326
Forfeited or canceled (in shares) | shares	(34)
Unvested balance—December 31, 2015 (in shares) | shares	3,292
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	$ 0
Granted (in dollars per share) | $ / shares	34.27
Forfeited or canceled (in dollars per share) | $ / shares	34.26
Unvested balance—December 31, 2015 (in dollars per share) | $ / shares	$ 34.27

Stockholders' Equity - Stock Co

Stockholders' Equity - Stock Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 41,024	$ 6,804	$ 620
Cost of revenue [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	4,739	890	37
Research and development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	18,251	2,350	288
Sales and marketing [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	7,419	1,295	204
General and administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Total stock-based compensation expense	$ 10,615	$ 2,269	$ 91

Stockholders' Equity - Valuatio

Stockholders' Equity - Valuation Assumptions (Details) - Stock Options [Member]	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years 3 months	6 years 3 months
Minimum volatility rate	52.10%	54.83%	60.57%
Maximum volatility rate	56.90%	60.94%	62.03%
Minimum risk-free interest rate	1.50%	1.73%	1.04%
Maximum risk-free interest rate	1.90%	2.04%	1.93%
Dividend yield rate	0.00%	0.00%	0.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term			6 years
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term			6 years 3 months

Income Taxes - Components of In

Income Taxes - Components of Income (Loss) Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
United States	$ 278,250	$ 150,137	$ (13,779)
Foreign	9,699	(10,364)	94
Income (loss) before income taxes	$ 287,949	$ 139,773	$ (13,685)

Income Taxes - Components of 74

Income Taxes - Components of Income Tax Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Current:
Federal	$ 140,396	$ 47,565	$ 31,176
State	13,307	2,319	6,736
Foreign	1,107	113	25
Total current	154,810	49,997	37,937
Deferred:
Federal	(33,421)	(39,339)	0
State	(8,941)	(2,651)	0
Foreign	(176)	(11)	0
Total deferred	(42,538)	(42,001)	0
Total income tax expense	$ 112,272	$ 7,996	$ 37,937

Income Taxes - Reconciliation o

Income Taxes - Reconciliation of Effective Tax to Statutory Federal Rate (Details)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Tax Disclosure [Abstract]
Tax at federal statutory rate	35.00%	35.00%	(35.00%)
State taxes, net of federal effect	1.50%	(0.20%)	32.00%
Foreign rate differential	(0.80%)	2.70%	(0.10%)
Tax credits	(2.00%)	(1.10%)	(9.60%)
Domestic production activities deduction	(3.30%)	(2.60%)	(12.70%)
Warrant fair value adjustment	6.90%	3.30%	8.60%
Effective Income Tax Rate Reconciliation, Nondeductible Expense, Share-based Compensation Cost, Percent	1.70%	0.00%	0.00%
Change in valuation allowance	0.00%	(32.00%)	292.60%
Other	0.00%	0.60%	1.40%
Effective tax rate	39.00%	5.70%	277.20%

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences for Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Net operating losses and credits	$ 5,225	$ 1,331
Fixed assets and intangible assets	1,227	2,436
Accruals and reserves	54,891	23,331
Fitbit Force recall reserve	1,910	8,159
Stock-based compensation	9,642	1,306
Other	10,566	5,438
Gross deferred tax assets	83,461	42,001
Debt issuance costs	(441)	0
Net deferred tax assets	$ 83,020	$ 42,001

Income Taxes - Reconciliation77

Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of year	$ 10,594	$ 7,991	$ 634
Reductions based on tax positions related to prior year	(18)	(418)	(87)
Additions based on tax positions related to current year	12,942	3,021	7,444
Balance at end of year	$ 23,518	$ 10,594	$ 7,991

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Tax Examination [Line Items]
Income tax expense	$ 112,272	$ 7,996	$ 37,937
Effective income tax rate	39.00%	5.70%	277.20%
Income tax benefit adjustment	$ 51,300	$ 51,300
Potential increase due to equity recognition	25,100
Federal operating loss carryforwards	5,800
Foreign net operating loss carryforwards	25,100
Unrecognized tax benefits	23,518	10,594	$ 7,991	$ 634
Unrecognized tax benefits, interest on income taxes expense	600	300
Undistributed Earnings of Foreign Subsidiaries	1,600
Domestic Tax Authority [Member]
Income Tax Examination [Line Items]
Deferred tax assets, research credit carryforwards	200
State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Income tax benefit adjustment		$ 6,400
California [Member]
Income Tax Examination [Line Items]
State net operating loss carryforwards	5,700
California Tax Authority [Member] | State and Local Jurisdiction [Member]
Income Tax Examination [Line Items]
Deferred tax assets, research credit carryforwards	$ 6,400

Related-Party Transactions (Det

Related-Party Transactions (Details) - SoftBank BB Corporation [Member] - Affiliated Entity [Member] - Distribution Rights Agreement [Member] - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Revenue from related parties	$ (1,700,000)	$ 17,600,000
Expenses from related parties		$ 100,000
Product sales from related parties	1,200,000
Sales returns from related parties	2,900,000
Additional refund paid to related parties	300,000
Amount due to related parties	0
Amounts due from related parties	$ 0

Net Income (Loss) per Share A80

Net Income (Loss) per Share Attributable to Common Stockholders (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Net income (loss)	$ 64,165	$ 45,834	$ 17,681	$ 47,997	$ 39,240	$ 68,912	$ 14,753	$ 8,872	$ 175,677	$ 131,777	$ (51,622)
Less: noncumulative dividends to preferred stockholders									(2,526)	(5,326)	0
Less: undistributed earnings to participating securities									(59,133)	(98,103)	0
Net income (loss) attributable to common stockholders—basic									114,018	28,348	(51,622)
Add: adjustments to undistributed earnings to participating securities									(8,821)	(10,175)	0
Net income (loss) attributable to common stockholders—diluted									$ 122,839	$ 38,523	$ (51,622)
Denominator:
Weighted-average shares of common stock— basic for Class A and Class B (in shares)									129,886	40,351	39,179
Effect of dilutive securities (in shares)									34,327	20,828	0
Weighted-average shares of common stock—diluted for Class A and Class B (in shares)									164,213	61,179	39,179
Net income (loss) per share attributable to common stockholders:
Basic (in dollars per share)	$ 0.30	$ 0.22	$ 0.09	$ 0.26	$ 0.21	$ 0.38	$ 0.07	$ 0.04	$ 0.88	$ 0.70	$ (1.32)
Diluted (in dollars per share)	$ 0.26	$ 0.19	$ 0.07	$ 0.22	$ 0.19	$ 0.34	$ 0.07	$ 0.04	$ 0.75	$ 0.63	$ (1.32)

Net Income (Loss) per Share A81

Net Income (Loss) per Share Attributable to Common Stockholders - Antidilutive Securities (Details) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share, amount	67,961	146,226	165,246
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	65,903	139,851	139,504
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	445	4,420	23,440
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	692	0	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	921	1,955	2,302

Significant Customer Informat82

Significant Customer Information and Other Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Concentration Risk [Line Items]
Revenue	$ 711,570	$ 409,262	$ 400,412	$ 336,754	$ 370,184	$ 152,862	$ 113,572	$ 108,815	$ 1,857,998	$ 745,433	$ 271,087
Geographic Concentration Risk [Member] | Non-US [Member]
Concentration Risk [Line Items]
Long-lived assets including property and equipment	$ 28,900				$ 20,000				$ 28,900	$ 20,000
Revenue [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									15.00%	13.00%
Revenue [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									14.00%	12.00%	14.00%
Revenue [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									14.00%	11.00%	14.00%
Revenue [Member] | Geographic Concentration Risk [Member]
Concentration Risk [Line Items]
Revenue									$ 1,857,998	$ 745,433	$ 271,087
Revenue [Member] | Geographic Concentration Risk [Member] | United States [Member]
Concentration Risk [Line Items]
Revenue									1,381,152	562,553	206,082
Revenue [Member] | Geographic Concentration Risk [Member] | Americas excluding United States [Member]
Concentration Risk [Line Items]
Revenue									92,252	38,576	9,094
Revenue [Member] | Geographic Concentration Risk [Member] | Europe, Middle East, and Africa [Member]
Concentration Risk [Line Items]
Revenue									208,767	60,699	25,041
Revenue [Member] | Geographic Concentration Risk [Member] | APAC [Member]
Concentration Risk [Line Items]
Revenue									$ 175,827	$ 83,605	$ 30,870
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer A [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									15.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer B [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									19.00%	17.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer C [Member]
Concentration Risk [Line Items]
Concentration risk, percentage									23.00%	14.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer D [Member]
Concentration Risk [Line Items]
Concentration risk, percentage										13.00%
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Customer E [Member]
Concentration Risk [Line Items]
Concentration risk, percentage										10.00%

Acquisition - Narrative (Detail

Acquisition - Narrative (Details) - USD ($)	Mar. 13, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Business Acquisition [Line Items]
Change in contingent consideration		$ (7,704,000)	$ 0	$ 0
FitStar, Inc [Member]
Business Acquisition [Line Items]
Total consideration	$ 32,500,000
Shares repurchased	24,949
Cash paid for acquisition	$ 11,500,000
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
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]
Amortization period	7 years
FitStar, Inc [Member] | Customer relationships [Member]
Business Acquisition [Line Items]
Amortization period	1 year 3 months
FitStar, Inc [Member] | Trademarks [Member]
Business Acquisition [Line Items]
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	24,948
Shares repurchased, amount	$ 4,200,000

Acquisition - Assets Acquired a

Acquisition - Assets Acquired and Liabilities Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Mar. 13, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 22,157		$ 0
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

Selected Unaudited Quarterly 85

Selected Unaudited Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Quarterly Financial Information Disclosure [Abstract]
Revenue	$ 711,570	$ 409,262	$ 400,412	$ 336,754	$ 370,184	$ 152,862	$ 113,572	$ 108,815	$ 1,857,998	$ 745,433	$ 271,087
Gross profit	348,299	196,013	187,542	169,209	170,894	83,605	58,389	44,769	901,063	357,657	60,251
Net income	$ 64,165	$ 45,834	$ 17,681	$ 47,997	$ 39,240	$ 68,912	$ 14,753	$ 8,872	$ 175,677	$ 131,777	$ (51,622)
Net income per share attributable to common stockholders—basic (in dollars per share)	$ 0.30	$ 0.22	$ 0.09	$ 0.26	$ 0.21	$ 0.38	$ 0.07	$ 0.04	$ 0.88	$ 0.70	$ (1.32)
Net income per share attributable to common stockholders—diluted (in dollars per share)	$ 0.26	$ 0.19	$ 0.07	$ 0.22	$ 0.19	$ 0.34	$ 0.07	$ 0.04	$ 0.75	$ 0.63	$ (1.32)