Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Oct. 01, 2016
Cash Flows from Operating Activities
Net income (loss)	$ (231,722)	$ 43,496
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Provision for doubtful accounts	7,805	0
Provision for inventory obsolescence	13,395	1,014
Depreciation	28,338	23,883
Write-off of property and equipment	5,250	762
Amortization of intangible assets	4,134	1,578
Stock-based compensation	67,256	58,175
Deferred income taxes	132,815	(27,794)
Other	1,301	(323)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	208,899	7,756
Inventories	79,448	(50,883)
Prepaid expenses and other assets	(125,504)	(38,788)
Fitbit Force recall reserve	(668)	(3,628)
Accounts payable	(122,160)	(13,125)
Accrued liabilities and other liabilities	(48,201)	43,285
Deferred revenue	(9,846)	554
Income taxes payable	(1,822)	19,756
Net cash provided by operating activities	8,718	65,718
Cash Flows from Investing Activities
Purchase of property and equipment	(58,199)	(66,798)
Purchases of marketable securities	(494,540)	(552,752)
Sales of marketable securities	19,806	45,011
Maturities of marketable securities	500,576	249,269
Acquisitions, net of cash acquired	(556)	(5,600)
Net cash used in investing activities	(32,913)	(330,870)
Cash Flows from Financing Activities
Payments of offering costs	0	(1,236)
Proceeds from issuance of common stock	13,893	18,316
Taxes paid related to net share settlement of restricted stock units	(10,804)	(3,228)
Net cash provided by financing activities	3,089	13,852
Net decrease in cash and cash equivalents	(21,106)	(251,300)
Effect of exchange rate on cash and cash equivalents	467	(326)
Cash and cash equivalents at beginning of period	301,320	535,846
Cash and cash equivalents at end of period	$ 280,681	$ 284,220