Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Apr. 01, 2017
Cash Flows from Operating Activities
Net loss	$ (80,877)	$ (60,079)
Adjustments to reconcile net loss to net cash provided by operating activities:
Provision for inventory obsolescence	6,337	3,997
Depreciation	10,456	9,140
Write-off of property and equipment	7,259	0
Amortization of intangible assets	1,748	1,377
Stock-based compensation	23,641	22,493
Deferred income taxes	(1,799)	(5,005)
Other	(275)	(183)
Changes in operating assets and liabilities, net of acquisition:
Accounts receivable	191,982	282,917
Inventories	(27,307)	27,193
Prepaid expenses and other assets	39,610	(976)
Fitbit Force recall reserve	(132)	(295)
Accounts payable	(84,155)	(176,619)
Accrued liabilities and other liabilities	(70,147)	(52,173)
Deferred revenue	(6,010)	(3,000)
Income taxes payable	(173)	351
Net cash provided by operating activities	10,158	49,138
Cash Flows from Investing Activities
Purchase of property and equipment	(12,616)	(28,157)
Purchases of marketable securities	(141,404)	(129,661)
Sales of marketable securities	50,795	4,256
Maturities of marketable securities	148,041	178,028
Acquisition, net of cash acquired	(13,646)	0
Net cash provided by investing activities	31,170	24,466
Cash Flows from Financing Activities
Proceeds from issuance of common stock	992	2,581
Repayment of debt	(747)	0
Taxes paid related to net share settlement of restricted stock units	(5,179)	(3,127)
Net cash used in financing activities	(4,934)	(546)
Net increase in cash and cash equivalents	36,394	73,058
Effect of exchange rate on cash and cash equivalents	0	(99)
Cash and cash equivalents at beginning of period	341,966	301,320
Cash and cash equivalents at end of period	$ 378,360	$ 374,279