Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2018	Jul. 01, 2017
Cash Flows from Operating Activities
Net loss	$ (199,145)	$ (118,319)
Adjustments to reconcile net loss to net cash (used in) provided by operating activities:
Provision for inventory obsolescence	8,014	8,409
Depreciation	23,572
Depreciation and amortization expense	23,600	19,199
Write-off of property and equipment	7,485	5,250
Amortization of intangible assets	3,805	2,753
Stock-based compensation	49,498	44,459
Deferred income taxes	(1,299)	16,137
Other	(419)	1,428
Changes in operating assets and liabilities, net of acquisition:
Accounts receivable	164,195	261,165
Inventories	(24,217)	81,486
Prepaid expenses and other assets	37,624	(50,324)
Fitbit Force recall reserve	(291)	(500)
Accounts payable	(64,184)	(216,959)
Accrued liabilities and other liabilities	(74,033)	(43,963)
Deferred revenue	(9,623)	(5,477)
Income taxes payable	21,801	(1,516)
Net cash (used in) provided by operating activities	(57,217)	3,228
Cash Flows from Investing Activities
Purchase of property and equipment	(28,524)	(39,817)
Purchases of marketable securities	(224,812)	(317,678)
Sales of marketable securities	73,770	13,806
Maturities of marketable securities	236,575	351,144
Acquisition, net of cash acquired	(13,646)	0
Net cash provided by investing activities	43,363	7,455
Cash Flows from Financing Activities
Repayment of debt	(747)	0
Proceeds from issuance of common stock	10,738	11,407
Taxes paid related to net share settlement of restricted stock units	(9,987)	(5,234)
Net cash provided by financing activities	4	6,173
Net (decrease) increase in cash and cash equivalents	(13,850)	16,856
Effect of exchange rate on cash and cash equivalents	0	532
Cash and cash equivalents at beginning of period	341,966	301,320
Cash and cash equivalents at end of period	$ 328,116	$ 318,708