Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jul. 01, 2017	Jul. 02, 2016
Cash Flows from Operating Activities
Net income (loss)	$ (118,319)	$ 17,376
Adjustments to reconcile net income (loss) to net cash provided by operating activities:
Provision for inventory obsolescence	8,409	665
Depreciation	19,199	13,121
Write-off of property and equipment	5,250	649
Amortization of intangible assets	2,753	1,066
Stock-based compensation	44,459	38,170
Deferred income taxes	16,137	(36,452)
Other	1,428	(700)
Changes in operating assets and liabilities:
Accounts receivable	261,165	91,537
Inventories	81,486	(13,351)
Prepaid expenses and other assets	(50,324)	(16,085)
Fitbit Force recall reserve	(500)	(2,974)
Accounts payable	(216,959)	(39,425)
Accrued liabilities and other liabilities	(43,963)	54,000
Deferred revenue	(5,477)	1,973
Income taxes payable	(1,516)	14,857
Net cash provided by operating activities	3,228	124,427
Cash Flows from Investing Activities
Purchase of property and equipment	(39,817)	(36,745)
Purchases of marketable securities	(317,678)	(392,738)
Sales of marketable securities	13,806	38,814
Maturities of marketable securities	351,144	140,262
Acquisitions, net of cash acquired	0	(5,600)
Net cash provided by (used in) investing activities	7,455	(256,007)
Cash Flows from Financing Activities
Payments of offering costs	0	(1,236)
Proceeds from issuance of common stock	11,407	14,467
Taxes paid related to net share settlement of restricted stock units	(5,234)	(1,107)
Cash and cash equivalents at end of period	6,173	12,124
Net increase (decrease) in cash and cash equivalents	16,856	(119,456)
Effect of exchange rate on cash and cash equivalents	532	(248)
Cash and cash equivalents at beginning of period	301,320	535,846
Cash and cash equivalents at end of period	$ 318,708	$ 416,142