Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Cash Flows from Operating Activities
Net loss	$ (185,829)	$ (277,192)	$ (102,777)
Adjustments to reconcile net loss to net cash provided by operating activities:
Provision for doubtful accounts	56	7,893	339
Provision for excess and obsolete inventory	11,828	14,833	4,993
Depreciation	48,889	39,971	36,046
Amortization of intangible assets	7,926	5,722	2,087
Accelerated depreciation of property and equipment	7,731	5,250	19,805
Amortization of issuance costs and discount on debt	785	951	466
Stock-based compensation	97,009	91,581	79,432
Deferred income taxes	(2,548)	173,906	(100,434)
Impairment of equity investment	6,000	0	0
Other	(1,395)	216	(423)
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(8,036)	63,784	(8,701)
Inventories	(12,860)	92,129	(61,975)
Prepaid expenses and other assets	125,914	(113,111)	(37,876)
Fitbit force recall reserve	(445)	(789)	(3,869)
Accounts payable	35,207	(86,115)	45,654
Accrued liabilities and other liabilities	(11,978)	56,172	213,361
Deferred revenue	(5,622)	(7,472)	5,456
Income taxes payable	575	(3,488)	47,136
Net cash provided by operating activities	113,207	64,241	138,720
Cash Flows from Investing Activities
Purchase of property and equipment	(52,880)	(89,160)	(78,640)
Purchase of marketable securities	(353,948)	(597,933)	(638,055)
Sales of marketable securities	9,983	42,406	46,511
Maturities of marketable securities	433,594	622,525	315,774
Acquisitions, net of cash acquired	(19,253)	(556)	(38,256)
Equity investment	0	(6,000)	0
Net cash provided by (used in) investing activities	17,496	(28,718)	(392,666)
Cash Flows from Financing Activities
Repayment of debt	747	0	0
Payment of offering costs	0	0	(1,236)
Proceeds from issuance of common stock	21,470	19,011	25,969
Taxes paid related to net share settlement of restricted stock units	(19,436)	(14,376)	(4,939)
Net cash provided by financing activities	1,287	4,635	19,794
Net increase (decrease) in cash and cash equivalents	131,990	40,158	(234,152)
Effect of exchange rate changes on cash and cash equivalents	0	488	(374)
Cash and cash equivalents at beginning of period	341,966	301,320	535,846
Cash and cash equivalents at end of period	473,956	341,966	301,320
Supplemental Disclosure
Cash paid for interest	631	1,019	624
Cash paid (received) for income taxes, net of $72 million income tax refund in 2018	(69,868)	382	34,014
Supplemental Disclosure of Non-Cash Investing and Financing Activity
Purchase of property and equipment included in accounts payable and accrued liabilities	6,615	4,197	19,778
Property acquired under capital leases	$ 2,700	$ 0	$ 0