Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Cash Flows from Operating Activities
Net Income (Loss) Attributable to Parent	$ (320,711)	$ (185,829)	$ (277,192)
Adjustments to reconcile net loss to net cash provided by operating activities:
Provision for doubtful accounts	297	56	7,893
Provision for excess and obsolete inventory	6,011	11,828	14,833
Depreciation	54,139	48,889	39,971
Non-cash lease expense	19,170	0	0
Amortization of intangible assets	8,699	7,926	5,722
Accelerated depreciation of property and equipment	206	7,731	5,250
Amortization of issuance costs and discount on debt	0	785	951
Stock-based compensation	77,739	97,009	91,581
Deferred income taxes	384	(2,548)	173,906
Impairment of equity investment	0	6,000	0
Other	515	(1,395)	216
Changes in operating assets and liabilities, net of acquisitions:
Accounts receivable	(21,313)	(8,036)	63,784
Inventories	(18,471)	(12,860)	92,129
Prepaid expenses and other assets	15,141	125,914	(113,111)
Fitbit Force recall reserve	(1)	(445)	(789)
Accounts payable	(52,560)	35,207	(86,115)
Accrued liabilities and other liabilities	93,262	(11,978)	56,172
Increase (Decrease) in Lease Liabilities	(22,889)	0	0
Deferred revenue	4,006	(5,622)	(7,472)
Income taxes payable	(456)	575	(3,488)
Net cash provided by (used in) operating activities	(156,832)	113,207	64,241
Cash Flows from Investing Activities
Purchase of property and equipment	(36,531)	(52,880)	(89,160)
Purchase of marketable securities	(347,579)	(353,948)	(597,933)
Sales of marketable securities	9,124	9,983	42,406
Maturities of marketable securities	405,596	433,594	622,525
Acquisitions, net of cash acquired	(4,849)	(19,253)	(556)
Equity investment	0	0	(6,000)
Net cash provided by (used in) investing activities	25,761	17,496	(28,718)
Cash Flows from Financing Activities
Repayment of debt	(550)	(747)	0
Finance Lease, Principal Payments	(2,703)	0	0
Proceeds from issuance of common stock	13,018	21,470	19,011
Taxes paid related to net share settlement of restricted stock units	(18,171)	(19,436)	(14,376)
Net cash provided by (used in) financing activities	(8,406)	1,287	4,635
Net increase (decrease) in cash and cash equivalents	(139,477)	131,990	40,158
Effect of exchange rate changes on cash and cash equivalents	0	0	488
Cash and cash equivalents at beginning of period	473,956	341,966	301,320
Cash and cash equivalents at end of period	334,479	473,956	341,966
Supplemental Disclosure
Cash paid for interest	669	631	1,019
Cash paid (received) for income taxes, net of $72 million income tax refund in 2018	(4,181)	(69,868)	382
Supplemental Disclosure of Non-Cash Investing and Financing Activity
Purchase of property and equipment included in accounts payable and accrued liabilities	5,720	6,615	4,197
Property acquired under capital leases	0	2,700	0
Contingent consideration related to acquisitions	$ 1,889	$ 0	$ 0