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 loss	$ (984,584)	$ (504,080)	$ (244,614)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	192,419	123,542	87,020
Equity-based compensation	227,451	127,564	67,840
Amortization of discount and issuance costs on convertible notes	62,111	22,585	5,830
Other non-cash adjustments	(1,691)	(56)	1,198
Changes in operating assets and liabilities:
Accounts receivable	(49,187)	(12,792)	(18,172)
Inventories	(15,631)	(18,319)	(9,454)
Prepaid expenses and other current assets	(32,590)	(65,195)	(39,124)
Accounts payable and accrued expenses	330,325	285,064	104,184
Unearned revenue and other liabilities	75,888	134,705	81,354
Other assets	(1,329)	(8,157)	(2,428)
Net cash (used in) provided by operating activities	(196,818)	84,861	33,634
Cash flows from investing activities:
Purchase of short- and long-term investments	(553,858)	(99,002)	(54,551)
Sale and maturities of short-term investments	115,468	61,068	71,095
Purchase of property and equipment	(271,742)	(159,205)	(100,451)
Site and software development costs	(129,138)	(62,750)	(46,428)
Other investing activities, net	(15,567)	(398)	0
Net cash used in investing activities	(854,837)	(260,287)	(130,335)
Cash flows from financing activities:
Proceeds from issuance of convertible notes, net of issuance costs	935,146	562,047	420,449
Premiums paid for capped call confirmations	(145,728)	(93,438)	(44,160)
Taxes paid related to net share settlement of equity awards	(2,236)	(1,284)	(1,562)
Deferred financing costs	(791)	0	0
Net proceeds from exercise of stock options	113	138	244
Net cash provided by financing activities	786,504	467,463	374,971
Effect of exchange rate changes on cash and cash equivalents	(1,557)	(1,536)	850
Net (decrease) increase in cash and cash equivalents	(266,708)	290,501	279,120
Cash and cash equivalents:
Beginning of year	849,461	558,960	279,840
End of year	582,753	849,461	558,960
Supplemental Cash Flow Information:
Cash paid for interest on long-term debt	7,763	1,554	0
Cash paid for interest on finance lease obligations	0	9,058	0
Purchase of property and equipment included in accounts payable and accrued expenses and in other liabilities	41,181	15,383	8,533
Construction costs capitalized under finance lease obligations and other leases	$ 0	$ 125,796	$ 47,276