Segment and Geographic Information - Activity Related to Net Revenue and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Segment Reporting Information [Line Items]
Total net revenue	$ 2,305,487	$ 1,705,645	$ 6,593,567	$ 4,765,170
Adjusted EBITDA:	(144,184)	(76,405)	(316,385)	(161,174)
Less: reconciling items	(127,851)	(75,321)	(337,977)	(199,061)
Net loss	(272,035)	(151,726)	(654,362)	(360,235)
Depreciation and amortization	50,250	32,544	134,172	87,426
Equity-based compensation and related taxes	65,275	36,317	173,963	95,074
Interest expense, net	14,432	7,066	33,922	18,269
Other (income), net	(2,182)	(1,054)	(5,582)	(2,661)
Provision for income taxes	76	448	1,502	953
Less: reconciling items	127,851	75,321	337,977	199,061
U.S.
Segment Reporting Information [Line Items]
Total net revenue	1,966,654	1,473,245	5,624,870	4,086,173
Adjusted EBITDA:	(62,878)	(26,036)	(91,002)	(26,774)
International
Segment Reporting Information [Line Items]
Total net revenue	338,833	232,400	968,697	678,997
Adjusted EBITDA:	(81,306)	(50,369)	(225,383)	(134,400)
Direct Retail
Segment Reporting Information [Line Items]
Total net revenue	2,299,680	1,692,456	6,562,620	4,722,267
Direct Retail | U.S.
Segment Reporting Information [Line Items]
Total net revenue	1,960,847	1,460,056	5,593,923	4,043,270
Direct Retail | International
Segment Reporting Information [Line Items]
Total net revenue	338,833	232,400	968,697	678,997
Other
Segment Reporting Information [Line Items]
Total net revenue	5,807	13,189	30,947	42,903
Other | U.S.
Segment Reporting Information [Line Items]
Total net revenue	$ 5,807	$ 13,189	$ 30,947	$ 42,903