Segment and Geographic Information - Activity Related to Net Revenue and Adjusted EBITDA (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Segment Reporting Information [Line Items]
Total net revenue	$ 1,655,256	$ 1,122,856	$ 3,059,525	$ 2,083,681
Adjusted EBITDA:	(34,809)	(2,246)	(84,769)	(23,142)
Less: reconciling items	65,925	36,629	123,740	72,272
Net loss	(100,734)	(38,875)	(208,509)	(95,414)
Depreciation and amortization	28,920	19,323	54,882	39,675
Equity based compensation and related taxes	31,610	15,983	58,757	30,941
Interest expense, net	5,796	1,550	11,203	1,849
Other (income), net	(666)	(451)	(1,607)	(627)
Provision for income taxes	265	224	505	434
Total reconciling items	65,925	36,629	123,740	72,272
U.S.
Segment Reporting Information [Line Items]
Total net revenue	1,411,344	997,068	2,612,928	1,855,097
Adjusted EBITDA:	7,200	20,425	(738)	24,153
International
Segment Reporting Information [Line Items]
Total net revenue	243,912	125,788	446,597	228,584
Adjusted EBITDA:	(42,009)	(22,671)	(84,031)	(47,295)
Direct Retail
Segment Reporting Information [Line Items]
Total net revenue	1,640,921	1,102,461	3,029,811	2,042,813
Direct Retail | U.S.
Segment Reporting Information [Line Items]
Total net revenue	1,397,009	976,673	2,583,214	1,814,229
Direct Retail | International
Segment Reporting Information [Line Items]
Total net revenue	243,912	125,788	446,597	228,584
Other
Segment Reporting Information [Line Items]
Total net revenue	14,335	20,395	29,714	40,868
Other | U.S.
Segment Reporting Information [Line Items]
Total net revenue	$ 14,335	$ 20,395	$ 29,714	$ 40,868