CONSOLIDATED AND CONDENSED STATEMENTS OF OPERATIONS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement [Abstract]
Net revenue	$ 1,655,256	$ 1,122,856	$ 3,059,525	$ 2,083,681
Cost of goods sold	1,270,249	853,390	2,350,694	1,577,332
Gross profit	385,007	269,466	708,831	506,349
Operating expenses:
Customer service and merchant fees	61,792	39,125	115,676	74,183
Advertising	177,582	124,241	339,228	242,506
Selling, operations, technology, general and administrative	240,972	143,652	452,335	283,418
Total operating expenses	480,346	307,018	907,239	600,107
Loss from operations	(95,339)	(37,552)	(198,408)	(93,758)
Interest expense, net	(5,796)	(1,550)	(11,203)	(1,849)
Other income, net	666	451	1,607	627
Loss before income taxes	(100,469)	(38,651)	(208,004)	(94,980)
Provision for income taxes	265	224	505	434
Net loss	$ (100,734)	$ (38,875)	$ (208,509)	$ (95,414)
Net loss per share, basic and diluted (in dollars per share)	$ (1.13)	$ (0.45)	$ (2.35)	$ (1.10)
Weighted average number of common stock outstanding used in computing per share amounts, basic and diluted (in shares)	89,158	86,714	88,814	86,374