Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Statement [Abstract]
Net revenue	$ 6,779,174	$ 4,720,895	$ 3,380,360
Cost of goods sold	5,192,451	3,602,072	2,572,549
Gross profit	1,586,723	1,118,823	807,811
Operating expenses:
Customer service and merchant fees	260,046	169,516	127,883
Advertising	774,189	549,959	409,125
Selling, operations, technology, general and administrative	1,025,767	634,801	467,020
Total operating expenses	2,060,002	1,354,276	1,004,028
Loss from operations	(473,279)	(235,453)	(196,217)
Interest (expense) income, net	(28,560)	(9,433)	694
Other (expense) income, net	(204)	758	1,756
Loss before income taxes	(502,043)	(244,128)	(193,767)
Provision for income taxes	2,037	486	608
Net loss	$ (504,080)	$ (244,614)	$ (194,375)
Net loss per share, basic and diluted (in dollars per share)	$ (5.63)	$ (2.81)	$ (2.29)
Weighted average number of common stock outstanding used in computing per share amounts, basic and diluted (in shares)	89,472	86,983	84,977