Segment and Geographic Information - Net Revenues and Adjusted EBITDA (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total net revenue		$ 9,127,057	$ 6,779,174	$ 4,720,895
Adjusted EBITDA		(496,544)	(214,986)	(67,033)
Less: reconciling items		(488,040)	(289,094)	(177,581)
Net loss		(984,584)	(504,080)	(244,614)
Depreciation and amortization		192,419	123,542	87,020
Equity-based compensation and related taxes		240,978	136,415	72,626
Interest (expense), net		54,514	28,560	9,433
Other (income) expense, net		(2,881)	204	(758)
Provision for income taxes, net		3,010	2,037	486
Other		0	(1,664)	8,774
Total reconciling items		488,040	289,094	177,581
Selling, operations, technology, general and administrative		1,624,706	1,025,767	634,801
Leasehold improvements
Segment Reporting Information [Line Items]
Depreciation and amortization				800
Warehouse vacated
Segment Reporting Information [Line Items]
Other	$ 1,700			8,800
Selling, operations, technology, general and administrative				9,600
U.S.
Segment Reporting Information [Line Items]
Total net revenue		7,764,831	5,813,070	4,153,057
Adjusted EBITDA		(179,010)	(19,049)	35,888
International
Segment Reporting Information [Line Items]
Total net revenue		1,362,226	966,104	567,838
Adjusted EBITDA		$ (317,534)	$ (195,937)	$ (102,921)