Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property and Equipment [Line Items]
Total property and equipment	$ 105,366	$ 65,380
Accumulated depreciation and amortization expenses	(31,738)	(14,458)
Total property and equipment, net	73,628	50,922
Depreciation expense	17,300	9,200	$ 2,600
Capitalized computer software, amortization	12,400	4,900	1,400
Computer hardware
Property and Equipment [Line Items]
Total property and equipment	10,421	5,667
Furniture and equipment
Property and Equipment [Line Items]
Total property and equipment	3,187	2,448
Internal-use software development costs
Property and Equipment [Line Items]
Total property and equipment	81,640	48,557
Total property and equipment, net	62,800	42,100
Capitalized computer software additions	33,100	27,100	$ 15,000
Leasehold improvements
Property and Equipment [Line Items]
Total property and equipment	$ 10,118	$ 8,708