Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 73,426	$ 44,944
Accumulated depreciation and amortization	(25,024)	(19,680)
Property and Equipment, net	48,402	25,264
Computer and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	19,981	16,056
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	39,293	18,396
Website and Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment	6,507	6,423
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Total property and equipment	$ 7,645	$ 4,069