Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Property Plant And Equipment [Line Items]
Total property and equipment	$ 53,167	$ 44,944
Accumulated depreciation and amortization	(22,390)	(19,680)
Property and Equipment, net	30,777	25,264
Computer and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	17,093	16,056
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	25,544	18,396
Website and Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment	6,423	6,423
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Total property and equipment	$ 4,107	$ 4,069