Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 31,110	$ 27,516
Accumulated depreciation and amortization	(14,275)	(12,780)
Property and Equipment, net	16,835	14,736
Computer and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	12,296	11,631
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	10,122	8,437
Website and Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment	6,299	5,461
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,393	$ 1,987