Balance Sheet Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Total property and equipment	$ 36,300	$ 27,516
Accumulated depreciation and amortization	(16,088)	(12,780)
Property and Equipment, net	20,212	14,736
Computer and Equipment
Property Plant And Equipment [Line Items]
Total property and equipment	13,508	11,631
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment	13,270	8,437
Website and Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment	6,925	5,461
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Total property and equipment	$ 2,597	$ 1,987