Financial Statement Components - Components of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 103,376	$ 78,581
Less: accumulated depreciation and amortization	(60,078)	(46,587)
Property and equipment, net	43,298	31,994
Computer hardware and software
Property Plant And Equipment [Line Items]
Property and equipment, gross	74,555	61,546
Internal-use software development costs
Property Plant And Equipment [Line Items]
Property and equipment, gross	18,217	9,931
Furniture and fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,293	4,508
Leasehold improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 4,311	$ 2,596