Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,859	$ 5,086
Less: Accumulated depreciation	(2,216)	(1,073)
Property and equipment, net	5,643	4,013
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,148	1,090
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,002	1,029
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 4,709	$ 2,967