Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 11,499	$ 7,859
Less: Accumulated depreciation	(3,136)	(2,216)
Property and equipment, net	8,363	5,643
Computer Hardware and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,427	2,148
Furniture and Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,774	1,002
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,298	$ 4,709