Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 35,318	$ 32,876
Less accumulated depreciation and amortization	(8,591)	(7,992)
Property and equipment, net	26,727	24,884
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	825	752
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	7,319	6,291
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	678	678
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	26,263	1,602
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 233	$ 23,553