Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 28,818	$ 5,643
Less: accumulated depreciation and amortization	(2,887)	(1,657)
Property and equipment, net	25,931	3,986
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,051	3,011
Computer and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,501	959
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,211	306
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	15,753	669
Construction in Progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 6,302	$ 698