Balance Sheet Components - Components of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 9,286	$ 6,304
Less: accumulated depreciation and amortization	(3,065)	(1,651)
Total property and equipment, net	6,221	4,653
Laboratory and Manufacturing Equipment
Property Plant And Equipment [Line Items]
Total property and equipment, gross	1,994	1,509
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	1,015	736
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Total property and equipment, gross	953	657
Leasehold Improvements
Property Plant And Equipment [Line Items]
Total property and equipment, gross	726	502
Internal-Use Software
Property Plant And Equipment [Line Items]
Total property and equipment, gross	$ 4,598	$ 2,900