Balance Sheet Components - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment	$ 8,791	$ 7,608
Less: Accumulated depreciation	(4,761)	(4,461)
Property and equipment, net	4,030	3,147
Scientific Equipment
Property Plant And Equipment [Line Items]
Property and equipment	7,102	5,935
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment	1,071	1,064
Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment	278	278
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment	$ 340	$ 331