Balance Sheet Components - Summary of Property and Equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment	$ 6,801	$ 5,949
Less: Accumulated depreciation	(4,168)	(3,191)
Property and equipment, net	2,633	2,758
Scientific Equipment
Property Plant And Equipment [Line Items]
Property and equipment	5,531	4,858
Furniture and Equipment
Property Plant And Equipment [Line Items]
Property and equipment	682	546
Capitalized Software
Property Plant And Equipment [Line Items]
Property and equipment	280	237
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment	$ 308	$ 308