Balance Sheet Components - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,858	$ 2,076
Less: accumulated depreciation and amortization	(1,404)	(1,023)
Property and equipment, net	2,454	1,053
Lab Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,400	1,165
Computer and Office Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	755	520
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	170	87
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 533	$ 304