Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 650	$ 228
Less: accumulated depreciation	(85)	(14)
Total property and equipment, net	565	214
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	185	56
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	144	9
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	241	$ 163
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 80