Balance Sheet Components - Summary of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 450	$ 228
Less: accumulated depreciation	(53)	(14)
Total property and equipment, net	397	214
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	140	56
Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11	9
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	224	$ 163
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 75