Property and Equipment - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 11,967	$ 2,518
Less: accumulated depreciation and amortization	(646)	(262)
Property and equipment, net	11,321	2,256
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,313	1,362
Computer Equipment and Software
Property Plant And Equipment [Line Items]
Property and equipment, gross	516	282
Office Equipment and Furniture
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,020	377
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,795	334
Construction in progress
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 2,323	$ 163