Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 17,479	$ 8,762
Less: Accumulated depreciation and amortization	(1,397)	(1,011)
Property and equipment, net	16,082	7,751
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,739	4,370
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	715	408
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	498	285
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,055	1,856
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 7,472	$ 1,843