Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 42,999	$ 41,305
Less: Accumulated depreciation and amortization	(6,910)	(5,180)
Property and equipment, net	36,089	36,125
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,460	10,711
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,335	1,335
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,025	1,010
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,830	27,807
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,349	$ 442