Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 38,494	$ 47,683
Less: Accumulated depreciation	(32,027)	(33,471)
Total property and equipment, net	6,467	14,212
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	13,486	17,537
IT Equipment [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	3,853	8,509
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	20,790	20,633
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	335	626
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Total property and equipment, gross	$ 30	$ 378