Property and Equipment - Property and Equipment and Related Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment [Line Items]
Total cost	$ 97,485	$ 84,570
Less: accumulated depreciation and amortization	(56,366)	(43,084)
Total property and equipment, net	41,119	41,486
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	36,533	34,727
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	11,808	11,534
Software [Member]
Property, Plant and Equipment [Line Items]
Total cost	10,694	5,429
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	3,959	3,638
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost	26,968	24,730
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 7,523	$ 4,512