Property and Equipment - Property and Equipment and Related Accumulated Depreciation and Amortization (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Property, Plant and Equipment [Line Items]
Total cost	$ 116,586	$ 97,485
Less: accumulated depreciation and amortization	(65,808)	(56,366)
Total property and equipment, net	50,778	41,119
Lab Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	37,867	36,533
Computer Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	12,285	11,808
Software [Member]
Property, Plant and Equipment [Line Items]
Total cost	13,013	10,694
Furniture and Office Equipment [Member]
Property, Plant and Equipment [Line Items]
Total cost	5,442	3,959
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Total cost	37,765	26,968
Construction in Progress [Member]
Property, Plant and Equipment [Line Items]
Total cost	$ 10,214	$ 7,523