Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 74,430	$ 50,856
Less: Accumulated depreciation	(16,288)	(9,695)
Total	58,142	41,161
Build-to-suit property [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	18,371	19,544
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	19,074	15,051
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	16,083	9,499
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	5,714	4,667
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	14,440	1,360
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 748	$ 735