Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 57,005	$ 50,856
Less: Accumulated depreciation	(12,714)	(9,695)
Total	44,291	41,161
Build-to-suit property [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	17,656	19,544
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	15,027	15,051
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,012	9,499
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,576	4,667
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	7,999	1,360
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 735	$ 735