Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 47,236	$ 22,398
Less: Accumulated depreciation	(7,556)	(5,363)
Total	39,680	17,035
Build-to-suit property [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	17,250
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	12,061	12,034
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	6,803	4,503
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	6,357	1,177
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,051	3,981
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 714	$ 703