Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 21,584	$ 15,396
Less: Accumulated depreciation and amortization	(4,487)	(2,134)
Property and equipment, net	17,097	13,262
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,976	9,057
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,981	2,648
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,933	3,166
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	991	281
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 703	$ 244