Property and Equipment, Net - Schedule of Property and Equipment, Net (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 19,891	$ 15,396
Less: Accumulated depreciation and amortization	(3,567)	(2,134)
Property and equipment, net	16,324	13,262
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	11,959	9,057
Furniture and fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,944	2,648
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,606	3,166
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	244	244
Construction in progress [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 138	$ 281