Significant Accounting Policies - Schedule of Estimated Useful Lives of Property and Equipment (Detail)	3 Months Ended
	Mar. 31, 2015
Laboratory equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	5 years
Computer equipment and software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	3 years
Leasehold improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	Shorter of asset's useful life or remaining term of lease
Build-to-suit property [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, estimated useful lives	10 years