Estimated Useful Lives of Property and Equipment (Detail)	6 Months Ended
	Jun. 30, 2012
Laboratory equipment | Minimum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	5 years
Laboratory equipment | Maximum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	7 years
Office furniture and equipment | Minimum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	5 years
Office furniture and equipment | Maximum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	7 years
Leasehold improvements
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	Shorter of the useful life (5 to 7 years) or the lease term
Leasehold improvements | Minimum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	5 years
Leasehold improvements | Maximum
Property Plant and Equipment Estimated Useful Lives [Line Items]
Estimated useful lives	7 years