Collaboration Agreements - Development and Commercialization Cost-Sharing Payments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Development cost-sharing payments [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	$ 11,309	$ 14,375	$ 18,547	$ 29,817
Development cost-sharing payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	11,309	14,013	18,547	28,128
Development cost-sharing payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments		362		1,689
Commercial cost sharing-payments [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(3,791)	151	(8,576)	(661)
Commercial cost sharing-payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(3,791)	146	(8,576)	(670)
Commercial cost sharing-payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments		$ 5		$ 9