Collaboration Agreements - Development and Commercialization Cost-Sharing Payments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Development cost-sharing payments [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	$ 7,238	$ 15,442
Development cost-sharing payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	7,238	14,115
Development cost-sharing payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments		1,327
Commercial cost sharing-payments [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(4,785)	(812)
Commercial cost sharing-payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(4,785)	(816)
Commercial cost sharing-payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments		$ 4