Collaboration Agreements - Development and Commercialization Cost-Sharing Payments (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Development cost-sharing payments [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	$ 13,070	$ 11,054	$ 31,617	$ 40,871
Development cost-sharing payments [Member] | Astellas Pharma Inc [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	13,070	11,003	31,617	39,131
Development cost-sharing payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments		51		1,740
Commercial cost sharing-payments [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(1,812)	(1,187)	(10,388)	(1,848)
Commercial cost sharing-payments [Member] | Astellas Pharma Inc [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	(1,812)	(1,187)	(10,388)	(1,857)
Commercial cost sharing-payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments				$ 9