Collaboration Agreements (Development And Commercialization Cost-Sharing Payments Receivable) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Development Milestone Payments [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	$ 14,375	$ 14,214	$ 29,817	$ 29,016
Development Milestone Payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	14,013	11,226	28,128	21,113
Development Milestone Payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Development cost-sharing payments	362	2,988	1,689	7,903
Commercial Milestone Payments [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	151	549	(661)	494
Commercial Milestone Payments [Member] | Astellas [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	146	526	(670)	458
Commercial Milestone Payments [Member] | Pfizer [Member]
Collaboration Agreements [Line Items]
Commercialization cost-sharing payments	$ 5	$ 23	$ 9	$ 36