Collaboration Agreements (Collaboration Revenue Attributable To Up-Front And Milestone Payments) (Detail) (Up-Front And Milestone Payments [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Collaboration Agreements [Line Items]
Total collaboration revenue attributable to up-front and milestone payments	$ 57,742	$ 14,940	$ 137,479	$ 45,448
Astellas [Member]
Collaboration Agreements [Line Items]
Total collaboration revenue attributable to up-front and milestone payments	52,256	5,936	65,449	18,436
Pfizer [Member]
Collaboration Agreements [Line Items]
Total collaboration revenue attributable to up-front and milestone payments	$ 5,486	$ 9,004	$ 72,030	$ 27,012