Collaboration Agreements - Schedule of Collaboration Revenue Attributable to Up-Front and Milestone Payments (Detail) (Up-front cash payment arrangement [Member], USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue attributable to up-front and milestone payments	$ 4,232	$ 57,742	$ 41,163	$ 137,479
Astellas Pharma Inc [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue attributable to up-front and milestone payments	4,232	52,256	41,163	65,449
Pfizer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Total collaboration revenue attributable to up-front and milestone payments		$ 5,486		$ 72,030