Collaboration Agreements - Development and Commercialization Cost-Sharing Payments (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Development cost-sharing payments [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost-sharing payments	$ 63,479	$ 46,594	$ 49,213
Development cost-sharing payments [Member] | Astellas Pharma Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost-sharing payments	63,479	46,594	47,473
Development cost-sharing payments [Member] | Pfizer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Development cost-sharing payments			1,740
Commercial cost sharing-payments [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercialization cost-sharing payments	(36,094)	(11,973)	(3,428)
Commercial cost sharing-payments [Member] | Astellas Pharma Inc. [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercialization cost-sharing payments	(36,094)	(11,973)	(3,437)
Commercial cost sharing-payments [Member] | Pfizer [Member]
Collaborative Arrangements and Non-collaborative Arrangement Transactions [Line Items]
Commercialization cost-sharing payments			$ 9