Collaboration Agreements - Deferred Revenue (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Deferred Revenue Arrangement [Line Items]
Deferred revenue, Current	$ 16,931	$ 33,862
Deferred revenue, Long-term	4,233	8,465
Astellas Pharma Inc [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue, Current	16,931	33,862
Deferred revenue, Long-term	4,233	8,465
Total	$ 21,164	$ 42,327