Collaboration Agreements (Collaboration Receivable) (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Schedule Of Accounts Receivable [Line Items]
Collaboration Receivables	$ 35,458	$ 12,545
Astellas [Member]
Schedule Of Accounts Receivable [Line Items]
Collaboration Receivables	35,458	10,554
Pfizer [Member]
Schedule Of Accounts Receivable [Line Items]
Collaboration Receivables		$ 1,991