Commitments And Contingencies - Additional Information (Detail) (USD $)	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Commitments And Contingencies [Line Items]
Restricted cash, long-term assets	$ 8,843,000	$ 8,843,000
Percentage of sales milestone payments	10.00%
Coverage under its relevant insurance policies	350,000
Letter of credit [Member]
Commitments And Contingencies [Line Items]
Restricted cash, current	300,000	300,000
Restricted cash, long-term assets	8,900,000	8,900,000
Collateralized letter of credit [Member]
Commitments And Contingencies [Line Items]
Outstanding letters of credit collateralized by restricted cash	9,200,000	9,200,000
Sales milestone payments [Member]
Commitments And Contingencies [Line Items]
Milestone payments eligible to earn	320,000,000
Sales milestone payments [Member] | Astellas [Member]
Commitments And Contingencies [Line Items]
Percentage of sales milestone payments	10.00%
Maximum eligible future sales milestone payments under collaboration arrangement	320,000,000
Development milestone payments [Member]
Commitments And Contingencies [Line Items]
Aggregate milestone payments upon achievement of certain development and regulatory milestone events	2,800,000
Percentage of development milestone payment	10.00%
Royalty percentage on sales	4.00%
Milestone payments eligible to earn	$ 277,000,000