Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Commitments And Contingencies [Line Items]
Rent expense	$ 5,200,000	$ 6,000,000	$ 2,800,000
Restricted cash, current		343,000
Restricted cash, long-term assets	9,899,000	8,843,000
Coverage under its relevant insurance policies	350,000
Letter of credit [Member]
Commitments And Contingencies [Line Items]
Restricted cash, current		300,000
Restricted cash, long-term assets	9,900,000	8,800,000
Collateralized letters of credit [Member]
Commitments And Contingencies [Line Items]
Outstanding letters of credit collateralized by restricted cash	9,900,000	9,200,000
525 Market Street [Member]
Commitments And Contingencies [Line Items]
Operating lease space, in square feet	98,000
Lease expiry period	June 2019
Optional lease extension term, in years	5
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%
Sales milestone payments [Member]
Commitments And Contingencies [Line Items]
Milestone payments eligible to earn	320,000,000
Sales milestone payments [Member] | Astellas Pharma Inc. [Member]
Commitments And Contingencies [Line Items]
Milestone payments eligible to earn	320,000,000
Percentage of sales milestone payments	10.00%
Sales milestone payments under collaborative agreement	25,000,000
Accrued payment to sales milestone payments	$ 2,500,000
Illinois [Member] | Non-cancellable lease agreement [Member]
Commitments And Contingencies [Line Items]
Operating lease space, in square feet	15,000
Lease expiry period	December 2019
California [Member]
Commitments And Contingencies [Line Items]
Operating lease space, in square feet	52,000
Lease expiry period	July 2024
Optional lease extension term, in years	5