Commitments and Contingencies - Additional Information (Detail) (USD $)	9 Months Ended						6 Months Ended	9 Months Ended		6 Months Ended	9 Months Ended
	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Letter of credit [Member]	Dec. 31, 2012 Letter of credit [Member]	Sep. 30, 2013 Collateralized letter of credit [Member]	Dec. 31, 2012 Collateralized letter of credit [Member]	Jun. 30, 2013 Non-cancellable lease agreement [Member] sqft	Sep. 30, 2013 Fourth amendment to lease agreement [Member] Y sqft	Jun. 30, 2013 Fourth amendment to lease agreement [Member] sqft	Jun. 30, 2013 Illinois [Member] Non-cancellable lease agreement [Member] sqft	Sep. 30, 2013 Sales milestone payments [Member]	Sep. 30, 2013 Sales milestone payments [Member] Astellas Pharma Inc [Member]	Sep. 30, 2013 Development milestone payments [Member]
Commitments And Contingencies [Line Items]
Outstanding letters of credit collateralized by restricted cash								$ 1,100,000
Operating lease space, in square feet							14,000	98,000	13,000	15,000
Lease expiry period							December 2015	June 2019		December 2019
Optional lease extension term, in years								5
Outstanding letters of credit collateralized by restricted cash					9,900,000	9,200,000
Restricted cash, current				300,000
Restricted cash, long-term assets	9,899,000	8,843,000	9,900,000	8,800,000
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											320,000,000		257,000,000
Percentage of sales milestone payments												10.00%
Maximum eligible future sales milestone payments under collaboration arrangement												320,000,000
Coverage under its relevant insurance policies	$ 350,000