Commitments And Contingencies - Additional Information (Detail) (USD $)	6 Months Ended						1 Months Ended	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Letter of credit [Member]	Dec. 31, 2012 Letter of credit [Member]	Jun. 30, 2013 Collateralized letter of credit [Member]	Dec. 31, 2012 Collateralized letter of credit [Member]	Jun. 30, 2013 Fourth amendment to lease agreement [Member] sqft	Jun. 30, 2013 Fourth amendment to lease agreement [Member] Y sqft	Jun. 30, 2013 Non-cancellable lease agreement [Member] sqft	Jun. 30, 2013 Illinois [Member] Non-cancellable lease agreement [Member] sqft	Jun. 30, 2013 Sales milestone payments [Member]	Jun. 30, 2013 Sales milestone payments [Member] Astellas [Member]	Jun. 30, 2013 Development milestone payments [Member]
Commitments And Contingencies [Line Items]
Tenant improvement allowance								$ 400,000
Outstanding letters of credit collateralized by restricted cash							1,100,000	1,100,000
Increase in operating lease space							13,000
Operating lease space, in square feet							98,000	98,000		15,000
Lease expiry period								June 2019		December 2019
Optional lease extension term, in years								5
Operating lease space, in square feet									14,000
Lease expiry period									December 2015
Outstanding letters of credit collateralized by restricted cash					10,200,000	9,200,000
Restricted cash, current			300,000	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