Commitments and Contingencies - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013
Commitments And Contingencies [Line Items]
Operating lease office space, in square feet	127,000
Lease expiry period	June 2019
License and research agreement fee	$ 12,000,000
Coverage under its relevant insurance policies	350,000
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 Sublicensing Income	10.00%
Royalty percentage on sales	4.00%
Sales milestone payments [Member] | Astellas Pharma Inc. [Member]
Commitments And Contingencies [Line Items]
Percentage of Sublicensing Income	10.00%
Milestone payments eligible to earn	320,000,000
Milestone payments earned	25,000,000
Accrued payment to licensor		2,500,000
Fifth Amendment To Lease Agreement [Member]
Commitments And Contingencies [Line Items]
Operating lease office space, in square feet	29,000
Tenant improvement allowance	900,000
Outstanding letters of credit collateralized by restricted cash	2,100,000
Minimum lease payments over the lease term	9,600,000
Collateralized letters of credit [Member]
Commitments And Contingencies [Line Items]
Outstanding letters of credit collateralized by restricted cash	$ 12,000,000	$ 9,900,000