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Commitments and Contingencies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Operating Leased Assets [Line Items]      
Lease agreement description During 2014, the Company exercised its 5-year renewal option on the manufacturing facility. The Company also entered into a new four-year lease for additional space in the manufacturing facility effective April 1, 2014. This lease also has an option to continue the lease for five years under the same terms.    
Deferred rent liability $ 2.7us-gaap_DeferredRentCredit $ 2.9us-gaap_DeferredRentCredit  
Rent expense $ 2.0us-gaap_OperatingLeasesRentExpenseNet $ 2.7us-gaap_OperatingLeasesRentExpenseNet $ 2.7us-gaap_OperatingLeasesRentExpenseNet
Office and Laboratory Space [Member] | Rockville, Maryland [Member]      
Operating Leased Assets [Line Items]      
Lease expiration date Mar. 31, 2018    
Amended lease expiration date Jan. 31, 2020    
Office and Laboratory Space [Member] | South San Francisco [Member]      
Operating Leased Assets [Line Items]      
Lease expiration date Feb. 28, 2018    
Manufacturing Space [Member]      
Operating Leased Assets [Line Items]      
Lease expiration date Dec. 31, 2014    
Lessee leasing arrangements, operating leases, renewal term 5 years    
Additional Manufacturing Space [Member]      
Operating Leased Assets [Line Items]      
Term of additional space lease 4 years    
Origination date for additional space in manufacturing facility Apr. 01, 2014