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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
Commitments And Contingencies Disclosure [Abstract]      
Rent expenses $ 0.7us-gaap_LeaseAndRentalExpense $ 0.7us-gaap_LeaseAndRentalExpense $ 0.6us-gaap_LeaseAndRentalExpense
Lease expiration date Jan. 31, 2018