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New Accounting Standards - Additional Information (Detail) - USD ($)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2015
Oct. 02, 2015
New Accounting Pronouncement, Early Adoption [Line Items]      
Deferred debt issuance costs   $ 1,500,000  
Long-term borrowings $ 541,443,000 $ 641,480,000  
Debt issuance costs $ 0    
Subordinated Notes [Member]      
New Accounting Pronouncement, Early Adoption [Line Items]      
Long-term borrowings     $ 100,000,000