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Acquired SJB Assets and FDIC Loss Sharing Asset - Additional Information (Detail) - USD ($)
 3 Months Ended
Oct. 16, 2009
Mar. 31, 2016
Dec. 31, 2015
Business Combinations [Abstract]      
Acquisition date   Oct. 16, 2009  
After-tax gain included in earnings due to purchase method $ 12,300,000    
Remaining discount associated with SJB loans   $ 3,100,000  
Expected cash flows   $ 1,600,000  
Remaining average lives of respective pools loans   3 years  
Allowance for PCI loans losses   $ 0 $ 0