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Commitments, Off Balance Sheets Risk and Contingencies - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
Commitments and Contingencies Disclosure [Abstract]    
Cash on hand or deposit with Federal Reserve Bank $ 1,800,000  
Commitments to make loans 808,300,000 $ 468,800,000
Commitments under outstanding standby letters of credit 1,000,000 $ 3,600,000
Anticipated losses from unused commitments $ 0