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Commitments, Off-Balance Sheet Risk and Contingencies - Additional Information (Detail) - USD ($)
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Commitments and Contingencies Disclosure [Abstract]    
Commitments to make loans $ 958,700,000 $ 873,800,000
Commitments under outstanding standby letters of credit 17,300,000 $ 4,800,000
Anticipated losses from unused commitments $ 0