Annual report pursuant to Section 13 and 15(d)

Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail)

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Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Loss Contingencies [Line Items]      
Total undisbursed loan commitments $ 413,792 $ 371,448  
Allowance for off-balance sheet items:      
Balance at beginning of period 1,439 1,296 $ 1,184
Provision charged to operating expense 958 143 112
Balance at end of period 2,397 1,439 $ 1,296
Commitments to extend credit      
Loss Contingencies [Line Items]      
Total undisbursed loan commitments 371,287 325,100  
Standby letters of credit      
Loss Contingencies [Line Items]      
Total undisbursed loan commitments 31,372 32,500  
Commercial letters of credit      
Loss Contingencies [Line Items]      
Total undisbursed loan commitments $ 11,133 $ 13,848