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
Dec. 31, 2018
Dec. 31, 2017
Loss Contingencies [Line Items]    
Total undisbursed loan commitments $ 371,448 $ 347,236
Commitments to extend credit    
Loss Contingencies [Line Items]    
Total undisbursed loan commitments 325,100 318,634
Standby letters of credit    
Loss Contingencies [Line Items]    
Total undisbursed loan commitments 32,500 19,294
Commercial letters of credit    
Loss Contingencies [Line Items]    
Total undisbursed loan commitments $ 13,848 $ 9,308