Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail) - USD ($) $ in Thousands  | 
Mar. 31, 2021  | 
Dec. 31, 2020  | 
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| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | $ 580,861 | $ 555,616 | 
| Commitments to extend credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | 463,841 | 453,900 | 
| Standby letters of credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | 48,922 | 47,169 | 
| Commercial letters of credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | $ 68,098 | $ 54,547 | 
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- Definition Undisbursed loan commitments. No definition available. 
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