| Off-Balance Sheet Commitments - Distribution of Undisbursed Loan Commitments (Detail) - USD ($) $ in Thousands | Mar. 31, 2020 | Dec. 31, 2019 | 
|---|---|---|
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | $ 416,982 | $ 413,792 | 
| Commitments to extend credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | 375,233 | 371,287 | 
| Standby letters of credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | 32,108 | 31,372 | 
| Commercial letters of credit | ||
| Loss Contingencies [Line Items] | ||
| Total undisbursed loan commitments | $ 9,642 | $ 11,133 | 
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- Definition Undisbursed loan commitments. No definition available. 
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