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Loans Held for Investment and Allowance for Credit Losses on Loans - Additional Information (Detail) - USD ($) | 9 Months Ended | 12 Months Ended
--- | --- | ---
Sep. 30, 2025 | Sep. 30, 2024 | Dec. 31, 2024
Financing Receivable Recorded Investment [Line Items] |  |  |
Gains (losses) on sale of property held in other real estate owned | $ (40,000) | $ 1,300,000 |
Interest income recognized on nonaccrual loans | 0 | 0 |
Interest income that would have been recognized | 3,600,000 | $ 2,600,000 |
Balance of modifies loans | 6,000,000 |  | $ 14,800,000
Commercial Real Estate |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Other real estate | 31,100,000 |  | 28,100,000
Construction and Development Real Estate Loan |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Other real estate | 15,600,000 |  |
U.S. Federal Agencies [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Nonaccrual loans guaranteed by government agencies | $ 10,000,000 |  | $ 9,000,000
Parent Company [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Percentage of loans secured by real estate | 70.00% |  |
BancFirst [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Loan percentage | 83.00% |  |
Pegasus and Worthington [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Loan percentage | 17.00% |  |

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