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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, 2023 | Sep. 30, 2022 | Dec. 31, 2022
Financing Receivable Recorded Investment [Line Items] |  |  |
Gains (losses) on sale of property held in other real estate owned | $ 342,000 | $ 4,000,000 |
Interest income recognized on nonaccrual loans | 0 | 0 |
Nonaccrual loans with no related allowance for credit losses | 0 |  | $ 0
Balance of modifies loans | 8,400,000 |  |
Interest income that would have been recognized | 1,100,000 | $ 992,000 |
U.S. Federal Agencies [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Nonaccrual loans guaranteed by government agencies | 5,700,000 |  | 4,700,000
Other Real Estate Owned [Member] | Commercial Real Estate |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Other real estate | $ 32,700,000 |  | $ 29,400,000
Parent Company [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Percentage of loans secured by real estate | 69.00% |  |
BancFirst [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Loan percentage | 85.00% |  |
Pegasus and Worthington [Member] |  |  |
Financing Receivable Recorded Investment [Line Items] |  |  |
Loan percentage | 15.00% |  |

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- Definition Amount of interest income on financing receivable on nonaccrual status. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 16 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-16 + Details
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- Definition Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 326 -SubTopic 20 -Name Accounting Standards Codification -Section 50 -Paragraph 16 -Subparagraph (d) -Publisher FASB -URI https://asc.fasb.org//1943274/2147479319/326-20-50-16 + Details
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