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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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