Amount transferred from loans held for investment net of unearned interest to loans held for sale.

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Collateral dependent loans financing receivable with related allowance interest income accrual method.

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Financing receivable modifications due to impact of CARES act.

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Nonaccrual loan amount guaranteed by government agencies.

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Pay check protection program loan held for investment.

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Paycheck protection program unamortized processing fees.

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Paycheck protection program unamortized processing fees recognized as interest income.

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Percentage of loans secured by real estate.

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Amount of credit loss expense (reversal of expense) for financing receivable from change in methodology.

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The net gain (loss) resulting from sales and other disposals of other real estate owned, increases (decreases) in the valuation allowance for foreclosed real estate, and write-downs of other real estate owned after acquisition or physical possession.

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Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

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Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period).

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Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

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Amount, before valuation allowance, of financing receivable classified as held-for-sale.

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Amount of credit loss expense (reversal of expense) for financing receivable.

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Loans Held for Investment and Allowance for Credit Losses on Loans - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 6,394,506,000	$ 5,662,143,000
Pay check protection program loan held for investment	652,700,000
Paycheck protection program unamortized processing fees	14,500,000
Paycheck protection program unamortized processing fees recognized as interest income	15,600,000
Gains on sale of property held in other real estate owned	2,400,000	1,400,000	$ 23,500
Interest income that would have been recognized	2,800,000	1,700,000	$ 2,300,000
Decrease in allowance for credit losses upon adoption of ASC 326	3,195,000
Provision for credit losses on loans	62,648,000	8,287,000
Interest income recognized on collateral-dependent loans	0
Interest income recognized on impaired loans		0
Commercial Real Estate
Financing Receivable Recorded Investment [Line Items]
Loans modification	81,700,000
U.S. Federal Agencies [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual loans guaranteed by government agencies	7,800,000
BancFirst [Member]
Financing Receivable Recorded Investment [Line Items]
Sale of Loans	21,600,000
Amount transferred from loans held for investment (net of unearned interest) to loans held for sale	$ 21,600,000
BancFirst’s [Member]
Financing Receivable Recorded Investment [Line Items]
Percentage of loans secured by real estate	58.00%
BancFirst’s [Member] \| Energy [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 191,000,000	189,000,000
BancFirst’s [Member] \| Energy [Member] \| Midstream Energy Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	50,000,000	41,000,000
BancFirst’s [Member] \| Commercial and Agricultural Non-Real Estate [Member] \| Ancillary Services [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	59,000,000	90,000,000
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	554,548,000	430,705,000
Decrease in allowance for credit losses upon adoption of ASC 326	(2,488,000)
Provision for credit losses on loans	1,886,000	569,000
Pegasus Bank [Member] \| Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 272,000,000
Percentage of loans secured by real estate	49.00%
Pegasus Bank [Member] \| Energy [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 107,000,000	57,000,000
Pegasus Bank [Member] \| Energy [Member] \| Midstream Energy Loans
Financing Receivable Recorded Investment [Line Items]
Total loans	11,000,000	0
Pegasus Bank [Member] \| Energy [Member] \| Ancillary Services [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	13,000,000	7,000,000
Pegasus Bank [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 262,000,000	$ 172,000,000