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

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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 loan held for sale.

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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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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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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 ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	$ 6,612,093		$ 6,612,093		$ 5,662,143
Pay check protection program loan held for investment	830,300		830,300
Paycheck protection program unamortized processing fees	22,500		22,500
Paycheck protection program loan held for sale	1,400		1,400
Paycheck protection program unamortized processing fees recognized as interest income			7,600
Interest income that would have been recognized			2,100	$ 1,400
Decrease in allowance for credit losses upon adoption of ASC 326			3,195
Provision for credit losses on loans	18,740	$ 2,758	57,656	6,875
Commercial Real Estate
Financing Receivable Recorded Investment [Line Items]
Loans modification	104,500		104,500
U.S. Federal Agencies [Member]
Financing Receivable Recorded Investment [Line Items]
Nonaccrual loans guaranteed by government agencies			8,400
BancFirst [Member]
Financing Receivable Recorded Investment [Line Items]
Sale of Loans	21,500		21,500
Amount transferred from loans held for investment (net of unearned interest) to loans held for sale	$ 21,500		$ 21,500
BancFirst’s [Member]
Financing Receivable Recorded Investment [Line Items]
Percentage of loans secured by real estate	50.00%		50.00%
BancFirst’s [Member] \| Commercial and Agricultural Non-Real Estate [Member] \| Ancillary Services [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	$ 80,000		$ 80,000		90,000
BancFirst’s [Member] \| Energy [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	219,000		219,000		189,000
BancFirst’s [Member] \| Energy [Member] \| Midstream Energy Loans
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	47,000		47,000		41,000
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	524,597		524,597		430,705
Decrease in allowance for credit losses upon adoption of ASC 326			(2,488)
Provision for credit losses on loans	528	$ 40	1,115	$ 40
Pegasus Bank [Member] \| Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	$ 266,000		$ 266,000
Percentage of loans secured by real estate	50.00%		50.00%
Pegasus Bank [Member] \| Commercial and Agricultural Non-Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	$ 242,000		$ 242,000		172,000
Pegasus Bank [Member] \| Energy [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	102,000		102,000		57,000
Pegasus Bank [Member] \| Energy [Member] \| Ancillary Services [Member]
Financing Receivable Recorded Investment [Line Items]
Loans (net of unearned interest)	$ 9,000		$ 9,000		$ 7,000