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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 |

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- Definition Amount transferred from loans held for investment net of unearned interest to loans held for sale. + References No definition available. + Details
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- Definition Collateral dependent loans financing receivable with related allowance interest income accrual method. + References No definition available. + Details
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- Definition Nonaccrual loan amount guaranteed by government agencies. + References No definition available. + Details
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- Definition Pay check protection program loan held for investment. + References No definition available. + Details
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- Definition Amount of credit loss expense (reversal of expense) for financing receivable from change in methodology. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 20 -Section 50 -Paragraph 11 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121599337&loc=SL82919244-210447 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 220 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.14(d)) -URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260 + Details
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- Definition 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). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=121585226&loc=d3e18794-111554 + Details
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- Definition 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. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=121593590&loc=d3e4428-111522 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=121611835&loc=d3e5074-111524 + Details
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