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Stockholders' Equity - Additional Information (Detail) | Mar. 31, 2021 USD ($)
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Small Business Administration (SBA), CARES Act, Paycheck Protection Program Lending Facility [Member] |
Stockholders Equity [Line Items] |
Percentage of risk weight under risk based capital rules | 0.00%
Maximum [Member] |
Stockholders Equity [Line Items] |
Quantitative limit for trust preferred securities to be included in tier 1 capital | $ 15,000,000,000

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- Definition Percentage of risk weight under risk-based capital rules. + References No definition available. + Details
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Namespace Prefix: | banf_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Quantitative limit for trust preferred securities to be included in tier one capital. + References No definition available. + Details
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Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Stockholders equity. + References No definition available. + Details
Name: | banf_StockholdersEquityLineItems
Namespace Prefix: | banf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=banf_SmallBusinessAdministrationCARESActPaycheckProtectionProgramLendingFacilityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |