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Retirement Plans - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2020 Plans
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |
Number of retirement plans | 2
Maximum [Member] |
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] |
Maximum legal limit of employer contribution to plan | 3.00%

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- Definition Defined benefit plans and other postretirement benefit plans. + References No definition available. + Details
Name: | banf_DefinedBenefitPlansAndOtherPostretirementBenefitPlansLineItems
Namespace Prefix: | banf_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Number of retirement plans. + References No definition available. + Details
Name: | banf_NumberOfRetirementPlans
Namespace Prefix: | banf_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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- Definition Percentage employer matches of the employee's percentage contribution matched. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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