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Retirement Plans - Aggregate Amounts of Contributions to the 401(k) and ESOP Plans (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Defined Contribution Plan Disclosure [Line Items] |  |  |
Total contributions | $ 3,798 banf_AggregateContributionByEmployer | $ 3,558 banf_AggregateContributionByEmployer | $ 3,393 banf_AggregateContributionByEmployer
401(k) contributions [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Aggregate amounts of contributions | 1,870 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember | 1,738 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember | 1,690 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember
ESOP contributions [Member] |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |
Aggregate amounts of contributions | $ 1,928 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember | $ 1,820 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember | $ 1,703 us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember

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- Definition Aggregate contribution by employer. + References No definition available. + Details
Name: | banf_AggregateContributionByEmployer
Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_DefinedContributionPlanDisclosureLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of discretionary contributions made by an employer to a defined contribution plan. + References No definition available. + Details
Name: | us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=banf_DefinedContributionPensionPlanFourZeroOneKMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis=banf_EmployeeStockOwnershipPlanMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |