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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
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Contribution Plan Disclosure [Line Items]
Total contributions	$ 3,798banf_AggregateContributionByEmployer	$ 3,558banf_AggregateContributionByEmployer	$ 3,393banf_AggregateContributionByEmployer
401(k) contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Aggregate amounts of contributions	1,870us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember	1,738us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember	1,690us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_DefinedContributionPensionPlanFourZeroOneKMember
ESOP contributions [Member]
Defined Contribution Plan Disclosure [Line Items]
Aggregate amounts of contributions	$ 1,928us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember	$ 1,820us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember	$ 1,703us-gaap_DefinedContributionPlanEmployerDiscretionaryContributionAmount / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = banf_EmployeeStockOwnershipPlanMember

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- Definition

Aggregate contribution by employer.

+ References

No definition available.

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- Definition

Amount of discretionary contributions made by an employer to a defined contribution plan.

+ References

No definition available.

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