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Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2014
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Days from origination after which mortgage loan are sold	30 days
Loan upon which a default of principal or interest has existed for a period	90 days
Intangible assets, Estimated useful lives	6 years 6 months
Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	5 years 10 months 24 days
Minimum [Member] | Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	7 years
Minimum [Member] | Customer Relationship Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	3 years
Maximum [Member] | Core Deposit Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	10 years
Maximum [Member] | Customer Relationship Intangibles [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Intangible assets, Estimated useful lives	18 years
First Liens [Member] | Minimum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	80.00%banf_LoansAndFinanceReceivablesPortfolioPercentage / us-gaap_DebtSecurityAxis = banf_FirstLienMember / us-gaap_RangeAxis = us-gaap_MinimumMember
Junior Liens [Member] | Maximum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	15.00%banf_LoansAndFinanceReceivablesPortfolioPercentage / us-gaap_DebtSecurityAxis = banf_JuniorLienMember / us-gaap_RangeAxis = us-gaap_MaximumMember
Home Equity Lines of Credit [Member] | Maximum [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Loans and finance receivables portfolio percentage	5.00%banf_LoansAndFinanceReceivablesPortfolioPercentage / us-gaap_DebtSecurityAxis = banf_HomeEquityLineOfCreditMember / us-gaap_RangeAxis = us-gaap_MaximumMember

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Period for sale of mortgage loan from origination.

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Period of default of principal or interest upon loan.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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