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Loans and Allowance for Loan Losses - Additional Information (Detail) (USD $) | 3 Months Ended
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Mar. 31, 2015 SecurityLoan | Mar. 31, 2014
Receivables [Abstract] |  |
Percentage of loans secured by real estate | 65.00%banf_PercentageOfLoansSecuredByRealEstate |
Interest income recognized | $ 310,000 us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans | $ 227,000 us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Troubled debt restructuring principal deferral | 1 us-gaap_FinancingReceivableModificationsNumberOfContracts2 |

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- Definition Percentage of loans secured by real estate. + References No definition available. + Details
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Namespace Prefix: | banf_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Number of financing receivables that have been modified by troubled debt restructurings. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 50 -Paragraph 33 -URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953676-111524 + Details
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Namespace Prefix: | us-gaap_
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Period Type: | duration

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- Definition Reflects the amount of additional interest income that would have been recorded if impaired or nonperforming loans were instead current, in compliance with their original terms, and outstanding throughout the reporting period or since origination (if held for part of the period). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 40 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554 + Details
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Namespace Prefix: | us-gaap_
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Balance Type: | credit
Period Type: | duration

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- Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
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Period Type: | duration