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v3.19.1

Securities - Additional Information (Detail) $ in Millions | Mar. 31, 2019 USD ($)
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Accrued Interest Receivable and Other Assets [Member] |
Schedule of Available-for-sale Securities [Line Items] |
Securities matured | $ 50.0

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- Definition Non-cash investing activities securities matured. + References No definition available. + Details
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Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BalanceSheetLocationAxis=banf_AccruedInterestReceivableAndOtherAssetsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |