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Derivative Financial Instruments - Additional Information (Detail) | 12 Months Ended
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Dec. 31, 2017
Derivative Instruments And Hedging Activities Disclosure [Abstract] |
Company's share of total profit | 35.00%

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- Definition Profit share percentage. + References No definition available. + Details
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Namespace Prefix: | banf_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

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- References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration