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

X

- Definition

Profit share percentage.

+ References

No definition available.

+ Details

Name:	banf_ProfitSharePercentage
Namespace Prefix:	banf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

X

- References

No definition available.

+ Details

Name:	us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosureAbstract
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration