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Commitments and Contingent Liabilities - Summary of Financial Instruments with Off-Balance-Sheet Risks (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Loan commitments	$ 1,618,001	$ 1,232,996
Stand-by letters of credit	$ 64,702	$ 56,096

X

- Definition

Unfunded loan commitments.

+ References

No definition available.

+ Details

Name:	banf_UnfundedLoanCommitments
Namespace Prefix:	banf_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- References

No definition available.

+ Details

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

X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

Name:	us-gaap_LettersOfCreditOutstandingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant