Percentage of loans secured by real estate.

No definition available.

Name:	banf_PercentageOfLoansSecuredByRealEstate
Namespace Prefix:	banf_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

Amount of interest income, recognized on accrual basis, on financing receivables, for which there is a related allowance for credit losses and are recognized as impaired.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeAccrualMethod
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118939409&loc=d3e18794-111554

+ Details

Name:	us-gaap_LoansAndLeasesReceivableImpairedInterestLostOnNonaccrualLoans
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount before allowance and after deduction of deferred interest and fees, unamortized costs and premiums and discounts from face amounts, of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Excludes loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=118952595&loc=d3e4428-111522

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5074-111524

+ Details

Name:	us-gaap_LoansAndLeasesReceivableNetOfDeferredIncome
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_BusinessAcquisitionAxis=banf_PegasusBankMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=banf_RealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CollateralAxis=banf_CommercialAndIndustrialMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=banf_AncillaryServicesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ProductOrServiceAxis=us-gaap_OilAndGasMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans and Allowance for Loan Losses - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 5,662,143,000	$ 4,975,976,000
Percentage of loans secured by real estate	58.00%
Interest income that would have been recognized	$ 1,700,000	2,300,000	$ 1,800,000
Interest income recognized on impaired loans	0	0
Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	430,705,000
Pegasus Bank [Member] \| Real Estate [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 237,000,000
Percentage of loans secured by real estate	55.00%
Commercial and Industrial [Member] \| Ancillary Services [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 93,000,000	$ 60,000,000
Commercial and Industrial [Member] \| Pegasus Bank [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	172,000,000
Commercial and Industrial [Member] \| Pegasus Bank [Member] \| Oil and Gas Industry [Member]
Financing Receivable Recorded Investment [Line Items]
Total loans	$ 44,000,000