Basis of presentation and summary of significant accounting policies.

No definition available.

Name:	banf_BasisOfPresentationAndSummaryOfSignificantAccountingPoliciesLineItems
Namespace Prefix:	banf_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Delinquency period placed on nonaccrual status loan.

+ References

No definition available.

+ Details

Name:	banf_DelinquencyPeriodPlacedOnNonaccrualStatusLoan
Namespace Prefix:	banf_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of available for sale securities held.

+ References

No definition available.

+ Details

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

- Definition

Percentage of processing fees.

+ References

No definition available.

+ Details

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

- Definition

Proceeds from processing fees.

+ References

No definition available.

+ Details

Name:	banf_ProceedsFromProcessingFees
Namespace Prefix:	banf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of the cumulative effect on retained earnings net of related income tax effect.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 250
-SubTopic 10
-Section 50
-Paragraph 9
-URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22663-107794

+ Details

Name:	us-gaap_CumulativeEffectOnRetainedEarningsNetOfTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Amount of the related income tax effect of a cumulative effect on retained earnings.

+ References

+ Details

Name:	us-gaap_CumulativeEffectOnRetainedEarningsTax1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of increase in allowance for credit loss on financing receivable purchased with credit deterioration.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 13
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919249-210447

+ Details

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

- Definition

Threshold period for when financing receivable is considered past due to write off as uncollectible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 20
-Section 50
-Paragraph 14
-URI http://asc.fasb.org/extlink&oid=119407570&loc=SL82919253-210447

+ Details

Name:	us-gaap_FinancingReceivableThresholdPeriodPastDueWriteoff
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of interest earned but not received. Also called accrued interest or accrued interest receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.8)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=banf_PaycheckProtectionProgramCARESActMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LoansInsuredOrGuaranteedByGovernmentAuthoritiesAxis=banf_SmallBusinessAdministrationSBAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AdjustmentsForNewAccountingPronouncementsAxis=us-gaap_AccountingStandardsUpdate201613Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=banf_USTreasurySecuritiesOrUSGovernmentSponsoredEntitiesAndAgenciesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Description of Business and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)		3 Months Ended	6 Months Ended	12 Months Ended
	Jan. 01, 2020	Jun. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Increase to retained earnings for cumulative effect of adopting ASU tax		$ 925,000
Addition to allowance for credit losses for financial assets purchased with credit deterioration			$ 502,000
Accrued interest receivable		31,000,000.0	$ 31,000,000.0	$ 27,400,000
Paycheck Protection Program, CARES Act [Member] \| Small Business Administration (SBA) [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of processing fees			5.00%
Processing fees received from the SBA			$ 30,000,000.0
ASU No. 2016-13 [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Increase to retained earnings for cumulative effect of adopting ASU	$ 2,300,000
Increase to retained earnings for cumulative effect of adopting ASU tax	925,000
Addition to allowance for credit losses for financial assets purchased with credit deterioration	$ 1,200,000
Accrued interest receivable		$ 31,000,000.0	$ 31,000,000.0
Delinquency period placed on nonaccrual status loan			90 days
Commercial loans are charged off deemed uncollectible period		180 days	180 days
ASU No. 2016-13 [Member] \| U.S. Treasury or U.S. Government-sponsored Entities and Agencies [Member]
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Percentage of available for sale securities held			95.00%	95.00%