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Loans and Allowance for Loan Losses - Internal Loan Grading by Class of Loans (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | $ 3,860,831 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount | $ 3,387,146 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount
Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 483,635 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember | 455,032 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember
Non-residential Real Estate Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 954,003 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember | 863,382 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember
Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 307,579 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember | 265,980 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember
Residential Real Estate All Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 637,088 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember | 567,873 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember
Non-consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 966,707 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember | 795,315 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember
Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 247,765 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember | 228,335 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember
Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 162,417 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember | 145,356 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember
Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 101,637 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember | 65,873 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember
Grade 1 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 3,258,055 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 2,898,156 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 402,706 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 382,798 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 795,209 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 711,081 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 272,411 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 233,924 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 529,555 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 475,421 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 821,094 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 691,772 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 233,424 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 214,153 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 157,191 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 141,787 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 1 [Member] | Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 46,465 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember | 47,220 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeOneMember
Grade 2 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 507,064 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 423,378 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 75,555 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 66,139 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 133,542 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 125,617 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 27,855 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 24,882 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 99,214 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 82,571 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 117,457 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 97,812 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 12,229 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 11,819 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 4,261 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 2,558 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 2 [Member] | Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 36,951 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember | 11,980 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeTwoMember
Grade 3 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 78,999 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 51,005 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 5,008 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 5,446 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 20,126 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 20,309 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 6,369 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 6,081 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 6,146 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 8,238 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 26,550 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 4,462 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 1,548 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 1,931 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 601 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 772 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 3 [Member] | Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 12,651 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember | 3,766 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeThreeMember
Grade 4 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 16,158 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 14,606 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Non-residential Real Estate Owner Occupied [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 366 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 649 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOwnerOccupiedMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Non-residential Real Estate Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 5,126 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 6,375 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonResidentialRealEstateOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Residential Real Estate Permanent Mortgage [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 944 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 1,093 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstatePermanentMortgageMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Residential Real Estate All Other [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 2,173 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 1,643 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ResidentialRealEstateAllOtherMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Non-consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 1,606 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 1,269 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_NonConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 564 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 431 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 173 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 239 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 4 [Member] | Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 5,206 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember | 2,907 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFourMember
Grade 5 [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 555 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeFiveMember | 1 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_InternalCreditAssessmentAxis = banf_GradeFiveMember
Grade 5 [Member] | Consumer Non-real Estate [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans |  | 1 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_ConsumerNonRealEstateMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFiveMember
Grade 5 [Member] | Other Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | 191 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_OtherLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFiveMember |
Grade 5 [Member] | Acquired Loans [Member] |  |
Financing Receivable, Allowance for Credit Losses [Line Items] |  |
Total loans | $ 364 us-gaap_LoansAndLeasesReceivableGrossCarryingAmount / us-gaap_FinancialInstrumentAxis = banf_AcquiredLoansMember / us-gaap_InternalCreditAssessmentAxis = banf_GradeFiveMember |

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- Definition Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522 + Details
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