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Subsequent Event - Additional Information (Detail) - Subsequent Event [Member] $ in Millions | Jan. 12, 2018 USD ($)
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First Bank & Trust Company [Member] |
Subsequent Event [Line Items] |
Date of acquisition | Jan. 12, 2018
Total assets acquired | $ 287
Loans | 248
Deposits | 250
Equity capital | $ 36
First Bank of Chandler [Member] |
Subsequent Event [Line Items] |
Date of acquisition | Jan. 12, 2018
Total assets acquired | $ 86
Loans | 72
Deposits | 75
Equity capital | $ 11

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- Definition Business combination agreement to acquire assets. + References No definition available. + Details
Name: | banf_BusinessCombinationAgreementToAcquireAssets
Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Business combination agreement to acquire deposits. + References No definition available. + Details
Name: | banf_BusinessCombinationAgreementToAcquireDeposits
Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Business combination agreement to acquire equity capital. + References No definition available. + Details
Name: | banf_BusinessCombinationAgreementToAcquireEquityCapital
Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Business combination agreement to acquire loans. + References No definition available. + Details
Name: | banf_BusinessCombinationAgreementToAcquireLoans
Namespace Prefix: | banf_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Date when the acquirer obtains control of the acquiree, in CCYY-MM-DD format. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e845-128460 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 25 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=84229725&loc=d3e848-128460 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=banf_FirstBankAndTrustCompanyMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=banf_FirstBankOfChandlerMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |