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Derivative Financial Instruments - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2025	Dec. 31, 2024
Derivative [Line Items]
Percentage share of total profit	35.00%
Other Assets [Member] | Oil and Gas Reserves [Member]
Derivative [Line Items]
Derivative instrument asset margin amount	$ 48,000	$ 463,000

X

- Definition

Derivative iasset margin amount.

+ References

No definition available.

+ Details

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Namespace Prefix:	banf_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Derivative instrument, percentage of share profit.

+ References

No definition available.

+ Details

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Namespace Prefix:	banf_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

X

- 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

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 815
-SubTopic 20
-Name Accounting Standards Codification
-Section 25
-Paragraph 6A
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480682/815-20-25-6A

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
-SubTopic 40
-Name Accounting Standards Codification
-Section 50
-Paragraph 5
-Subparagraph (f)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480237/815-40-50-5

+ Details

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Period Type:	duration

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- Details

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Namespace Prefix:
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X

- Details

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Namespace Prefix:
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Balance Type:
Period Type: