Represents loans deferrals for accrued interest receivable of financing receivable.

No definition available.

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Namespace Prefix:	bfst_
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Period Type:	instant

- Definition

Loans and leases receivable reclassified from overdraft.

+ References

No definition available.

+ Details

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- Definition

Amount, after allowance for credit loss, of accrued interest on financing receivable.

+ References

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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
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+ Details

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Balance Type:	na
Period Type:	duration

- Definition

Amortized cost excluding accrued interest, of financing receivable 90 days or more past due and still accruing. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
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-Section 50
-Paragraph 16
-Subparagraph (c)
-Publisher FASB
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost excluding accrued interest, of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

+ Details

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

- Definition

Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
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-Name Regulation S-K (SK)
-Number 229
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+ Details

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Period Type:	instant

- Definition

Amount of unamortized loan commitment, origination, and other costs (fees) on financing receivable recognized as adjustment to yield. Excludes financing receivable covered under loss sharing agreement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 310
-SubTopic 20
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+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

This is the principal amount outstanding for securitized loans only (across all types of loans).

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 860
-SubTopic 20
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The cash inflow associated with the sale of loans receivables arising from the financing of goods and services.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 230
-SubTopic 10
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-URI https://asc.fasb.org/1943274/2147482740/230-10-45-12

+ Details

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Balance Type:	debit
Period Type:	duration

- Definition

Aggregate amount of servicing assets that are subsequently measured at fair value and servicing assets that are subsequently measured using the amortization method.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 820
-SubTopic 10
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-Subparagraph (b)
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-URI https://asc.fasb.org/1943274/2147481260/860-50-45-2

+ Details

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Balance Type:	debit
Period Type:	instant

- Details

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- Details

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Loans and the Allowance for Credit Losses - Narrative (Details) - USD ($)	1 Months Ended	9 Months Ended
	Jun. 30, 2026	Sep. 30, 2026	Sep. 30, 2025	Dec. 31, 2025
Financing Receivable, Allowance for Credit Loss [Line Items]
Financing receivable, unamortized loan cost (fee)		$ 9,900,000		$ 11,400,000
Loans and leases receivable reclassified from overdraft		1,300,000		7,900,000
Loan, securitized or asset-backed financing arrangement, principal outstanding		724,000,000.0		643,800,000
Servicing asset		1,600,000		956,000
Recorded investment outstanding more than 90 days past due and still accruing		3,701,000		2,215,000
Financing receivable, excluding accrued interest, nonaccrual		80,363,000		74,471,000
Financing receivable, nonaccrual		13,900,000		9,800,000
Financing receivable accrued interest receivable, loans deferrals		1,200,000		1,700,000
Financing receivable, accrued interest, after allowance for credit loss		34,700,000		$ 33,200,000
Proceeds from sale of loans		$ 83,304,000	$ 0
Progressive
Financing Receivable, Allowance for Credit Loss [Line Items]
Proceeds from sale of loans	$ 95,300,000
Residential \| Progressive
Financing Receivable, Allowance for Credit Loss [Line Items]
Proceeds from sale of loans	54,700,000
Commercial \| Progressive
Financing Receivable, Allowance for Credit Loss [Line Items]
Proceeds from sale of loans	$ 40,600,000