Name:	bfst_DepositsPublicFundsNonBrokered
Namespace Prefix:	bfst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Interest bearing deposits public funds brokered.

No definition available.

Name:	bfst_InterestBearingDepositsPublicFundsBrokered
Namespace Prefix:	bfst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

The percentage of certificate of deposit maturities at the next fiscal year following the latest fiscal year.

No definition available.

Name:	bfst_PercentageOfCertificateOfDepositMaturitiesYearOne
Namespace Prefix:	bfst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

The percentage of certificate of deposit maturities at year two and thereafter.

No definition available.

Name:	bfst_PercentageOfCertificateOfDepositMaturitiesYearTwoAndThereafter
Namespace Prefix:	bfst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

The percentage of interest and non-interest bearing domestic deposits to deposits.

No definition available.

Name:	bfst_PercentageOfInterestAndNonInterestBearingDomesticDepositsToDeposits
Namespace Prefix:	bfst_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

The aggregate of all deposit liabilities held by the entity, including foreign and domestic, interest and noninterest bearing; may include demand deposits, saving deposits, Negotiable Order of Withdrawal (NOW) and time deposits among others.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.12)
-Publisher FASB
-URI https://asc.fasb.org//1943274/2147479853/942-210-S99-1

Name:	us-gaap_Deposits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of interest-bearing domestic third-party deposits placed by or through the assistance of a deposit broker, also known as brokered deposit liabilities.