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Data Type:	xbrli:monetaryItemType
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Amount of interest income recognized on a cash-basis method of accounting that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

No definition available.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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Amount of balance of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableLoanBalance
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of partial charge offs for impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivablePartialChargeOffs
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Data Type:	xbrli:monetaryItemType
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Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableRecordedInvestment1
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Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of allowance for credit losses related to recorded investment.

No definition available.

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Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of average investment of impaired financing receivables for which there is no related allowance for credit losses.

No definition available.

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Data Type:	xbrli:monetaryItemType
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Amount of interest income, recognized on cash basis, on financing receivables, for which there is no related allowance for credit losses and are recognized as impaired.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithNoRelatedAllowanceInterestIncomeCashBasisMethod1
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of partial charge offs for impaired financing receivables for which there is no related allowance for credit losses

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithNoRelatedAllowancePartialChargeOff
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
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Period Type:	instant

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment1
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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance1
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of average investment of impaired financing receivables for which there is a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithRelatedAllowanceAverageRecordedInvestment1
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Amount of interest income on financing receivables, for which there is a related allowance for credit losses, recognized on a cash-basis method of accounting that the financing receivables were impaired.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithRelatedAllowanceInterestIncomeCashBasisMethod1
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

Amount of balance in impaired financing receivables for which there is a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithRelatedAllowanceLoanBalance
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of partial charge offs for impaired financing receivables with related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithRelatedAllowancePartialChargeOff
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

No definition available.

Name:	bfin_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment1
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

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Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bfin_OneToFourFamilyResidentialRealEstateLoansMember
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Data Type:	na
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Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=bfin_RealEstatePortfolioMember
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Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=bfin_MultifamilyMortgageMember
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