Note 5 - Foreclosed Assets - Real Estate Acquired Through Foreclosure (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Foreclosed assets - Nonresidential real estate OREO	$ 274	$ 0
Foreclosed assets - Nonresidential real estate OREO	0	0
Foreclosed assets - Nonresidential real estate OREO	274	0
Other foreclosed assets, gross	913	952
Other foreclosed assets, valuation allowance	(219)	(227)
Other foreclosed assets	694	725
Other real estate owned and other foreclosed assets, gross	1,187	952
Other real estate owned and other foreclosed assets, valuation allowance	(219)	(227)
Total	$ 968	$ 725

Represents gross amount of other foreclosed assets.

No definition available.

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

- Definition

Represents valuation allowance of other foreclosed assets.

+ References

No definition available.

+ Details

Name:	bfin_OtherForeclosedAssetsValuationAllowanceEndingBalance
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Represents gross amount of other real estate owned and other foreclosed assets.

+ References

No definition available.

+ Details

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

- Definition

Carrying amount of other real estate not separately disclosed, including, but not limited to, real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned, before valuation allowance.

+ References

No definition available.

+ Details

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

- Definition

Represents valuation allowance for both real estate owned and other foreclosed assets.

+ References

No definition available.

+ Details

Name:	bfin_RealEstateOwnedAndOtherForeclosedAssetsValuationAllowanceEndingBalance
Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Carrying amount as of the balance sheet date of assets other than real property that were received in full or partial satisfaction of a debt arrangement through foreclosure proceedings or defeasance.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11
-URI https://asc.fasb.org/extlink&oid=123577603&loc=d3e5162-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 45
-Paragraph 3
-URI https://asc.fasb.org/extlink&oid=124259787&loc=d3e4437-111522

+ Details

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

- Definition

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.10(4))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

+ Details

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

- Definition

Carrying amount as of the balance sheet date of other real estate and foreclosed assets. Other real estate may include real estate investments, real estate loans that qualify as investments in real estate, and premises that are no longer used in operations may also be included in real estate owned. Foreclosed assets include all assets obtained in full or partial satisfaction of a debt arrangement through foreclosure proceedings.

+ References

+ Details

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

- Definition

For each period for which an income statement is required, disclosure of the changes in the allowance, including balances at end of period.

+ References

+ Details

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