LEASES (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Jan. 01, 2019	Mar. 31, 2018
Leases [Abstract]
Gross carrying amount	$ 6,694	$ 6,700	$ 0
Accumulated amortization	(212)
Net book value	6,482
Right of use lease obligations	$ 6,482	$ 6,700

Operating Lease, Right-of-Use Asset, Accumulated Amortization

No definition available.

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- Definition

Operating Lease, Right-of-Use Asset, Net

+ References

No definition available.

+ Details

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Namespace Prefix:	bfin_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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- References

No definition available.

+ Details

Name:	us-gaap_LeasesAbstract
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- Definition

Present value of lessee's discounted obligation for lease payments from operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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

- Definition

Amount of lessee's right to use underlying asset under operating lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 842
-SubTopic 20
-Section 45
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=77888419&loc=SL77918627-209977

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	debit
Period Type:	instant