Note 5 - Foreclosed Assets - Activity in the Valuation Allowance (Details) - USD ($)	12 Months Ended
Dec. 31, 2022	Dec. 31, 2021
Beginning balance	$ 227,000	$ 0
Additions charged to expense	31,000	420,000
Reductions from sales	(258,000)	(193,000)
Ending balance	$ 0	$ 227,000

Amount of the valuation allowance for foreclosed assets that was applied in the period against the carrying amount of foreclosed assets that was sold, written down or written off.

No definition available.

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