Note 5 - Foreclosed Assets - Activity in the Valuation Allowance (Details) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2025	Sep. 30, 2024
Beginning balance	$ 0	$ 0	$ 0	$ 111
Reductions from sales	0	0	0	(111)
Ending balance	$ 0	$ 0	$ 0	$ 0

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