Note 9 - Accrued Expenses (Details Textual) $ in Millions	3 Months Ended
Mar. 31, 2025 USD ($)
Restrucruting Costs, Reversal	$ 3.2

The amount of restructuring costs reversed during the period.

No definition available.

Name:	belfa_RestrucrutingCostsReversal
Namespace Prefix:	belfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration