Note 14 - Accumulated Other Comprehensive Loss - Accumulated Other Comprehensive Loss (Details) (Parentheticals) - USD ($) $ in Thousands	Sep. 30, 2023	Dec. 31, 2022
Foreign currency translation adjustment, tax	$ (260)	$ (369)
Unrealized gains (losses) on interest rate swap cash flow hedge, tax	0	0
Unrealized holding gains on available-for-sale securities, tax	(7)	(7)
Change in unfunded SERP liabilityChange in unfunded SERP liability, tax, tax	$ 891	$ 879

Represents the tax portion in relation to net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other post-retirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

No definition available.

Name:	belfa_AccumulatedOtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansTax
Namespace Prefix:	belfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant