Note 12 - Income Taxes (Details Textual) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024
Unrecognized Tax Benefits	$ 18.3		$ 18.1
Unrecognized Tax Benefits, Reduction From Lapse of Applicable Statue of Limitations	1.3
Unrecognized Tax Benefits, Income Tax Penalties and Interest Expense	0.1	$ 0.1
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 1.3		$ 1.2

Represents the amount of unrecognized tax benefits reduced due to a lapse of statue of limitations.

No definition available.

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Namespace Prefix:	belfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Amount of unrecognized tax benefits.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 55
-Paragraph 217
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482663/740-10-55-217

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 15A
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482685/740-10-50-15A

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 740
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 10B
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482525/740-10-45-10B

+ Details

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- Definition

Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

+ Details

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- Definition

Amount of expense for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return.

+ References

+ Details

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