The value of customs duties and imposed fines.

No definition available.

Name:	belfa_CustomsDutiesAndImposedFines
Namespace Prefix:	belfa_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The period of indemnification.

+ References

No definition available.

+ Details

Name:	belfa_IndemnificationPeriod
Namespace Prefix:	belfa_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The amount of cash outflow for payment for customs duties and imposed fines and penalties.

+ References

No definition available.

+ Details

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

- Definition

The minimum amount the entity agreed to spend under the long-term purchase commitment.

+ References

No definition available.

+ Details

Name:	us-gaap_LongTermPurchaseCommitmentAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
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+ Details

Name:	us-gaap_LossContingencyEstimateOfPossibleLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Minimum amount to be expended to satisfy the terms of arrangements in which the entity has agreed to expend funds to procure goods or services, excluding long-term purchase commitments or unconditional purchase obligations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Topic 440
-SubTopic 10
-Name Accounting Standards Codification
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-Paragraph 4
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482648/440-10-50-4

+ Details

Name:	us-gaap_PurchaseCommitmentRemainingMinimumAmountCommitted
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	srt_LitigationCaseAxis=belfa_ArezzoRevenueAgencyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_LitigationCaseAxis=belfa_EOSClaimFromPrincipalCommissionerOfCustomsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=belfa_EOSPowerPanamaIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongTermPurchaseCommitmentByCategoryOfItemPurchasedAxis=us-gaap_CapitalAdditionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Note 19 - Commitments and Contingencies (Details Textual) - USD ($) $ in Millions	12 Months Ended			252 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2022	Dec. 31, 1994
Purchase Commitment, Remaining Minimum Amount Committed	$ 81.5	$ 82.2
Arezzo Revenue Agency [Member]
Loss Contingency, Estimate of Possible Loss					$ 12.0
EOS Claim From Principal Commissioner of Customs [Member] \| EOS Power Panama Inc. [Member]
Customs Duties and Imposed Fines			$ 0.9			$ 1.4
Payment for Customs Duties and Imposed Fines and Penalties				$ 0.5
Indemnification Period (Year)			7 years
Capital Addition Purchase Commitments [Member]
Long-Term Purchase Commitment, Amount	$ 2.0	$ 4.6