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Note 13 - Retirement, Savings and Deferred Compensation Plans (Details Textual) $ in Millions | 3 Months Ended |
--- | --- | ---
Mar. 31, 2025 USD ($) shares | Mar. 31, 2024 USD ($) | Dec. 31, 2024 USD ($)
Supplemental Employee Retirement Plan [Member] |  |  |
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 0.1 | $ 0.1 |
Bel Fuse Inc. Employees' Savings Plan [Member] |  |  |
Defined Contribution Plan, Cost | $ 0.4 | 0.6 |
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class A [Member] |  |  |
Shares Held in Plan (in shares) | shares | 255,197 |  |
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class B [Member] |  |  |
Shares Held in Plan (in shares) | shares | 51,942 |  |
Nonqualified Deferred Compensation Plan [Member] |  |  |
Deferred Compensation Arrangement, Vesting Age | 65 |  |
Deferred Compensation Plan Assets | $ 1.3 |  | $ 1.3
Nonqualified Deferred Compensation Plan [Member] | Maximum [Member] |  |  |
Deferred Compensation Arrangement with Individual, Compensation Expense | $ 0.1 | $ 0.1 |

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- Definition The age of employees for contributions to become fully vested under deferred compensation arrangement. + References No definition available. + Details
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- Definition The number of shares of the company's common stock owned by the plan. + References No definition available. + Details
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- Definition The compensation expense recognized during the period pertaining to the deferred compensation arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Topic 710 -SubTopic 10 -Name Accounting Standards Codification -Section 30 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147483043/710-10-30-1 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480429/718-10-50-1 + Details
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- Definition Carrying amount as of the balance sheet date of assets held under deferred compensation agreements. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(17)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 + Details
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- Definition Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Topic 715 -SubTopic 70 -Name Accounting Standards Codification -Section 50 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147480794/715-70-50-1 + Details
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