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Note 11 - Retirement Fund and Profit Sharing Plan (Details Textual) - USD ($) $ in Millions | 3 Months Ended | 9 Months Ended
--- | --- | ---
Sep. 30, 2021 | Sep. 30, 2020 | Sep. 30, 2021 | Sep. 30, 2020
Bel Fuse Inc. Employees' Savings Plan [Member] |  |  |  |
Defined Contribution Plan, Cost | $ 0.3 | $ 0.3 | $ 0.9 | $ 0.8
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class A [Member] |  |  |  |
Shares Held in Plan (in shares) | 292,569 |  | 292,569 |
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class B [Member] |  |  |  |
Shares Held in Plan (in shares) | 103,511 |  | 103,511 |
Retirement Fund Covering Hong Kong-based Employees [Member] |  |  |  |
Defined Contribution Plan, Cost | $ 0.6 | $ 0.1 | $ 1.9 | $ 0.2
Retirement Fund Covering Hong Kong-based Employees [Member] | Common Class A [Member] |  |  |  |
Shares Held in Plan (in shares) | 3,323 |  | 3,323 |
Retirement Fund Covering Hong Kong-based Employees [Member] | Common Class B [Member] |  |  |  |
Shares Held in Plan (in shares) | 17,342 |  | 17,342 |

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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 Amount of cost for defined contribution plan. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 70 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=49170846&loc=d3e28014-114942 + Details
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- Details
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