Note 15 - Retirement Fund and Profit Sharing Plan (Details Textual) $ in Thousands	12 Months Ended		24 Months Ended
	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2023 USD ($) shares
Supplemental Employee Retirement Plan [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense			$ 100
Defined Benefit Plan, Percentage of Average Base Compensation Five Consecutive Years, Normal Retirement	40.00%
Defined Benefit Plan, Number of Monthly Payments	120
Percentage of Participant's Annual Base Salary Received by Beneficiary, One Year From Date of Death	100.00%
Percentage of Participant's Annual Base Salary Received by Beneficiary, Following Four Years From Date of Death	50.00%
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	$ 1,326	$ 1,451
Defined Benefit Plan, Accumulated Benefit Obligation	18,100	17,000	18,100
Investments, Fair Value Disclosure	15,400	14,000	15,400
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year	800		800
Defined Benefit Plan, Plan Assets, Amount, Ending Balance	$ 0		$ 0
Bel Fuse Inc. Employees' Savings Plan [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent Of Match, First 1% Employee Contribution	100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match, Next 5% Employee Contribution	50.00%
Defined Contribution Plan, Cost	$ 1,300	1,300
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class A [Member]
Shares Held in Plan (in shares) | shares	287,777		287,777
Bel Fuse Inc. Employees' Savings Plan [Member] | Common Class B [Member]
Shares Held in Plan (in shares) | shares	65,089		65,089
Nonqualified Deferred Compensation Plan [Member]
Deferred Compensation Arrangement, Vesting Age	65		65
Deferred Compensation Plan Assets	$ 1,000	700	$ 1,000
Nonqualified Deferred Compensation Plan [Member] | Maximum [Member]
Deferred Compensation Arrangement with Individual, Compensation Expense	200	100
Retirement Fund Covering Hong Kong-based Employees [Member]
Defined Contribution Plan, Cost	$ 1,500	$ 1,800
Defined Contribution Plan, Maximum Annual Contributions Per Employee, Percent	5.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	7.00%
Retirement Fund Covering Hong Kong-based Employees [Member] | Minimum [Member]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	5.00%
Retirement Fund Covering Hong Kong-based Employees [Member] | Common Class A [Member]
Shares Held in Plan (in shares) | shares	0	3,323	0
Retirement Fund Covering Hong Kong-based Employees [Member] | Common Class B [Member]
Shares Held in Plan (in shares) | shares		17,342