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RETIREMENT FUND AND PROFIT SHARING PLAN (Details) - USD ($) $ in Thousands | 3 Months Ended | 6 Months Ended |
--- | --- | --- | ---
Jun. 30, 2015 | Jun. 30, 2014 | Jun. 30, 2015 | Jun. 30, 2014 | Dec. 31, 2014
Balance sheet amounts [Abstract] |  |  |  |  |  |
Minimum pension obligation and unfunded pension liability | $ 14,733 |  | $ 14,733 |  | $ 14,205 | [1]
Bel Fuse Inc Employees Savings Plan [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Employer match of the first 1% of compensation contributed by participants (in hundredths) |  |  | 100.00% |  |  |
Percentage of participant contribution under condition one (in hundredths) | 1.00% |  | 1.00% |  |  |
Employer match of the next 5% compensation contributed by participants (in hundredths) |  |  | 50.00% |  |  |
Percentage of employee deferrals under condition two (in hundredths) | 5.00% |  | 5.00% |  |  |
Compensation expense | $ 300 | $ 100 | $ 600 | $ 300 |  |
Maximum annual contribution by eligible employee (in hundredths) |  |  | 5.00% |  |  |
Minimum employer contribution to plan (in hundredths) |  |  | 5.00% |  |  |
Employer contribution of eligible salary (in hundredths) |  |  | 7.00% |  |  |
Bel Fuse Inc Employees Savings Plan [Member] | Common Class A [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Shares owned by plan (in shares) | 13,928 |  | 13,928 |  |  |
Bel Fuse Inc Employees Savings Plan [Member] | Common Class B [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Shares owned by plan (in shares) | 172,269 |  | 172,269 |  |  |
Non Defined Retirement Fund [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Compensation expense | $ 100 | 100 | $ 200 | 100 |  |
Non Defined Retirement Fund [Member] | Common Class A [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Shares owned by plan (in shares) | 3,323 |  | 3,323 |  |  |
Non Defined Retirement Fund [Member] | Common Class B [Member] |  |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |  |
Shares owned by plan (in shares) | 17,342 |  | 17,342 |  |  |
SERP [Member] |  |  |  |  |  |
Components of SERP expense [Abstract] |  |  |  |  |  |
Service cost | $ 138 | 138 | $ 276 | 276 |  |
Interest cost | 142 | 135 | 283 | 270 |  |
Net amortization | 92 | 46 | 183 | 92 |  |
Net periodic benefit cost | 372 | $ 319 | 742 | $ 638 |  |
Balance sheet amounts [Abstract] |  |  |  |  |  |
Minimum pension obligation and unfunded pension liability | 14,733 |  | 14,733 |  | 14,205 |
Amounts recognized in accumulated other comprehensive loss, pretax [Abstract] |  |  |  |  |  |
Prior service cost | 957 |  | 957 |  | 1,048 |
Net loss | 3,210 |  | 3,210 |  | 3,302 |
Total amounts recognized in accumulated other comprehensive loss | $ 4,167 |  | $ 4,167 |  | $ 4,350 |
[1] | Revised

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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=36458714&loc=SL7669646-108580 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920 + Details
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