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RETIREMENT FUND AND PROFIT SHARING PLAN (Details) - USD ($) $ in Thousands | 3 Months Ended | 9 Months Ended |
--- | --- | --- | ---
Sep. 30, 2016 | Sep. 30, 2015 | Sep. 30, 2016 | Sep. 30, 2015 | Dec. 31, 2015
Bel Fuse Inc Employees Savings Plan [Member] |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |
Compensation expense | $ 300 | $ 300 | $ 800 | $ 900 |
Bel Fuse Inc Employees Savings Plan [Member] | Class A Common Stock [Member] |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |
Shares owned by plan (in shares) | 13,928 |  | 13,928 |  |
Bel Fuse Inc Employees Savings Plan [Member] | Class B Common Stock [Member] |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |
Shares owned by plan (in shares) | 164,462 |  | 164,462 |  |
Non Defined Retirement Fund [Member] |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |
Compensation expense | $ 100 | 100 | $ 200 | 200 |
Non Defined Retirement Fund [Member] | Class A Common Stock [Member] |  |  |  |  |
Defined Contribution Plan Disclosure [Line Items] |  |  |  |  |
Shares owned by plan (in shares) | 3,323 |  | 3,323 |  |
Non Defined Retirement Fund [Member] | Class B Common Stock [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 | $ 148 | 138 | $ 445 | 414 |
Interest cost | 165 | 142 | 494 | 425 |
Net amortization | 98 | 92 | 293 | 275 |
Net periodic benefit cost | 411 | $ 372 | 1,232 | $ 1,114 |
Amounts recognized in accumulated other comprehensive loss, pretax [Abstract] |  |  |  |  |
Prior service cost | 730 |  | 730 |  | $ 866
Net loss | 2,900 |  | 2,900 |  | 3,465
Total amounts recognized in accumulated other comprehensive loss | $ 3,630 |  | $ 3,630 |  | $ 4,331

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- Definition The pretax total of net gain (loss), prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost. + References Reference 1: 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=65897934&loc=d3e1928-114920 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (i-k) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 + Details
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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=66004124&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=65897934&loc=d3e1928-114920 + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Prior Service Cost -URI http://asc.fasb.org/extlink&oid=49177896 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=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=66004124&loc=SL7669646-108580 + Details
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- Definition The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Service Cost (Component of Net Periodic Pension Cost) -URI http://asc.fasb.org/extlink&oid=6525008 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (h)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=65897934&loc=d3e1928-114920 + Details
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