RETIREMENT FUND AND PROFIT SHARING PLAN (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Balance sheet amounts [Abstract]
Minimum pension obligation and unfunded pension liability	$ 14,997		$ 14,997		$ 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			100.00%
Percentage of participant contribution under condition one	1.00%		1.00%
Employer match of the next 5% compensation contributed by participants			50.00%
Percentage of employee deferrals under condition two	5.00%		5.00%
Compensation expense	$ 300	$ 300	$ 900	$ 600
Bel Fuse Inc Employees Savings Plan [Member] | Asia [Member]
Defined Contribution Plan Disclosure [Line Items]
Maximum annual contribution by eligible employee			5.00%
Minimum employer contribution to plan			5.00%
Employer contribution of eligible salary			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)	169,989		169,989
Non Defined Retirement Fund [Member]
Defined Contribution Plan Disclosure [Line Items]
Compensation expense	$ 100	100	$ 200	200
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	$ 414	414
Interest cost	142	135	425	405
Net amortization	92	46	275	138
Net periodic benefit cost	372	$ 319	1,114	$ 957
Balance sheet amounts [Abstract]
Minimum pension obligation and unfunded pension liability	14,997		14,997		14,205
Amounts recognized in accumulated other comprehensive loss, pretax [Abstract]
Prior service cost	911		911		1,048
Net loss	3,164		3,164		3,302
Total amounts recognized in accumulated other comprehensive loss	$ 4,075		$ 4,075		$ 4,350

[1] Revised