RETIREMENT FUND AND PROFIT SHARING PLAN (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Dec. 31, 2015
Bel Fuse Inc Employees Savings Plan [Member]
Defined Contribution Plan Disclosure [Line Items]
Compensation expense	$ 300	$ 300	$ 600	$ 600
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)	168,248		168,248
Non Defined Retirement Fund [Member]
Defined Contribution Plan Disclosure [Line Items]
Compensation expense	$ 100	100	$ 100	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	$ 148	138	$ 296	276
Interest cost	165	142	330	283
Net amortization	98	92	196	183
Net periodic benefit cost	411	$ 372	822	$ 742
Amounts recognized in accumulated other comprehensive loss, pretax [Abstract]
Prior service cost	775		775		$ 866
Net loss	2,952		2,952		3,465
Total amounts recognized in accumulated other comprehensive loss	$ 3,727		$ 3,727		$ 4,331