Document and Entity Information	3 Months Ended
	Mar. 31, 2015	May 01, 2015
Entity Information [Line Items]
Entity Registrant Name	BEL FUSE INC /NJ
Entity Central Index Key	0000729580
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Accelerated Filer
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2015
Class A Common Stock [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		2,174,912
Class B Common Stock [Member]
Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		9,656,777