v2.4.0.6
Document and Entity Information (USD $)
6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Aug. 01, 2012
Class A Common Stock [Member]
Aug. 01, 2012
Class B Common Stock [Member]
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      
Entity Common Stock, Shares Outstanding     2,174,912 9,725,543
Document Fiscal Year Focus 2012      
Document Fiscal Period Focus Q2      
Document Type 10-Q      
Amendment Flag false      
Document Period End Date Jun. 30, 2012      
Entity Public Float   $ 239,000,000