v2.4.0.6
Document and Entity Information (USD $)
3 Months Ended
Mar. 31, 2012
Jun. 30, 2011
May 01, 2012
Common Class A [Member]
May 01, 2012
Common Class B [Member]
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 Public Float   $ 239,000,000    
Entity Common Stock, Shares Outstanding     2,174,912 9,627,693
Document Fiscal Year Focus 2012      
Document Fiscal Period Focus Q1      
Document Type 10-Q      
Amendment Flag false      
Document Period End Date Mar. 31, 2012