v3.25.2
Document And Entity Information - shares
 6 Months Ended
Jun. 30, 2025
Jul. 25, 2025
Document Information [Line Items]    
Entity Central Index Key 0000729580  
Entity Registrant Name BEL FUSE INC /NJ  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Document Fiscal Period Focus Q2  
Document Fiscal Year Focus 2025  
Document Type 10-Q  
Document Quarterly Report true  
Document Period End Date Jun. 30, 2025  
Document Transition Report false  
Entity File Number 000-11676  
Entity Incorporation, State or Country Code NJ  
Entity Tax Identification Number 22-1463699  
Entity Address, Address Line One 300 Executive Drive, Suite 300  
Entity Address, City or Town West Orange  
Entity Address, State or Province NJ  
Entity Address, Postal Zip Code 07052  
City Area Code 201  
Local Phone Number 432-0463  
Entity Current Reporting Status Yes  
Entity Interactive Data Current Yes  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Common Class B [Member]    
Document Information [Line Items]    
Title of 12(b) Security Class B Common Stock ($0.10 par value)  
Trading Symbol BELFB  
Security Exchange Name NASDAQ  
Entity Common Stock, Shares Outstanding   10,548,254
Common Class A [Member]    
Document Information [Line Items]    
Title of 12(b) Security Class A Common Stock ($0.10 par value)  
Trading Symbol BELFA  
Security Exchange Name NASDAQ  
Entity Common Stock, Shares Outstanding   2,115,263