| Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] |
| | | Three Months Ended | | | Six Months Ended | |
| | | June 30, | | | June 30, | |
| | | 2026 | | | 2025 | | | 2026 | | | 2025 | |
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| Numerator: | | | | | | | | | | | | | | | | |
| Net earnings attributable to Bel Fuse shareholders | | $ | 25,480 | | | $ | 26,861 | | | $ | 36,859 | | | $ | 44,735 | |
| Less dividends declared: | | | | | | | | | | | | | | | | |
| Class A | | | 127 | | | | 127 | | | | 254 | | | | 254 | |
| Class B | | | 743 | | | | 740 | | | | 1,479 | | | | 1,477 | |
| Undistributed earnings attributable to Bel Fuse shareholders | | $ | 24,610 | | | $ | 25,994 | | | $ | 35,126 | | | $ | 43,004 | |
| | | | | | | | | | | | | | | | | |
| Undistributed earnings allocation: | | | | | | | | | | | | | | | | |
| Basic - Class A undistributed earnings | | $ | 3,673 | | | $ | 4,172 | | | $ | 5,429 | | | $ | 6,920 | |
| Basic - Class B undistributed earnings | | | 20,937 | | | | 21,822 | | | | 29,697 | | | | 36,084 | |
| Total undistributed earnings | | $ | 24,610 | | | $ | 25,994 | | | $ | 35,126 | | | $ | 43,004 | |
| | | | | | | | | | | | | | | | | |
| Net earnings allocation: | | | | | | | | | | | | | | | | |
| Basic - Class A net earnings | | $ | 3,800 | | | $ | 4,299 | | | $ | 5,683 | | | $ | 7,174 | |
| Basic - Class B net earnings | | | 21,680 | | | | 22,562 | | | | 31,176 | | | | 37,561 | |
| Basic - Net earnings | | $ | 25,480 | | | $ | 26,861 | | | $ | 36,859 | | | $ | 44,735 | |
| | | | | | | | | | | | | | | | | |
| Undistributed earnings allocation: | | | | | | | | | | | | | | | | |
| Diluted - Class A undistributed earnings | | $ | 3,669 | | | $ | 4,172 | | | $ | 5,425 | | | $ | 6,920 | |
| Diluted - Class B undistributed earnings | | | 20,941 | | | | 21,822 | | | | 29,701 | | | | 36,084 | |
| Total undistributed earnings | | $ | 24,610 | | | $ | 25,994 | | | $ | 35,126 | | | $ | 43,004 | |
| | | | | | | | | | | | | | | | | |
| Net earnings allocation: | | | | | | | | | | | | | | | | |
| Diluted - Class A net earnings | | $ | 3,796 | | | $ | 4,299 | | | $ | 5,679 | | | $ | 7,174 | |
| Diluted - Class B net earnings | | | 21,684 | | | | 22,562 | | | | 31,180 | | | | 37,561 | |
| Diluted - Net earnings | | $ | 25,480 | | | $ | 26,861 | | | $ | 36,859 | | | $ | 44,735 | |
| | | | | | | | | | | | | | | | | |
| Denominator: | | | | | | | | | | | | | | | | |
| Weighted-average shares outstanding: | | | | | | | | | | | | | | | | |
| Class A - Basic | | | 2,115 | | | | 2,115 | | | | 2,115 | | | | 2,115 | |
| Class A - Diluted | | | 2,115 | | | | 2,115 | | | | 2,115 | | | | 2,115 | |
| Class B - Basic | | | 11,483 | | | | 10,551 | | | | 11,020 | | | | 10,504 | |
| Class B - Diluted | | | 11,497 | | | | 10,551 | | | | 11,028 | | | | 10,504 | |
| | | | | | | | | | | | | | | | | |
| Net earnings per share: | | | | | | | | | | | | | | | | |
| Class A - Basic | | $ | 1.80 | | | $ | 2.03 | | | $ | 2.69 | | | $ | 3.39 | |
| Class A - Diluted | | $ | 1.79 | | | $ | 2.03 | | | $ | 2.68 | | | $ | 3.39 | |
| Class B - Basic | | $ | 1.89 | | | $ | 2.14 | | | $ | 2.83 | | | $ | 3.58 | |
| Class B - Diluted | | $ | 1.89 | | | $ | 2.14 | | | $ | 2.83 | | | $ | 3.58 | |
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