Note 1 - Description of Business and Summary of Significant Accounting Policies - Basic and Diluted Net Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Net earnings attributable to Bel shareholders	$ 40,960	$ 73,831	$ 52,689
Undistributed earnings	37,521	70,322	49,253
Common Class A [Member]
Net earnings attributable to Bel shareholders	6,572	11,830	8,598
Less dividends declared	508	512	514
Undistributed earnings	$ 6,064	$ 11,318	$ 8,084
Weighted-average number of shares outstanding - basic and diluted (in shares)	2,124	2,142	2,143
Net earnings per share, basic and diluted (in dollars per share)	$ 3.1	$ 5.52	$ 4.01
Common Class B [Member]
Net earnings attributable to Bel shareholders	$ 34,388	$ 62,001	$ 44,091
Less dividends declared	2,931	2,997	2,922
Undistributed earnings	$ 31,457	$ 59,004	$ 41,169
Weighted-average number of shares outstanding - basic and diluted (in shares)	10,491	10,634	10,394
Net earnings per share, basic and diluted (in dollars per share)	$ 3.28	$ 5.83	$ 4.24