Note 5 - Earnings Per Share - Basic and Diluted Net Earnings Per Common Share (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2024	Jun. 30, 2024	Mar. 31, 2024	Sep. 30, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2024	Sep. 30, 2023
Net earnings	$ 8,080	$ 18,806	$ 15,874	$ 19,448	$ 27,775	$ 14,572	$ 42,760	$ 61,795
Undistributed earnings	7,240			18,575			40,189	59,175
Common Class A [Member]
Net earnings	1,297			3,117			6,872	9,907
Less dividends declared	125	127	129	128	128	128	381	385
Undistributed earnings	$ 1,172			$ 2,989			$ 6,491	$ 9,522
Class A - basic and diluted (in shares)	2,116			2,142			2,126	2,142
Net earnings per common share - basic and diluted (in dollars per share)	$ 0.61			$ 1.46			$ 3.23	$ 4.63
Common Class B [Member]
Net earnings	$ 6,783			$ 16,331			$ 35,888	$ 51,888
Less dividends declared	715	$ 725	$ 747	745	$ 742	$ 747	2,190	2,235
Undistributed earnings	$ 6,068			$ 15,586			$ 33,698	$ 49,653
Class A - basic and diluted (in shares)	10,434			10,636			10,512	10,636
Net earnings per common share - basic and diluted (in dollars per share)	$ 0.65			$ 1.54			$ 3.41	$ 4.88