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, 2023	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2023	Sep. 30, 2022
Net earnings	$ 19,448	$ 27,775	$ 14,572	$ 16,548	$ 17,038	$ 5,064	$ 61,795	$ 38,649
Undistributed earnings	18,575			15,696			59,175	36,087
Common Class A [Member]
Net earnings	3,117			2,715			9,907	6,327
Less dividends declared	128	128	128	128	129	129	385	386
Undistributed earnings	$ 2,989			$ 2,587			$ 9,522	$ 5,941
Class A - basic and diluted (in shares)	2,142			2,142			2,142	2,144
Net earnings per common share - basic and diluted (in dollars per share)	$ 1.46			$ 1.27			$ 4.63	$ 2.95
Common Class B [Member]
Net earnings	$ 16,331			$ 13,833			$ 51,888	$ 32,322
Less dividends declared	745	$ 742	$ 747	724	$ 726	$ 727	2,235	2,176
Undistributed earnings	$ 15,586			$ 13,109			$ 49,653	$ 30,146
Class A - basic and diluted (in shares)	10,636			10,340			10,636	10,358
Net earnings per common share - basic and diluted (in dollars per share)	$ 1.54			$ 1.34			$ 4.88	$ 3.12