Note 4 - 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, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Net earnings	$ 5,734	$ 7,880	$ 3,199	$ 7,475	$ 5,573	$ (3,804)	$ 16,813	$ 9,244
Undistributed earnings	4,886			6,629			14,278	6,723
Common Class A [Member]
Net earnings	940			1,233			2,761	1,512
Less dividends declared	129	129	128	129	129	130	386	388
Undistributed earnings	$ 811			$ 1,104			$ 2,375	$ 1,124
Weighted-average shares outstanding, basic and diluted (in shares)	2,145			2,145			2,145	2,145
Common shares - basic and diluted (in dollars per share)	$ 0.44			$ 0.57			$ 1.29	$ 0.70
Common Class B [Member]
Net earnings	$ 4,794			$ 6,242			$ 14,052	$ 7,732
Less dividends declared	719	$ 714	$ 716	717	$ 707	$ 709	2,149	2,133
Undistributed earnings	$ 4,075			$ 5,525			$ 11,903	$ 5,599
Weighted-average shares outstanding, basic and diluted (in shares)	10,269			10,223			10,237	10,176
Common shares - basic and diluted (in dollars per share)	$ 0.47			$ 0.61			$ 1.37	$ 0.76