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				6 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2021	Jun. 30, 2020
Net earnings	$ 7,880	$ 3,199	$ 5,573	$ (3,804)	$ 11,080	$ 1,769
Undistributed earnings	7,037		4,737		9,393	94
Common Class A [Member]
Net earnings	1,299		923		1,822	274
Less dividends declared	129	128	129	130	257	259
Undistributed earnings	$ 1,170		$ 794		$ 1,565	$ 15
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)	$ 0.61		$ 0.43		$ 0.85	$ 0.13
Common Class B [Member]
Net earnings	$ 6,581		$ 4,650		$ 9,258	$ 1,495
Less dividends declared	714	$ 716	707	$ 709	1,430	1,416
Undistributed earnings	$ 5,867		$ 3,943		$ 7,828	$ 79
Weighted-average shares outstanding, basic and diluted (in shares)	10,237		10,178		10,220	10,151
Common shares - basic and diluted (in dollars per share)	$ 0.64		$ 0.46		$ 0.91	$ 0.15