Note 4 - Earnings (Loss) 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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Net earnings (loss)	$ 7,475	$ 5,573	$ (3,804)	$ (6,490)	$ 2,967	$ 1,131	$ 9,244	$ (2,391)
Undistributed earnings (loss)	6,629			(7,331)			6,723	(4,907)
Common Class A [Member]
Net earnings (loss)	1,233			(1,112)			1,512	(442)
Less dividends declared	129	129	130	131	131	130	388	392
Undistributed earnings (loss)	$ 1,104			$ (1,243)			$ 1,124	$ (834)
Weighted-average shares outstanding, basic and diluted (in shares)	2,145			2,173			2,145	2,174
Common shares - basic and diluted (in dollars per share)	$ 0.57			$ (0.51)			$ 0.70	$ (0.20)
Common Class B [Member]
Net earnings (loss)	$ 6,242			$ (5,378)			$ 7,732	$ (1,949)
Less dividends declared	717	$ 707	$ 709	710	$ 704	$ 708	2,133	2,124
Undistributed earnings (loss)	$ 5,525			$ (6,088)			$ 5,599	$ (4,073)
Weighted-average shares outstanding, basic and diluted (in shares)	10,223			10,139			10,176	10,113
Common shares - basic and diluted (in dollars per share)	$ 0.61			$ (0.53)			$ 0.76	$ (0.19)