Note 17 - Revisions of Previously Issued Unaudited Consolidated Financial Statements (Unaudited) - Balance Sheets (Details) - USD ($)	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021		Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020
Equity investment in unconsolidated affiliate	$ 4,718,000	$ 4,783,000	$ 4,932,000	$ 5,147,000,000	$ 5,251,000		$ 5,183,000	$ 5,257,000	$ 4,990,000,000
Total assets	64,803,000	65,081,000	66,694,000	66,747,000,000	67,020,000		67,025,000	66,804,000	67,573,000,000
Retained earnings	62,124,000	62,559,000	63,108,000	63,311,000,000	62,488,000		62,596,000	62,130,000	61,648,000,000
Accumulated other comprehensive loss	(1,489,000)	(1,424,000)	(1,287,000)	(1,022,000,000)	(869,000)		(989,000)	(802,000)	(881,000,000)
Total shareholders' equity	60,758,000	61,261,000	61,949,000	62,419,000,000	61,751,000		61,739,000	61,460,000	60,901,000,000	$ 58,757,000
Total liabilities and shareholders' equity	$ 64,803,000	65,081,000	66,694,000	66,747,000,000	67,020,000		67,025,000	66,804,000	67,573,000,000
Previously Reported [Member]
Equity investment in unconsolidated affiliate		6,207,000	6,219,000	6,169,000,000	6,120,000		6,172,000	6,059,000	5,871,000,000
Total assets		66,505,000	67,981,000	67,769,000,000	67,889,000		68,014,000	67,606,000	68,454,000,000
Retained earnings		62,559,000	63,108,000	63,311,000,000	62,488,000		62,596,000	62,130,000	61,648,000,000
Accumulated other comprehensive loss		0	0	0	0		0	0	0
Total shareholders' equity		62,685,000	63,236,000	63,441,000,000	62,620,000		62,728,000	62,262,000	61,782,000,000
Total liabilities and shareholders' equity		66,505,000	67,981,000	67,769,000,000	67,889,000		68,014,000	67,606,000	68,454,000,000
Revision of Prior Period, Adjustment [Member]
Equity investment in unconsolidated affiliate		(1,424,000)	(1,287,000)	(1,022,000,000)	(869,000)	[1]	(989,000)	(802,000)	(881,000,000)
Total assets		(1,424,000)	(1,287,000)	(1,022,000,000)	(869,000)	[1]	(989,000)	(802,000)	(881,000,000)
Retained earnings		0	0	0	0	[1]	0	0	0
Accumulated other comprehensive loss		(1,424,000)	(1,287,000)	(1,022,000,000)	(869,000)	[1]	(989,000)	(802,000)	(881,000,000)
Total shareholders' equity		(1,424,000)	(1,287,000)	(1,022,000,000)	(869,000)	[1]	(989,000)	(802,000)	(881,000,000)
Total liabilities and shareholders' equity		$ (1,424,000)	$ (1,287,000)	$ (1,022,000,000)	$ (869,000)	[1]	$ (989,000)	$ (802,000)	$ (881,000,000)

[1] Equity investment in unconsolidated affiliate and accumulated other comprehensive loss have been adjusted by a total of $869,000, of which $773,000 pertains to periods prior to 2021 and $96,000 pertains to 2021.