Note 9 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) by Component, Net of Tax (Details) - USD ($) $ 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
Balance	$ 88,544	$ 87,545	$ 85,858	$ 84,357	$ 82,089	$ 80,008	$ 85,858	$ 80,008
Net current period other comprehensive income (loss)	54	497	1,197	97	911	873
Balance	89,695	88,544	87,545	85,931	84,357	82,089	89,695	85,931
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Balance	1,586		(108)	267		(1,517)	(108)	(1,517)
Other comprehensive income before reclassification	54			130			2,250	1,915
Amounts reclassified from accumulated other comprehensive income (loss)				(33)			(502)	(34)
Net current period other comprehensive income (loss)	54			97			1,748	1,881
Balance	1,640	1,586		364	267		1,640	364
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(5,227)		(5,227)	(4,840)		(4,840)	(5,227)	(4,840)
Other comprehensive income before reclassification
Amounts reclassified from accumulated other comprehensive income (loss)
Net current period other comprehensive income (loss)
Balance	(5,227)	(5,227)		(4,840)	(4,840)		(5,227)	(4,840)
AOCI Attributable to Parent [Member]
Balance	(3,641)	(4,138)	(5,335)	(4,573)	(5,484)	(6,357)	(5,335)	(6,357)
Other comprehensive income before reclassification	54			130			2,250	1,915
Amounts reclassified from accumulated other comprehensive income (loss)				(33)			(502)	(34)
Net current period other comprehensive income (loss)	54	497	1,197	97	911	873	1,748	1,881
Balance	$ (3,587)	$ (3,641)	$ (4,138)	$ (4,476)	$ (4,573)	$ (5,484)	$ (3,587)	$ (4,476)