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
	Mar. 31, 2019	Mar. 31, 2018
Balance	$ 80,008	$ 59,091
Net current period other comprehensive income (loss)	873	(1,015)
Cumulative effect of change in accounting principle for marketable equity securities, net of tax	(181)
Balance, as adjusted	79,827	59,091
Balance	82,089	58,877
AOCI, Accumulated Gain (Loss), Debt Securities, Available-for-sale, Parent [Member]
Balance	(1,517)	(679)
Other comprehensive income before reclassification	875	(1,021)
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	6
Net current period other comprehensive income (loss)	873	(1,015)
Cumulative effect of change in accounting principle for marketable equity securities, net of tax		(187)
Balance, as adjusted		(866)
Balance	(644)	(1,881)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(4,840)	(4,839)
Other comprehensive income before reclassification
Amounts reclassified from accumulated other comprehensive income (loss)
Net current period other comprehensive income (loss)
Cumulative effect of change in accounting principle for marketable equity securities, net of tax
Balance, as adjusted		(4,839)
Balance	(4,840)	(4,839)
AOCI Attributable to Parent [Member]
Balance	(6,357)	(5,518)
Other comprehensive income before reclassification	875	(1,021)
Amounts reclassified from accumulated other comprehensive income (loss)	(2)	6
Net current period other comprehensive income (loss)	873	(1,015)
Cumulative effect of change in accounting principle for marketable equity securities, net of tax		(187)
Balance, as adjusted	(6,357)	(5,705)
Balance	$ (5,484)	$ (6,720)