Note 12 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Balance			$ 513,853	$ 473,067
Net current period other comprehensive income, net of tax	$ (88)	$ (2,839)	1,698	5,811
Balance	539,609	512,621	539,609	512,621
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	(2,110)	7,923	(3,859)	(521)
Other comprehensive income before reclassifications, net of tax	(333)	(2,942)	1,416	6,852
Amounts reclassified from accumulated other comprehensive income, net of tax	108		108	(1,350)
Net current period other comprehensive income, net of tax	(225)	(2,942)	1,524	5,502
Balance	(2,335)	4,981	(2,335)	4,981
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Balance	(124)
Other comprehensive income before reclassifications, net of tax	56		(68)
Amounts reclassified from accumulated other comprehensive income, net of tax
Net current period other comprehensive income, net of tax	56		(68)
Balance	(68)		(68)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(4,342)	(4,835)	(4,503)	(5,041)
Other comprehensive income before reclassifications, net of tax
Amounts reclassified from accumulated other comprehensive income, net of tax	81	103	242	309
Net current period other comprehensive income, net of tax	81	103	242	309
Balance	(4,261)	(4,732)	(4,261)	(4,732)
AOCI Attributable to Parent [Member]
Balance	(6,576)	3,088	(8,362)	(5,562)
Other comprehensive income before reclassifications, net of tax	(277)	(2,942)	1,348	6,852
Amounts reclassified from accumulated other comprehensive income, net of tax	189	103	350	(1,041)
Net current period other comprehensive income, net of tax	(88)	(2,839)	1,698	5,811
Balance	$ (6,664)	$ 249	$ (6,664)	$ 249