Note 13 - Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Balance	$ 513,853	$ 473,067
Total other comprehensive income, net of tax	1,228	6,873
Balance	525,402	487,779
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	(3,859)	(521)
Other comprehensive income before reclassifications, net of tax	1,148	6,770
Amounts reclassified from accumulated other comprehensive income, net of tax
Total other comprehensive income, net of tax	1,148	6,770
Balance	(2,711)	6,249
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(4,503)	(5,041)
Other comprehensive income before reclassifications, net of tax
Amounts reclassified from accumulated other comprehensive income, net of tax	80	103
Total other comprehensive income, net of tax	80	103
Balance	(4,423)	(4,938)
AOCI Attributable to Parent [Member]
Balance	(8,362)	(5,562)
Other comprehensive income before reclassifications, net of tax	1,148	6,770
Amounts reclassified from accumulated other comprehensive income, net of tax	80	103
Total other comprehensive income, net of tax	1,228	6,873
Balance	$ (7,134)	$ 1,311