Note 17 - Components of Accumulated Other Comprehensive Income (Loss) - Components of Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance	$ 178,263	$ 172,114	$ 166,303
Unrealized holding gain (loss) on available for sale securities, net of tax	546	(800)	(1,064)
Net pension gain (loss) arising during the period, net of tax	213	271	(1,108)
Less amortization of prior service cost included in net periodic pension cost, net of tax	(71)	(72)	(72)
Reclassification of stranded tax effects from change in tax rate
Balance	184,896	178,263	172,114
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	(3,588)	(2,667)	(1,582)
Unrealized holding gain (loss) on available for sale securities, net of tax	546	(800)	(1,064)
Reclassification adjustment, net of tax	(6)	(121)	(21)
Net pension gain (loss) arising during the period, net of tax
Less amortization of prior service cost included in net periodic pension cost, net of tax
Reclassification of stranded tax effects from change in tax rate	(656)
Balance	(3,704)	(3,588)	(2,667)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(5,071)	(5,270)	(4,090)
Unrealized holding gain (loss) on available for sale securities, net of tax	0
Reclassification adjustment, net of tax		0	0
Net pension gain (loss) arising during the period, net of tax	213	271	(1,108)
Less amortization of prior service cost included in net periodic pension cost, net of tax	(71)	(72)	(72)
Reclassification of stranded tax effects from change in tax rate	(1,062)
Balance	(5,991)	(5,071)	(5,270)
AOCI Attributable to Parent [Member]
Balance	(8,659)	(7,937)	(5,672)
Unrealized holding gain (loss) on available for sale securities, net of tax	546	(800)	(1,064)
Reclassification adjustment, net of tax	(6)	(121)	(21)
Net pension gain (loss) arising during the period, net of tax	213	271	(1,108)
Less amortization of prior service cost included in net periodic pension cost, net of tax	(71)	(72)	(72)
Reclassification of stranded tax effects from change in tax rate	(1,718)
Balance	$ (9,695)	$ (8,659)	$ (7,937)