Note 2 - Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Balance	$ 184,066	$ 175,698	$ 172,929
Other comprehensive income (loss)	475	(6,190)	(2,093)
Adoption of Accounting Standards Update 2018-02
Balance	193,353	184,066	175,698
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Balance	(3,363)	3,219
Other comprehensive income (loss) before reclassifications	489	(3,983)
Amounts reclassified from accumulated other comprehensive income	(13)	(2,599)
Other comprehensive income (loss)	476	(6,582)
Adoption of Accounting Standards Update 2018-02	(623)
Balance	(3,510)	(3,363)	3,219
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Balance	(45)	(437)
Other comprehensive income (loss) before reclassifications	(53)	356
Amounts reclassified from accumulated other comprehensive income	52	36
Other comprehensive income (loss)	(1)	392
Adoption of Accounting Standards Update 2018-02	(10)
Balance	(56)	(45)	(437)
AOCI Attributable to Parent [Member]
Balance	(3,408)	2,782	4,875
Other comprehensive income (loss) before reclassifications	436	(3,627)
Amounts reclassified from accumulated other comprehensive income	39	(2,563)
Other comprehensive income (loss)	475	(6,190)	(2,093)
Adoption of Accounting Standards Update 2018-02	(633)
Balance	$ (3,566)	$ (3,408)	$ 2,782