Note 3 - Accumulated Other Comprehensive Income - Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Beginning balance			$ 184,066	$ 175,698
Net current-period other comprehensive income	$ 1,339	$ 1,673	2,352	4,315
Ending balance	192,876	188,826	192,876	188,826
Accumulated Net Investment Gain (Loss) Attributable to Parent [Member]
Beginning balance	(2,409)	5,852	(3,363)	3,219
Other comprehensive income before reclassifications	1,329	1,749	2,277	4,436
Amounts reclassified from accumulated other comprehensive income	1	(85)	7	(139)
Net current-period other comprehensive income	1,330	1,664	2,284	4,297
Ending balance	(1,079)	7,516	(1,079)	7,516
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Beginning balance	14	(428)	(45)	(437)
Other comprehensive income before reclassifications	8	0	17	0
Amounts reclassified from accumulated other comprehensive income	1	9	51	18
Net current-period other comprehensive income	9	9	68	18
Ending balance	23	(419)	23	(419)
AOCI Attributable to Parent [Member]
Beginning balance	(2,395)	5,424	(3,408)	2,782
Other comprehensive income before reclassifications	1,337	1,749	2,294	4,436
Amounts reclassified from accumulated other comprehensive income	2	(76)	58	(121)
Net current-period other comprehensive income	1,339	1,673	2,352	4,315
Ending balance	$ (1,056)	$ 7,097	$ (1,056)	$ 7,097