Note 12 - Pension and Other Postretirement Benefit Plans - The Resulting Net Periodic Postretirement Expense Consisted of the Following Components for the Year (Details) - Other Postretirement Benefits Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Service cost	$ 316	$ 359	$ 382
Interest cost	305	320	300
Amortization of unrecognized loss		47	119
Amortization of past service credit	(85)	(85)	(85)
Net pension expense	536	641	716
Current year actuarial (gain) loss	587	(613)	(715)
Amortization of actuarial loss		(47)	(119)
Amortization of prior service credit	(85)	(85)	(85)
Total recognized in other comprehensive income	672	(575)	(749)
Total recognized in net pension cost (benefit) and other comprehensive loss	$ 1,208	$ 66	$ (33)