Note 7 - Employee Benefits Plans - Amount Recognized in the Consolidated Balance Sheet (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Compensation Plan [Member]
Current liabilities	$ (404)	$ (450)
Noncurrent liabilities	(4,101)	(4,219)
Total	(4,505)	(4,669)
Supplemental Employee Retirement Plan [Member]
Current liabilities	(154)	(155)
Noncurrent liabilities	(1,701)	(1,724)
Total	(1,855)	(1,879)
Other Postretirement Benefits Plan [Member]
Current liabilities	(88)	(88)
Noncurrent liabilities	(605)	(622)
Total	$ (693)	$ (710)