Note 12 - Pension and Other Postretirement Benefits - The Components of the Net Pension Expense for the Retirement Plan (Details) - Retirement Plan [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest cost	$ 864	$ 902	$ 889
Amortization of unrecognized loss	697	809	1,112
Expected return on plan assets	(1,392)	(1,394)	(1,400)
Net pension expense	169	317	601
Current year actuarial (gain) loss	(1,192)	275	(237)
Amortization of actuarial loss	(697)	(809)	(1,112)
Total recognized in other comprehensive income	(1,889)	(534)	(1,349)
Total recognized in net pension cost (benefit) and other comprehensive loss	$ (1,720)	$ (217)	$ (748)