Note 10 - Pension Plan and Other Postretirement Benefits (Details Textual) - Pension Plan [Member] - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Defined Benefit Plan, Minimum Funding Requirement		$ 0
Defined Benefit Plan, Plan Assets, Contributions by Employer	$ 20,000