Note 13 - Postretirement Medical Benefits (Details Textual) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Number of Postretirement Medical and Dental Plan Participants	37
Defined Benefit Plan, Contributions by Employer	$ 309	$ 289
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	$ 416
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	6.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Year Two	6.00%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed, Year Three	5.50%
Plan 2 [Member]
Employee Service Requirement	20 years
Employee Age Requirement	55 years
Contributions Plan 2	50.00%
Plan 1 [Member]
Company Contributions Plan 1	100.00%
Medical [Member]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.75%
Dental [Member]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%