Note 10 - Postretirement Medical Benefits (Details Textual) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Curtailment	$ 351	$ 0
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Prior Service Costs Recognized Due to Curtailment	67
Defined Benefit Plan, Expected Future Employer Contributions, Current Fiscal Year	468
Payment for Other Postretirement Benefits	$ 82
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%