Note 13 - Postretirement Medical Benefits - Net Periodic Benefit Cost (Details) - Postretirement Health Coverage [Member] - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Service cost	$ 637	$ 739
Interest cost	683	649
Recognized prior service cost	50	51
Amortization of net actuarial loss		42
Net periodic benefit cost	$ 1,370	$ 1,481
Discount rate used to determine net periodic benefit cost	4.34%	3.92%
Discount rate used to determine benefit obligation as of year end	4.12%	4.34%
Retiree participation rate (Plan 1)	100.00%	100.00%
Retiree participation rate (Plan 2)	72.00%	72.00%