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% |