Note 9 - Retirement Plans and Postretirement Benefit Plans - Postretirement Benefit Expense (Details) - USD ($) $ in Thousands |
12 Months Ended | ||
|---|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Service cost | $ 128 | $ 173 | $ 135 |
| Interest cost | 142 | 143 | 144 |
| Prior service costs | 2 | ||
| Amortization of gains | 27 | 1 | |
| Net postretirement benefit expense | $ 270 | $ 343 | $ 282 |