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Note 9 - Pensions and Other Postretirement Benefits (Details Textual) - USD ($) $ in Thousands | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement | $ 0 | $ 2,900 | $ 4,000
Unrecognized Actuarial Gain (Loss) in Excess of Benefit Obligation, Percentage | 10.00% |  |
Defined Benefit Plan, Expected Future Employer Contributions, Next Fiscal Year | $ 2,000 |  |
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components | 300 |  |
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation | 2,300 |  |
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components | 200 |  |
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation | 2,100 |  |
One Percentage Point Change in Assumed Rate of Return [Member] |  |  |
Defined Benefit Plan Effect On Pension Expense | 700 |  |
One Percentage Point Increase in Discount Rate [Member] |  |  |
Defined Benefit Plan Effect On Pension Expense | 1,300 |  |
One Percentage Point Decrease in Discount Rate [Member] |  |  |
Defined Benefit Plan Effect On Pension Expense | $ 1,500 |  |
Defined Benefit Plan, Equity Securities [Member] | Minimum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 8.00% |  |
Defined Benefit Plan, Equity Securities [Member] | Maximum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 28.00% |  |
Fixed Income Securities [Member] | Minimum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 70.00% |  |
Fixed Income Securities [Member] | Maximum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 90.00% |  |
Alternative Investments [Member] | Minimum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 0.00% |  |
Alternative Investments [Member] | Maximum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 4.00% |  |
Cash and Cash Equivalents [Member] | Minimum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 0.00% |  |
Cash and Cash Equivalents [Member] | Maximum [Member] |  |  |
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage | 10.00% |  |
Pension Plan [Member] |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount |  |  | 1,900
Pension Plan [Member] |  |  |
Defined Contribution Plan, Employer Discretionary Contribution Amount | $ 2,300 | 2,200 |
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement |  | $ (2,852) | $ (4,031)
Postretirement Health Coverage [Member] |  |  |
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate | 5.00% | 0.00% |

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