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Note 11 - Pension Plan and Other Postretirement Benefits - Pension Fund Assets Measured at Fair Value (Details) - Pension Plan [Member] - USD ($) $ in Thousands | Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
--- | --- | --- | ---
Fair Value of Plan Assets | $ 329,781 | $ 269,783 | $ 285,319
Fair Value, Inputs, Level 1 [Member] |  |  |
Fair Value of Plan Assets | 320,241 | 258,307 |
Fair Value, Inputs, Level 1 [Member] | Mixed Equities Fund [Member] |  |  |
Fair Value of Plan Assets | 67,184 | 0 |
Fair Value, Inputs, Level 1 [Member] | Large Capitalization Equity Securities [Member] |  |  |
Fair Value of Plan Assets | 37,357 | 47,198 |
Fair Value, Inputs, Level 1 [Member] | International Equity Securities [Member] |  |  |
Fair Value of Plan Assets | 30,653 | 45,912 |
Fair Value, Inputs, Level 1 [Member] | Small and Mid Capitalization Equity Securities [Member] |  |  |
Fair Value of Plan Assets | 13,447 | 17,971 |
Fair Value, Inputs, Level 1 [Member] | SEI Dynamic Asset Allocation Fund [Member] |  |  |
Fair Value of Plan Assets | 10,168 | 10,929 |
Fair Value, Inputs, Level 1 [Member] | Emerging Markets Equity Funds [Member] |  |  |
Fair Value of Plan Assets | 13,792 | 9,197 |
Fair Value, Inputs, Level 1 [Member] | Fixed Income Securities [Member] |  |  |
Fair Value of Plan Assets | 147,639 | 127,098 |
Fair Value, Inputs, Level 1 [Member] | Cash Management Money Market Fund [Member] |  |  |
Fair Value of Plan Assets | $ 1 | $ 2 |

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