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Note 11 - Pension Plan and Other Postretirement Benefits - Weighted-average Assumptions Used to Determine Net Periodic Benefit Cost (Details) | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Pension Plan [Member] |  |  |
Discount Rate | 4.50% | 3.90% | 4.60%
Long-Term Rate of Return on Plan Assets | 7.25% | 7.50% | 7.50%
Rate of Increase in Future Compensation Level |  |  | 3.00%
Pension Plan [Member] | Participants to Age 39 [Member] |  |  |
Rate of Increase in Future Compensation Level | 4.50% | 4.50% |
Pension Plan [Member] | Participants Age 40 to 49 [Member] |  |  |
Rate of Increase in Future Compensation Level | 3.50% | 3.50% |
Pension Plan [Member] | Participants Age 50 and Older [Member] |  |  |
Rate of Increase in Future Compensation Level | 2.75% | 2.75% |
Executive Survivor and Supplemental Retirement Plan [Member] |  |  |
Discount Rate | 4.46% | 3.85% | 4.60%
Rate of Increase in Future Compensation Level | 3.40% | 2.92% | 3.00%
Other Postretirement Benefits Plan [Member] |  |  |
Discount Rate | 4.44% | 3.81% | 4.46%

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- Definition Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(1) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(3) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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- Definition Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (k)(2) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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