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Note 11 - Pension Plan and Other Postretirement Benefits - Pension Plan Asset Allocations by Asset Category (Details) - Pension Plan [Member] | Dec. 31, 2019 | Dec. 31, 2018
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Defined Benefit Plan, Actual Plan Asset Allocations | 100.00% | 100.00%
Mixed Equities Fund [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 20.40% |
Large Capitalization Equity Securities [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 11.30% | 17.50%
International Equity Securities [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 9.30% | 17.00%
Emerging Markets Equity Funds [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 4.20% | 3.40%
Small and Mid Capitalization Equity Securities [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 4.10% | 6.70%
SEI Dynamic Asset Allocation Fund [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 3.10% | 4.00%
Equity Securities [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 52.40% | 48.60%
Fixed-income Securities and Cash [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 44.70% | 47.10%
Other - SEI Energy Debt Collective Fund [Member] |  |
Defined Benefit Plan, Actual Plan Asset Allocations | 2.90% | 4.30%

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- Definition Percentage of actual investment allocation to total plan assets. Includes, but is not limited to, percentage on weighted-average basis if more than one plan. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (d)(i) -URI http://asc.fasb.org/extlink&oid=118255775&loc=d3e1928-114920 + Details
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