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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
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%

X

- 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

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