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Note 11 - Pension Plan and Other Postretirement Benefits - Asset Allocation Ranges By Asset Class and PBO Funded Status (Details) - Pension Plan [Member] | Dec. 31, 2019
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Equity Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 39.00% |
Equity Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 59.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 34.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 54.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 24.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 44.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Minimum [Member] |  |
Asset allocations | 14.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Maximum [Member] |  |
Asset allocations | 34.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% |
Equity Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 20.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 22.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 42.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 30.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 50.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 40.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 60.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Minimum [Member] |  |
Asset allocations | 53.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Maximum [Member] |  |
Asset allocations | 73.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 70.00% |
Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 100.00% |
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 15.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 15.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 15.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Maximum [Member] |  |
Asset allocations | 10.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [1]
Below Investment Grade Fixed Income Securities [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 10.00% | [1]
Other Asset Categories [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 5.00% | [2]
Other Asset Categories [Member] | Permitted Range, Less Than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 20.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 5.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 85 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 20.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 5.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 90 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 20.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 95% PBO [Member] | Maximum [Member] |  |
Asset allocations | 15.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Minimum [Member] |  |
Asset allocations | 0.00% | [2]
Other Asset Categories [Member] | Permitted Range, Equal to or Greater than 100 Percent PBO [Member] | Maximum [Member] |  |
Asset allocations | 15.00% | [2]
[1] | Includes (but not limited to) High Yield Bond Fund and Emerging Markets Debt funds.
[2] | Other category may include cash, alternatives, and/or other investment strategies that may be classified other than equity or fixed income, such as the Dynamic Asset Allocation fund or the SEI Energy Debt Collective Fund.

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