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Organization, Summary of Significant Accounting Policies and Recent Developments (Narrative) (Details) - USD ($) $ in Millions | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items] |  |  |
Percent voting interest | 50.00% |  |
Percent of operating revenues | 91.00% |  |
Percent of total assets | 99.00% |  |
Allowance for doubtful accounts | $ 1.4 | $ 1.0 |
Bad debt expense | 1.0 | 0.8 | $ 0.5
Write-offs | 0.6 | $ 0.7 | 0.5
Operations and Maintenance expense and Other Income (Expense), net |  |  | $ 0.8
Right-of-use asset | 6.7 |  |
Lease liability | 7.1 |  |
Regulatory assets | $ 0.4 |  |
Minimum [Member] |  |  |
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items] |  |  |
Estimated useful lives of non-regulated fixed assets | 3 years |  |
Maximum [Member] |  |  |
Organization, Summary Of Significant Accounting Policies And Recent Developments [Line Items] |  |  |
Estimated useful lives of non-regulated fixed assets | 42 years |  |

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