Organization, Summary of Significant Accounting Policies and Recent Developments (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
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	$ 2.1	$ 1.4
Bad debt expense	1.1	1.0	$ 0.8
Write-offs	0.5	$ 0.6	$ 0.7
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