Summary of Significant Accounting Policies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2023 USD ($) mi² segment customer	Mar. 31, 2022 USD ($)	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Significant Accounting Policies [Line Items]
Cash and Cash Equivalents, at Carrying Value	$ 21.0		$ 30.5
Restricted Cash	0.1		0.1
Excise taxes collected	12.0	$ 13.1
Customer receivables	68.3		61.3
Unbilled Revenue	18.2		24.0
Amounts due from partners in jointly owned stations	3.8		3.2
Other	7.0		3.9
Accounts Receivable, Allowance for Credit Loss	(0.6)		(0.5)
Accounts Receivable, Allowance for Credit Loss, Current	0.6	0.2	0.5	$ 0.3
Accounts Receivable, Credit Loss Expense (Reversal)	0.9	(0.1)
Accounts Receivable, Allowance for Credit Loss, Writeoff	(1.1)	(0.2)
Accounts Receivable, Allowance for Credit Loss, Recovery	0.3	0.2
Interest expense	(18.1)	(15.5)
Income Tax Expense (Benefit)	(1.1)	3.7
Net income	(1.2)	(15.4)
Nonoperating Income (Expense)	16.3	15.1
Accumulated other comprehensive income	(2.6)		(2.4)
Other Comprehensive Income (Loss), Net of Tax	(0.2)	0.1
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax	0.0	0.2
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(0.2)	0.1
Contract with Customer, Asset, before Allowance for Credit Loss	86.5		85.3
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	21.1	32.2	30.6	26.7
Accounts Receivable, after Allowance for Credit Loss, Current	96.7		91.9
Other Comprehensive Income (Loss), Cash Flow Hedge, Gain (Loss), Reclassification, after Tax	(0.2)	(0.1)
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income	11.8		12.0
Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Accumulated other comprehensive income	(14.4)		(14.4)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member]
Significant Accounting Policies [Line Items]
Interest expense	(0.2)	(0.2)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Nonoperating Income (Expense)	$ 0.0	0.3
Subsidiaries [Member]
Significant Accounting Policies [Line Items]
Number of reportable segments | segment	1
Cash and Cash Equivalents, at Carrying Value	$ 9.4		19.7
Restricted Cash	$ 0.1		0.1
Approximate number of retail customers | customer	537,000
Service area, square miles | mi²	6,000
Number of Operating Segments | segment	1
Excise taxes collected	$ 12.0	13.1
Customer receivables	67.6		60.6
Unbilled Revenue	18.2		24.0
Amounts due from partners in jointly owned stations	4.5		4.4
Other	6.9		3.8
Accounts Receivable, Allowance for Credit Loss	(0.6)		(0.5)
Accounts Receivable, Allowance for Credit Loss, Current	0.6	0.2	0.5	0.3
Accounts Receivable, Credit Loss Expense (Reversal)	0.9	(0.1)
Accounts Receivable, Allowance for Credit Loss, Writeoff	1.1	0.2
Interest expense	(8.3)	(5.9)
Income Tax Expense (Benefit)	(1.3)	(2.7)
Net income	(9.6)	(16.9)
Nonoperating Income (Expense)	6.8	6.2
Accumulated other comprehensive income	(26.7)		(26.8)
Other Comprehensive Income (Loss), Net of Tax	0.1	0.7
Reclassification from AOCI, Current Period, Net of Tax, Attributable to Parent	0.1
Other Comprehensive Income (Loss), Defined Benefit Plan, Transition Asset (Obligation), Reclassification Adjustment from AOCI, after Tax	0.1	0.7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.1	0.7
Contract with Customer, Asset, before Allowance for Credit Loss	85.8		84.6
Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents	9.5	18.0	19.8	$ 14.5
Accounts Receivable, after Allowance for Credit Loss, Current	96.6		$ 92.3
Subsidiaries [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Change in unfunded pension obligation [Member]
Significant Accounting Policies [Line Items]
Net income	0.1	0.7
Nonoperating Income (Expense)	$ 0.2	$ 0.9