Business Segments (Segment Financial Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Segment Reporting Information [Line Items]
REVENUE	$ 1,070.6	$ 876.5	$ 861.0
Purchased power	394.3	316.4	346.9
Operation and maintenance	281.1	259.1	232.1
Depreciation and amortization	119.4	95.2	82.1
Taxes other than income taxes	137.3	113.5	100.8
Interest expense	82.4	85.0	63.6
Other segment items (a)	0.2	(3.5)	(6.8)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	55.9	10.8	42.3
Income Tax Expense (Benefit)	22.9	(3.0)	6.6
Net income (loss)	33.0	13.8	35.7
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	387.2	549.5	387.9
Total assets (end of year)	3,781.0	3,417.4	2,906.2
Payments to Acquire Productive Assets	(387.2)	(549.5)	(387.9)
Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	0.0	0.0	0.0
Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	1,070.6	876.5	861.0
Utility [Member]
Segment Reporting Information [Line Items]
REVENUE	1,061.8	867.6	852.0
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
REVENUE	1,061.8	867.6	852.0
Purchased power	393.4	315.4	346.0
Operation and maintenance	278.1	258.3	229.8
Depreciation and amortization	117.5	93.4	80.7
Taxes other than income taxes	137.0	113.4	100.6
Interest expense	57.8	48.2	25.8
Other segment items (a)	3.3	(1.2)	(5.8)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	74.7	40.1	74.9
Income Tax Expense (Benefit)	24.1	3.2	13.5
Net income (loss)	50.6	36.9	61.4
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	385.7	547.9	384.3
Total assets (end of year)	3,730.8	3,355.2	2,871.0
Operating Segments [Member] | Utility [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	1.1	0.9	0.7
Operating Segments [Member] | Utility [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	1,060.7	866.7	851.3
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
REVENUE	14.5	14.7	14.1
Purchased power	2.0	1.9	1.6
Operation and maintenance	7.6	5.7	6.7
Depreciation and amortization	1.9	1.8	1.4
Taxes other than income taxes	0.3	0.1	0.2
Interest expense	24.6	36.6	39.2
Other segment items (a)	(3.1)	(2.1)	(2.4)
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	(18.8)	(29.3)	(32.6)
Income Tax Expense (Benefit)	(1.2)	(6.2)	(6.9)
Net income (loss)	(17.6)	(23.1)	(25.7)
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	1.5	1.6	3.6
Total assets (end of year)	50.2	62.2	35.2
Corporate, Non-Segment [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	4.6	4.9	4.4
Corporate, Non-Segment [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	9.9	9.8	9.7
Intersegment Eliminations
Segment Reporting Information [Line Items]
REVENUE	(5.7)	(5.8)	(5.1)
Purchased power	(1.1)	(0.9)	(0.7)
Operation and maintenance	(4.6)	(4.9)	(4.4)
Depreciation and amortization	0.0	0.0	0.0
Taxes other than income taxes	0.0	0.0	0.0
Interest expense	0.0	0.2	(1.4)
Other segment items (a)	0.0	(0.2)	1.4
Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest	0.0	0.0	0.0
Income Tax Expense (Benefit)	0.0	0.0	0.0
Net income (loss)	0.0	0.0	0.0
Segment Reporting Information, Income (Loss) before Income Taxes [Abstract]
Segment, Expenditure, Addition to Long-Lived Assets	0.0	0.0	0.0
Intersegment Eliminations | Intersegment revenue
Segment Reporting Information [Line Items]
REVENUE	(5.7)	(5.8)	(5.1)
Intersegment Eliminations | Revenue from external customers
Segment Reporting Information [Line Items]
REVENUE	$ 0.0	$ 0.0	$ 0.0