Business Segments (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2025 USD ($)	Jun. 30, 2024 USD ($)	Jun. 30, 2025 USD ($) mi² segment customer	Jun. 30, 2024 USD ($)	Dec. 31, 2024 USD ($)
Segment Reporting Information [Line Items]
Number of Operating Segments | segment			1
Assets, Total	$ 3,521.0		$ 3,521.0		$ 3,417.4
Revenues	229.9	$ 209.2	484.2	$ 435.6
Revenue from external customers
Segment Reporting Information [Line Items]
Revenues	229.9	209.2	484.2	435.6
Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	$ 0.0	0.0
Subsidiaries [Member]
Segment Reporting Information [Line Items]
Approximate number of retail customers | customer			543,000
Service area, square miles | mi²			6,000
Assets, Total	3,462.6		$ 3,462.6		3,355.2
Utility [Member]
Segment Reporting Information [Line Items]
Revenues	227.6	206.9	479.7	431.2
Corporate and Other
Segment Reporting Information [Line Items]
Revenues	3.7	3.8	7.4	7.3
Operating Segments [Member] | Utility [Member]
Segment Reporting Information [Line Items]
Revenues	227.6	206.9	479.7	431.2
Operating Segments [Member] | Utility [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
Revenues	227.4	206.7	479.2	430.8
Operating Segments [Member] | Utility [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	0.2	0.2	0.5	0.4
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Assets, Total	58.4		58.4		$ 62.2
Revenues	3.7	3.8	7.4	7.3
Corporate, Non-Segment [Member] | Revenue from external customers
Segment Reporting Information [Line Items]
Revenues	2.5	2.5	5.0	4.8
Corporate, Non-Segment [Member] | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	1.2	1.3	2.4	2.5
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenues	(1.4)	(1.5)	(2.9)	(2.9)
Intersegment Eliminations | Revenue from external customers
Segment Reporting Information [Line Items]
Revenues	0.0	0.0	0.0	0.0
Intersegment Eliminations | Intersegment revenue
Segment Reporting Information [Line Items]
Revenues	$ (1.4)	$ (1.5)	$ (2.9)	$ (2.9)