v3.26.3
Business Segments (Narrative) (Details)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Sep. 30, 2025
USD ($)
Sep. 30, 2026
USD ($)
mi²
customer
segment
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Segment Reporting [Line Items]          
Assets, Total $ 3,948.7   $ 3,948.7   $ 3,781.0
Revenues 355.6 $ 294.8 $ 965.4 $ 779.0  
Number of reportable segments | segment     1    
Revenue from external customers          
Segment Reporting [Line Items]          
Revenues 355.6 294.8 $ 965.4 779.0  
Intersegment revenue          
Segment Reporting [Line Items]          
Revenues 0.0 0.0 $ 0.0 0.0  
Subsidiaries [Member]          
Segment Reporting [Line Items]          
Approximate number of retail customers | customer     546,000    
Service area, square miles | mi²     6,000    
Assets, Total 3,883.5   $ 3,883.5   3,730.8
Utility [Member]          
Segment Reporting [Line Items]          
Revenues 353.2 292.7 958.3 772.4  
Operating Segments [Member] | Utility [Member]          
Segment Reporting [Line Items]          
Revenues 353.2 292.7 958.3 772.4  
Operating Segments [Member] | Utility [Member] | Revenue from external customers          
Segment Reporting [Line Items]          
Revenues 353.1 292.3 958.2 771.5  
Operating Segments [Member] | Utility [Member] | Intersegment revenue          
Segment Reporting [Line Items]          
Revenues 0.1 0.4 0.1 0.9  
Corporate, Non-Segment [Member]          
Segment Reporting [Line Items]          
Assets, Total 65.2   65.2   $ 50.2
Revenues 3.9 3.6 11.4 11.0  
Corporate, Non-Segment [Member] | Revenue from external customers          
Segment Reporting [Line Items]          
Revenues 2.8 2.5 8.1 7.5  
Corporate, Non-Segment [Member] | Intersegment revenue          
Segment Reporting [Line Items]          
Revenues 1.1 1.1 3.3 3.5  
Intersegment Eliminations          
Segment Reporting [Line Items]          
Revenues (1.5) (1.5) (4.3) (4.4)  
Intersegment Eliminations | Revenue from external customers          
Segment Reporting [Line Items]          
Revenues (0.3) 0.0 (0.9) 0.0  
Intersegment Eliminations | Intersegment revenue          
Segment Reporting [Line Items]          
Revenues $ (1.2) $ (1.5) $ (3.4) $ (4.4)