v3.26.1
Business Segments (Segment Financial Information) (Details) - USD ($)
$ in Millions
 3 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Dec. 31, 2025
Segment Reporting [Line Items]      
Revenues $ 338.7 $ 252.1  
Depreciation and amortization 31.3 28.8  
Interest expense 15.4 14.7  
Total assets 3,717.3   $ 3,730.8
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.4 12.4  
Purchased power 119.0 94.8  
Operation and maintenance 80.2 63.9  
Taxes other than income taxes 38.2 36.2  
Other Nonoperating Income (Expense) (0.2) (1.3)  
Income Tax Expense (Benefit) 12.2 1.7  
Net Income (Loss) Attributable to Parent 42.2 10.7  
Utility [Member]      
Segment Reporting [Line Items]      
Income Tax Expense (Benefit) 12.2    
Operating Segments [Member]      
Segment Reporting [Line Items]      
Revenues 338.7    
Depreciation and amortization 31.3    
Interest expense 15.4    
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.4    
Purchased power 119.0    
Operation and maintenance 80.2    
Taxes other than income taxes 38.2    
Segment Reporting, Other Segment Item, Amount 0.2    
Operating Segments [Member] | Utility [Member]      
Segment Reporting [Line Items]      
Revenues   252.1  
Depreciation and amortization   28.8  
Interest expense   14.7  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest   12.4  
Purchased power   94.8  
Operation and maintenance   63.9  
Taxes other than income taxes   36.2  
Income Tax Expense (Benefit)   1.7  
Net Income (Loss) Attributable to Parent 42.2 10.7  
Segment Reporting, Other Segment Item, Amount   1.3  
Segment Reporting, Long-Lived Asset, Expenditure for Addition $ 114.1 $ 85.3