v3.26.3
Business Segments (Narrative) (Details)
$ in Millions
3 Months Ended 9 Months Ended
Sep. 30, 2026
USD ($)
Jun. 30, 2026
USD ($)
Mar. 31, 2026
USD ($)
Sep. 30, 2025
USD ($)
Jun. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
Sep. 30, 2026
USD ($)
mi²
segment
customer
Sep. 30, 2025
USD ($)
Dec. 31, 2025
USD ($)
Segment Reporting [Line Items]                  
Number of Operating Segments | segment             1    
Approximate number of retail customers | customer             546,000    
Service area, square miles | mi²             6,000    
Total assets $ 3,883.5           $ 3,883.5   $ 3,730.8
Revenues 353.2     $ 292.7     958.3 $ 772.4  
Purchased power 128.6     113.6     340.4 290.9  
Operation and maintenance 84.7     70.4     241.4 199.1  
Depreciation and amortization 30.0     29.4     92.4 87.2  
Taxes other than income taxes 40.5     36.3     117.6 100.2  
Interest expense 14.9     14.6     45.1 43.0  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.5     27.8     122.2 49.7  
Income Tax Expense (Benefit) 12.5     10.9     27.5 16.6  
Net Income (Loss) Attributable to Parent, Total 42.0 $ 10.5 $ 42.2 16.9 $ 5.5 $ 10.7 94.7 33.1  
Operating Segments [Member]                  
Segment Reporting [Line Items]                  
Revenues             958.3    
Purchased power             340.4    
Operation and maintenance             241.4    
Depreciation and amortization             92.4    
Taxes other than income taxes             117.6    
Interest expense             45.1    
Segment Reporting, Other Segment Item, Amount             (0.8)    
Operating Segments [Member] | Utility [Member]                  
Segment Reporting [Line Items]                  
Revenues 353.2     292.7       772.4  
Purchased power 128.6     113.6       290.9  
Operation and maintenance 84.7     70.4       199.1  
Depreciation and amortization 30.0     29.4       87.2  
Taxes other than income taxes 40.5     36.3       100.2  
Interest expense 14.9     14.6       43.0  
Segment Reporting, Other Segment Item, Amount 0.0     0.6       2.3  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 54.5     27.8     122.2 49.7  
Income Tax Expense (Benefit) 12.5     10.9     27.5 16.6  
Net Income (Loss) Attributable to Parent, Total 42.0     16.9     94.7 33.1  
Segment Reporting, Long-Lived Asset, Expenditure for Addition $ 148.2     $ 98.6     $ 365.2 $ 256.1