v3.26.1
Segment Information - Schedule of Segment Reporting Information by Segment (Details) - USD ($)
$ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Dec. 31, 2025
Segment Reporting, Profit (Loss) [Abstract]          
Revenues $ 201.9 $ 192.8 $ 555.0 $ 491.5  
Natural gas, propane and electric costs 51.7 50.0 198.6 166.3  
Operations and maintenance expenses 64.7 60.9 140.0 124.3  
Depreciation and amortization 22.9 21.9 44.4 44.4  
Other segment items 9.7 9.7 19.7 19.4  
Operating Income 52.9 50.3 152.3 137.1  
Other income, net 0.5 0.4 0.5 1.0  
Interest charges 18.4 17.8 37.1 35.9  
Income Before Income Taxes 35.0 32.9 115.7 102.2  
Income taxes 9.6 9.0 31.0 27.4  
Net Income 25.4 23.9 84.7 74.8  
Capital expenditures 139.7 99.9 261.6 212.8  
Assets          
Total identifiable assets 4,173.8   4,173.8   $ 3,994.8
Operating revenues, unaffiliated customers          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 201.9 192.8 555.0 491.5  
Intersegment revenues          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 0.0 0.0 0.0 0.0  
Regulated Energy          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 164.3 151.8 413.6 351.4  
Natural gas, propane and electric costs 39.6 34.1 141.2 105.6  
Operations and maintenance expenses 43.8 40.7 95.7 82.4  
Depreciation and amortization 17.3 16.8 33.4 34.4  
Other segment items 8.4 8.4 16.9 16.7  
Operating Income 55.2 51.8 126.4 112.3  
Capital expenditures 113.7 91.5 207.8 187.6  
Assets          
Total identifiable assets 3,587.3   3,587.3   3,425.3
Regulated Energy | Operating revenues, unaffiliated customers          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 163.7 151.4 412.4 350.6  
Regulated Energy | Intersegment revenues          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 0.6 0.4 1.2 0.8  
Unregulated Energy          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 45.2 47.9 158.9 154.6  
Natural gas, propane and electric costs 19.8 22.9 74.9 75.1  
Operations and maintenance expenses 21.0 20.2 44.5 42.0  
Depreciation and amortization 5.6 5.1 11.0 10.0  
Other segment items 1.3 1.2 2.8 2.7  
Operating Income (2.5) (1.5) 25.7 24.8  
Capital expenditures 8.6 7.7 22.1 22.5  
Assets          
Total identifiable assets 477.6   477.6   495.0
Unregulated Energy | Operating revenues, unaffiliated customers          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 38.1 41.4 142.6 140.9  
Unregulated Energy | Intersegment revenues          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 7.1 6.5 16.3 13.7  
Other businesses and eliminations          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues (7.6) (6.9) (17.5) (14.5)  
Natural gas, propane and electric costs (7.7) (7.0) (17.5) (14.4)  
Operations and maintenance expenses (0.1)   (0.2) (0.1)  
Other segment items   0.1      
Operating Income 0.2 0.0 0.2 0.0  
Capital expenditures 17.4 0.7 31.7 2.7  
Assets          
Total identifiable assets 108.9   108.9   $ 74.5
Other businesses and eliminations | Operating revenues, unaffiliated customers          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues 0.1        
Other businesses and eliminations | Intersegment revenues          
Segment Reporting, Profit (Loss) [Abstract]          
Revenues $ (7.7) $ (6.9) $ (17.5) $ (14.5)