v3.26.1
Business Segment Information (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2026
Sep. 30, 2025
Mar. 31, 2025
Sep. 30, 2024
Segment Reporting [Line Items]        
Income Tax Expense (Benefit) $ 34,222   $ 35,940  
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest 48,759   18,548  
Net Income (Loss) Attributable to Parent   $ 110,121   $ 101,143
Segment Reporting, Long-Lived Asset, Expenditure for Addition 232,525   147,116  
UTILITY OPERATING REVENUES 521,920   477,700  
Fuel Costs 111,455   106,509  
Cost of Goods and Services Sold 34,883   35,530  
Utilities Operating Expense, Maintenance and Operations 141,801   142,608  
Depreciation and amortization 94,791   85,605  
Taxes other than income taxes 11,622   9,072  
Allowance for equity funds used during construction (1,590)   (669)  
Interest Expense 46,372   43,991  
Segment Reporting, Other Segment Item, Amount (395)   566  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 82,981   54,488  
Other Segments [Member]        
Segment Reporting [Line Items]        
Income Tax Expense (Benefit) (1,649)   (252)  
Net Income (Loss) Attributable to Parent (8,745)   (10,337)  
Utilities Operating Expense, Maintenance and Operations 67   122  
Interest Expense 10,495   10,448  
Segment Reporting, Other Segment Item, Amount (168)   19  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest (10,394)   (10,589)  
Corporate Segment        
Segment Reporting [Line Items]        
Income Tax Expense (Benefit) 35,871   36,192  
Net Income (Loss) Attributable to Parent 57,504   28,885  
Segment Reporting, Long-Lived Asset, Expenditure for Addition 232,525   147,116  
UTILITY OPERATING REVENUES 521,920   477,700  
Fuel Costs 111,455   106,509  
Cost of Goods and Services Sold 34,883   35,530  
Utilities Operating Expense, Maintenance and Operations 141,734   142,486  
Depreciation and amortization 94,791   85,605  
Taxes other than income taxes 11,622   9,072  
Allowance for equity funds used during construction (1,590)   (669)  
Interest Expense 35,877   33,543  
Segment Reporting, Other Segment Item, Amount (227)   547  
Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest 93,375   65,077  
Electricity [Member]        
Segment Reporting [Line Items]        
UTILITY OPERATING REVENUES $ 521,920   $ 477,700