v3.26.1
Capitalization (Narrative) (Details)
$ / shares in Units, $ in Thousands
 9 Months Ended
Jun. 11, 2026
USD ($)
Jun. 10, 2026
USD ($)
Dec. 17, 2025
$ / shares
shares
Jun. 30, 2026
USD ($)
$ / shares
shares
Jun. 30, 2025
USD ($)
Mar. 27, 2026
USD ($)
lender
Sep. 30, 2025
USD ($)
$ / shares
Feb. 14, 2024
USD ($)
lender
Debt Instrument [Line Items]                
Common stock, par value (in dollars per share) | $ / shares       $ 1     $ 1  
Net proceeds from common stock sale       $ 338,396 $ 0      
Current portion of long-term debt       0     $ 300,000  
Premiums Paid on Early Redemption of Debt       (413) $ (2,385)      
Unamortized Debt Expense       $ 5,821     6,236  
4.75% Notes Due May 15, 2029                
Debt Instrument [Line Items]                
Coupon Rate   4.75%            
Debt instrument, redemption price, percentage   101.00%            
Maximum interest rate adjustment   2.00%            
Long-term debt, face amount   $ 500,000            
4.75% Notes Due May 15, 2029 | Maximum                
Debt Instrument [Line Items]                
Coupon Rate   6.75%            
5.05% Notes Due October 15, 2031                
Debt Instrument [Line Items]                
Coupon Rate   5.05%            
Debt instrument, redemption price, percentage   101.00%            
Maximum interest rate adjustment   2.00%            
Long-term debt, face amount   $ 500,000            
5.05% Notes Due October 15, 2031 | Maximum                
Debt Instrument [Line Items]                
Coupon Rate   7.05%            
5.50% Notes Due May 15, 2036                
Debt Instrument [Line Items]                
Coupon Rate   5.50%            
Debt instrument, redemption price, percentage   101.00%            
Maximum interest rate adjustment   2.00%            
Long-term debt, face amount   $ 500,000            
5.50% Notes Due May 15, 2036 | Maximum                
Debt Instrument [Line Items]                
Coupon Rate   7.50%            
5.50% Notes Due June 2026                
Debt Instrument [Line Items]                
Coupon Rate 5.50%              
Long-term debt, face amount $ 300,000              
Debt instrument redeemed 301,200              
5.50% Notes Due June 2026 | Integrated Upstream and Gathering                
Debt Instrument [Line Items]                
Premiums Paid on Early Redemption of Debt 400              
5.50% Notes Due June 2026 | Pipeline and Storage                
Debt Instrument [Line Items]                
Unamortized Debt Expense 200              
5.50% Notes Due June 2026 | Utility                
Debt Instrument [Line Items]                
Unamortized Debt Expense $ 600              
Credit Agreement                
Debt Instrument [Line Items]                
Number of lenders | lender           12    
Maximum borrowing capacity           $ 1,300,000    
Term Loan Agreement                
Debt Instrument [Line Items]                
Number of lenders | lender               6
Maximum borrowing capacity               $ 300,000
Rate adjustment to SOFR       0.0010        
Spread on variable rate       1.375%        
Current portion of long-term debt             $ 300,000  
Sale of Common Stock                
Debt Instrument [Line Items]                
Common stock issued from sale of common stock (in shares) | shares     4,402,513 4,402,513        
Common stock, par value (in dollars per share) | $ / shares     $ 1.00          
Per share or per unit amount of equity securities issued (in dollars per share) | $ / shares     $ 79.50          
Net proceeds from common stock sale       $ 338,400