v3.26.1
Regulation (Details) - USD ($)
$ in Thousands
Jun. 30, 2026
Sep. 30, 2025
Regulatory Asset [Line Items]    
Regulatory assets $ 741,631 $ 608,729
Regulatory Liabilities [Line Items]    
Regulatory liabilities 1,294,073 1,269,648
Regulatory excess deferred taxes    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 134,694 190,274
Regulatory cost of removal obligation    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 645,942 641,019
Deferred gas costs    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 6,844 6,879
APT annual adjustment mechanism    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 182,546 99,393
Pension and postretirement benefit costs    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 289,505 291,351
Other    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 34,542 40,732
Pension and postretirement benefit costs    
Regulatory Asset [Line Items]    
Regulatory assets 3,857 262
Infrastructure mechanisms    
Regulatory Asset [Line Items]    
Regulatory assets 425,281 314,047
Winter Storm Uri incremental costs    
Regulatory Asset [Line Items]    
Regulatory assets 1,141 5,841
Deferred gas costs    
Regulatory Asset [Line Items]    
Regulatory assets 156,975 140,626
Regulatory excess deferred taxes    
Regulatory Asset [Line Items]    
Regulatory assets 48,718 49,793
Recoverable loss on reacquired debt    
Regulatory Asset [Line Items]    
Regulatory assets 2,777 2,903
Deferred pipeline record collection costs    
Regulatory Asset [Line Items]    
Regulatory assets 35,642 39,035
System Safety and Integrity Riders    
Regulatory Asset [Line Items]    
Regulatory assets 48,801 43,625
Other    
Regulatory Asset [Line Items]    
Regulatory assets $ 18,439 $ 12,597