v3.26.1
Regulation (Details) - USD ($)
$ in Thousands
Mar. 31, 2026
Sep. 30, 2025
Regulatory Asset [Line Items]    
Regulatory assets $ 708,505 $ 608,729
Regulatory Liabilities [Line Items]    
Regulatory liabilities 1,277,855 1,269,648
Regulatory excess deferred taxes    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 152,503 190,274
Regulatory cost of removal obligation    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 647,575 641,019
Deferred gas costs    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 11,999 6,879
APT annual adjustment mechanism    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 128,148 99,393
Pension and postretirement benefit costs    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 292,213 291,351
Other    
Regulatory Liabilities [Line Items]    
Regulatory liabilities 45,417 40,732
Pension and postretirement benefit costs    
Regulatory Asset [Line Items]    
Regulatory assets 4,508 262
Infrastructure mechanisms    
Regulatory Asset [Line Items]    
Regulatory assets 424,630 314,047
Winter Storm Uri incremental costs    
Regulatory Asset [Line Items]    
Regulatory assets 1,843 5,841
Deferred gas costs    
Regulatory Asset [Line Items]    
Regulatory assets 132,354 140,626
Regulatory excess deferred taxes    
Regulatory Asset [Line Items]    
Regulatory assets 49,093 49,793
Recoverable loss on reacquired debt    
Regulatory Asset [Line Items]    
Regulatory assets 2,819 2,903
Deferred pipeline record collection costs    
Regulatory Asset [Line Items]    
Regulatory assets 34,911 39,035
System Safety and Integrity Riders    
Regulatory Asset [Line Items]    
Regulatory assets 41,478 43,625
Other    
Regulatory Asset [Line Items]    
Regulatory assets $ 16,869 $ 12,597