v3.26.1
Revenue and Accounts Receivable - Schedule of Disaggregation of Revenue (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Disaggregation of Revenue [Line Items]        
Total operating revenues $ 879,059 $ 838,774 $ 4,184,046 $ 3,965,275
Distribution        
Disaggregation of Revenue [Line Items]        
Total operating revenues 773,909 766,380 3,908,869 3,756,691
Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Total operating revenues 105,150 72,394 275,177 208,584
Operating Segments        
Disaggregation of Revenue [Line Items]        
Total operating revenues 1,107,711 1,039,520 4,820,139 4,545,772
Operating Segments | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 752,247 762,378 3,732,032 3,699,612
Alternative revenue program revenues 18,588 1,438 167,599 48,657
Other revenues 3,823 3,316 11,533 10,726
Total operating revenues 774,658 767,132 3,911,164 3,758,995
Operating Segments | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 406,263 288,759 1,048,427 828,225
Alternative revenue program revenues (73,210) (16,371) (139,452) (41,448)
Other revenues 0 0 0 0
Total operating revenues 333,053 272,388 908,975 786,777
Operating Segments | Gas sales revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 709,738 723,144 3,597,383 3,573,055
Operating Segments | Gas sales revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Operating Segments | Transportation revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 39,498 35,908 125,339 115,987
Operating Segments | Transportation revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 395,186 284,103 1,031,369 816,646
Operating Segments | Miscellaneous revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 3,011 3,326 9,310 10,570
Operating Segments | Miscellaneous revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 11,077 4,656 17,058 11,579
Operating Segments | Residential | Gas sales revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 462,720 473,478 2,462,924 2,475,219
Operating Segments | Residential | Gas sales revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Operating Segments | Commercial | Gas sales revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 214,797 213,377 999,363 959,539
Operating Segments | Commercial | Gas sales revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Operating Segments | Industrial | Gas sales revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 26,464 27,369 103,804 92,575
Operating Segments | Industrial | Gas sales revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 0 0 0 0
Operating Segments | Public authority and other | Gas sales revenues | Distribution        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers 5,757 8,920 31,292 45,722
Operating Segments | Public authority and other | Gas sales revenues | Pipeline and Storage        
Disaggregation of Revenue [Line Items]        
Revenues from contracts with customers $ 0 $ 0 $ 0 $ 0