v3.26.1
Business Segment Information - (Schedule of Information By Segment) (Details) - USD ($)
$ in Thousands
 3 Months Ended 9 Months Ended
Jun. 30, 2026
Jun. 30, 2025
Jun. 30, 2026
Jun. 30, 2025
Sep. 30, 2025
Segment Reporting [Line Items]          
Revenues From External Customers [1] $ 537,497 $ 531,830 $ 2,047,377 $ 1,811,262  
Intersegment Revenues 0 0 0 0  
Total Revenues 537,497 531,830 2,047,377 1,811,262  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 17,424 18,543 55,177 56,599  
Lease Operating Expense [2] 15,315 11,263 48,179 31,197  
Gathering Operation and Maintenance Expense [2] 13,526 7,800 37,581 23,566  
All Other Operation and Maintenance Expense [2] 108,874 95,398 315,975 287,238  
Purchased Gas [2] 29,878 27,986 323,335 228,661  
Depreciation, Depletion and Amortization [2] 121,058 116,408 362,412 337,055  
Impairment of Assets (Significant Non-Cash Item) 0 0 0 141,802 [2]  
Interest Expense [2] 36,012 37,889 113,120 120,389  
Interest Income (3,939) (1,089) (8,620) (5,025)  
Income Tax Expense (Benefit) [2] 46,173 51,079 188,245 133,629  
Other Expense (Income) Items [3] 14,555 16,735 44,039 44,989  
Segment Profit: Net Income (Loss) 138,621 149,818 567,934 411,162  
Expenditures for Additions to Long-Lived Assets 288,863 222,870 744,540 595,956  
Segment Assets: 10,451,767   10,451,767   $ 8,719,104
Integrated Upstream and Gathering          
Segment Reporting [Line Items]          
Total Revenues 302,516 306,402 984,561 873,901  
Pipeline and Storage          
Segment Reporting [Line Items]          
Total Revenues 69,559 67,982 212,558 207,916  
Utility          
Segment Reporting [Line Items]          
Total Revenues 165,422 157,446 850,258 729,445  
Operating Segments          
Segment Reporting [Line Items]          
Total Revenues 574,557 569,504 2,160,018 1,925,390  
Operating Segments | Total Reportable Segments          
Segment Reporting [Line Items]          
Revenues From External Customers [1] 537,497 531,830 2,047,377 1,811,262  
Intersegment Revenues 37,060 37,674 112,641 114,128  
Total Revenues 574,557 569,504 2,160,018 1,925,390  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 17,487 18,602 55,365 56,776  
Lease Operating Expense [2] 15,847 12,566 50,034 35,710  
Gathering Operation and Maintenance Expense [2] 13,595 7,865 37,788 23,760  
All Other Operation and Maintenance Expense [2] 96,497 91,119 290,538 276,676  
Purchased Gas [2] 66,239 64,292 433,384 337,541  
Depreciation, Depletion and Amortization [2] 120,824 116,242 361,778 336,611  
Impairment of Assets (Significant Non-Cash Item) [2]       141,802  
Interest Expense [2] 36,008 39,962 113,575 127,267  
Interest Income (2,455) (1,742) (7,066) (7,847)  
Income Tax Expense (Benefit) [2] 48,699 52,547 194,117 136,812  
Other Expense (Income) Items [3] 15,517 17,530 45,864 45,018  
Segment Profit: Net Income (Loss) 146,299 150,521 584,641 415,264  
Expenditures for Additions to Long-Lived Assets 284,854 222,732 740,652 598,958  
Segment Assets: 9,431,892   9,431,892   8,648,682
Operating Segments | Integrated Upstream and Gathering          
Segment Reporting [Line Items]          
Revenues From External Customers [1] 302,516 306,402 984,561 873,901  
Intersegment Revenues 0 0 0 0  
Total Revenues 302,516 306,402 984,561 873,901  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 17,487 18,602 55,365 56,776  
Lease Operating Expense [2] 15,847 12,566 50,034 35,710  
Gathering Operation and Maintenance Expense [2] 13,595 7,865 37,788 23,760  
All Other Operation and Maintenance Expense [2] 3,366 3,816 9,847 10,994  
Purchased Gas [2] 0 0 0 0  
Depreciation, Depletion and Amortization [2] 83,078 79,696 247,888 228,970  
Impairment of Assets (Significant Non-Cash Item) [2]       141,802  
Interest Expense [2] 13,509 17,795 44,753 60,029  
Interest Income (414) (89) (986) (1,297)  
Income Tax Expense (Benefit) [2] 40,400 44,333 139,559 82,761  
Other Expense (Income) Items [3] 3,774 5,151 12,362 13,191  
Segment Profit: Net Income (Loss) 111,874 116,667 387,951 221,205  
Expenditures for Additions to Long-Lived Assets 146,327 150,007 453,903 412,519  
Segment Assets: 4,120,435   4,120,435   3,701,646
Operating Segments | Pipeline and Storage          
Segment Reporting [Line Items]          
Revenues From External Customers [1] 69,559 67,982 212,558 207,916  
Intersegment Revenues 36,982 37,597 112,347 113,849  
Total Revenues 106,541 105,579 324,905 321,765  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 0 0 0 0  
Lease Operating Expense [2] 0 0 0 0  
Gathering Operation and Maintenance Expense [2] 0 0 0 0  
All Other Operation and Maintenance Expense [2] 31,479 30,264 89,913 87,940  
Purchased Gas [2] 0 0 0 0  
Depreciation, Depletion and Amortization [2] 19,656 18,601 58,719 55,733  
Impairment of Assets (Significant Non-Cash Item) [2]       0  
Interest Expense [2] 11,735 11,209 35,314 34,637  
Interest Income (1,129) (1,116) (2,964) (4,919)  
Income Tax Expense (Benefit) [2] 9,417 10,415 30,341 32,553  
Other Expense (Income) Items [3] 6,644 7,349 22,017 22,802  
Segment Profit: Net Income (Loss) 28,739 28,857 91,565 93,019  
Expenditures for Additions to Long-Lived Assets 91,571 22,700 166,199 58,117  
Segment Assets: 2,690,056   2,690,056   2,412,747
Operating Segments | Utility          
Segment Reporting [Line Items]          
Revenues From External Customers [1] 165,422 157,446 850,258 729,445  
Intersegment Revenues 78 77 294 279  
Total Revenues 165,500 157,523 850,552 729,724  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 0 0 0 0  
Lease Operating Expense [2] 0 0 0 0  
Gathering Operation and Maintenance Expense [2] 0 0 0 0  
All Other Operation and Maintenance Expense [2] 61,652 57,039 190,778 177,742  
Purchased Gas [2] 66,239 64,292 433,384 337,541  
Depreciation, Depletion and Amortization [2] 18,090 17,945 55,171 51,908  
Impairment of Assets (Significant Non-Cash Item) [2]       0  
Interest Expense [2] 10,764 10,958 33,508 32,601  
Interest Income (912) (537) (3,116) (1,631)  
Income Tax Expense (Benefit) [2] (1,118) (2,201) 24,217 21,498  
Other Expense (Income) Items [3] 5,099 5,030 11,485 9,025  
Segment Profit: Net Income (Loss) 5,686 4,997 105,125 101,040  
Expenditures for Additions to Long-Lived Assets 46,956 50,025 120,550 128,322  
Segment Assets: 2,621,401   2,621,401   2,534,289
All Other          
Segment Reporting [Line Items]          
Total Revenues 0 0 0 0  
All Other | All Other          
Segment Reporting [Line Items]          
Revenues From External Customers [1],[4] 0 0 0 0  
Intersegment Revenues [4] 0 0 0 0  
Total Revenues [4] 0 0 0 0  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2],[4] 0 0 0 0  
Lease Operating Expense [2],[4] 0 0 0 0  
Gathering Operation and Maintenance Expense [2],[4] 0 0 0 0  
All Other Operation and Maintenance Expense [4] 0 [2] 0 0 [2] 0 [2]  
Purchased Gas [2],[4] 0 0 0 0  
Depreciation, Depletion and Amortization [2],[4] 0 0 0 0  
Impairment of Assets (Significant Non-Cash Item) [2],[4]       0  
Interest Expense [2],[4] 122 141 376 389  
Interest Income [4] 0 (11) (10) (11)  
Income Tax Expense (Benefit) [2],[4] (72) (63) 154 (204)  
Other Expense (Income) Items [3],[4] 172 142 (1,043) 500  
Segment Profit: Net Income (Loss) [4] (222) (209) 523 (674)  
Expenditures for Additions to Long-Lived Assets [4] 0 0 0 0  
Segment Assets: [4] 10,496   10,496   8,704
Corporate          
Segment Reporting [Line Items]          
Revenues From External Customers [1],[4] 0 0 0 0  
Corporate and Intersegment Eliminations          
Segment Reporting [Line Items]          
Intersegment Revenues [4] (37,060) (37,674) (112,641) (114,128)  
Total Revenues [4] (37,060) (37,674) (112,641) (114,128)  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2],[4] (63) (59) (188) (177)  
Lease Operating Expense [2],[4] (532) (1,303) (1,855) (4,513)  
Gathering Operation and Maintenance Expense [2],[4] (69) (65) (207) (194)  
All Other Operation and Maintenance Expense [2],[4] 12,377 4,279 25,437 10,562  
Purchased Gas [2],[4] (36,361) (36,306) (110,049) (108,880)  
Depreciation, Depletion and Amortization [2],[4] 234 166 634 444  
Impairment of Assets (Significant Non-Cash Item) [2],[4]       0  
Interest Expense [2],[4] (118) (2,214) (831) (7,267)  
Interest Income [4] (1,484) 664 (1,544) 2,833  
Income Tax Expense (Benefit) [2],[4] (2,454) (1,405) (6,026) (2,979)  
Other Expense (Income) Items [3],[4] (1,134) (937) (782) (529)  
Segment Profit: Net Income (Loss) [4] (7,456) (494) (17,230) (3,428)  
Expenditures for Additions to Long-Lived Assets [4] 4,009 $ 138 3,888 $ (3,002)  
Segment Assets: [4] $ 1,009,379   $ 1,009,379   $ 61,718
[1] All Revenue from External Customers originated in the United States.
[2] The Company considers this line to be a significant expense.
[3] Consists of Property, Franchise and Other Taxes, Non-Service Pension and Post-Retirement Benefits Costs (Credits), Other (Income) Deductions, and Purchased Gas Expense for the Pipeline and Storage Segment.
[4] Corporate and All Other categories primarily represent other non-segment business activities and eliminating entries.