v3.26.1
Business Segment Information - (Schedule of Information By Segment) (Details) - USD ($)
$ in Thousands
 3 Months Ended 6 Months Ended
Mar. 31, 2026
Mar. 31, 2025
Mar. 31, 2026
Mar. 31, 2025
Sep. 30, 2025
Segment Reporting Information [Line Items]          
Revenues From External Customers [1] $ 858,373 $ 729,950 $ 1,509,881 $ 1,279,432  
Intersegment Revenues 0 0 0 0  
Total Revenues 858,373 729,950 1,509,881 1,279,432  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 18,409 18,788 37,753 38,055  
Lease Operating Expense [2] 16,828 10,871 32,864 19,935  
Gathering Operation and Maintenance Expense [2] 13,736 9,095 24,055 15,765  
All Other Operation and Maintenance Expense [2] 109,811 102,115 207,101 191,840  
Purchased Gas [2] 207,851 135,338 293,457 200,675  
Depreciation, Depletion and Amortization [2] 119,329 111,277 241,354 220,647  
Impairment of Assets (Significant Non-Cash Item) 0 0 0 141,802 [2]  
Interest Expense [2] 33,734 44,757 77,110 82,500  
Interest Income (1,903) (2,252) (4,681) (3,935)  
Income Tax Expense (Benefit) [2] 82,735 71,369 142,072 82,551  
Other Expense (Income) Items [3] 10,175 12,234 29,483 28,253  
Segment Profit: Net Income (Loss) 247,668 216,358 429,313 261,344  
Expenditures for Additions to Long-Lived Assets 232,956 181,030 455,677 373,085  
Segment Assets: 9,127,604   9,127,604   $ 8,719,104
Operating Segments          
Segment Reporting Information [Line Items]          
Total Revenues 896,200 768,457 1,585,461 1,355,886  
All Other          
Segment Reporting Information [Line Items]          
Total Revenues 0 0 0 0  
Corporate          
Segment Reporting Information [Line Items]          
Revenues From External Customers [1],[4] 0 0 0 0  
Corporate and Intersegment Eliminations          
Segment Reporting Information [Line Items]          
Intersegment Revenues [4] (37,827) (38,507) (75,580) (76,454)  
Total Revenues [4] (37,827) (38,507) (75,580) (76,454)  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2],[4] (63) (59) (125) (118)  
Lease Operating Expense [2],[4] (534) (1,623) (1,323) (3,210)  
Gathering Operation and Maintenance Expense [2],[4] (69) (65) (138) (129)  
All Other Operation and Maintenance Expense [2],[4] 7,408 3,719 13,059 6,281  
Purchased Gas [2],[4] (37,009) (36,439) (73,688) (72,574)  
Depreciation, Depletion and Amortization [2],[4] 219 139 400 279  
Impairment of Assets (Significant Non-Cash Item) [2],[4]       0  
Interest Expense [2],[4] (4,412) (825) (713) (5,054)  
Interest Income [4] 512 519 (60) 2,170  
Income Tax Expense (Benefit) [2],[4] (1,133) (1,066) (3,572) (1,573)  
Other Expense (Income) Items [3],[4] (561) (15) 354 408  
Segment Profit: Net Income (Loss) [4] (2,185) (2,792) (9,774) (2,934)  
Expenditures for Additions to Long-Lived Assets [4] (297) 174 (121) 378  
Segment Assets: [4] (114,806)   (114,806)   61,718
Total Reportable Segments | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues From External Customers [1] 858,373 729,950 1,509,881 1,279,432  
Intersegment Revenues 37,827 38,507 75,580 76,454  
Total Revenues 896,200 768,457 1,585,461 1,355,886  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 18,472 18,847 37,878 38,173  
Lease Operating Expense [2] 17,362 12,494 34,187 23,145  
Gathering Operation and Maintenance Expense [2] 13,805 9,160 24,193 15,894  
All Other Operation and Maintenance Expense [2] 102,403 98,396 194,042 185,559  
Purchased Gas [2] 244,860 171,777 367,145 273,249  
Depreciation, Depletion and Amortization [2] 119,110 111,138 240,954 220,368  
Impairment of Assets (Significant Non-Cash Item) [2]       141,802  
Interest Expense [2] 38,028 45,451 77,569 87,306  
Interest Income (2,415) (2,771) (4,611) (6,105)  
Income Tax Expense (Benefit) [2] 83,606 72,517 145,419 84,265  
Other Expense (Income) Items [3] 11,984 12,027 30,344 27,487  
Segment Profit: Net Income (Loss) 248,985 219,421 438,341 264,743  
Expenditures for Additions to Long-Lived Assets 233,253 180,856 455,798 372,707  
Segment Assets: 9,232,522   9,232,522   8,648,682
Integrated Upstream and Gathering          
Segment Reporting Information [Line Items]          
Total Revenues 358,823 315,191 682,045 567,499  
Integrated Upstream and Gathering | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues From External Customers [1] 358,823 315,191 682,045 567,499  
Intersegment Revenues 0 0 0 0  
Total Revenues 358,823 315,191 682,045 567,499  
Operation and Maintenance Expense          
Upstream General and Administrative Expense [2] 18,472 18,847 37,878 38,173  
Lease Operating Expense [2] 17,362 12,494 34,187 23,145  
Gathering Operation and Maintenance Expense [2] 13,805 9,160 24,193 15,894  
All Other Operation and Maintenance Expense [2] 3,102 3,310 6,481 7,178  
Purchased Gas [2] 0 0 0 0  
Depreciation, Depletion and Amortization [2] 80,548 75,456 164,810 149,274  
Impairment of Assets (Significant Non-Cash Item) [2]       141,802  
Interest Expense [2] 15,111 22,824 31,245 42,235  
Interest Income (380) (529) (573) (1,208)  
Income Tax Expense (Benefit) [2] 55,049 44,879 99,159 38,428  
Other Expense (Income) Items [3] 3,724 4,580 8,588 8,040  
Segment Profit: Net Income (Loss) 152,030 124,170 276,077 104,538  
Expenditures for Additions to Long-Lived Assets 165,727 123,363 307,576 258,992  
Segment Assets: 4,011,274   4,011,274   3,701,646
Pipeline and Storage          
Segment Reporting Information [Line Items]          
Total Revenues 73,762 71,185 142,999 139,935  
Pipeline and Storage | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues From External Customers [1] 73,762 71,185 142,999 139,935  
Intersegment Revenues 37,701 38,388 75,365 76,251  
Total Revenues 111,463 109,573 218,364 216,186  
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] 31,172 30,642 58,435 57,677  
Purchased Gas [2] 0 0 0 0  
Depreciation, Depletion and Amortization [2] 19,961 18,547 39,063 37,132  
Impairment of Assets (Significant Non-Cash Item) [2]       0  
Interest Expense [2] 11,779 11,700 23,580 23,428  
Interest Income (870) (1,797) (1,835) (3,803)  
Income Tax Expense (Benefit) [2] 10,558 10,961 20,925 22,138  
Other Expense (Income) Items [3] 7,257 7,813 15,371 15,452  
Segment Profit: Net Income (Loss) 31,606 31,707 62,825 64,162  
Expenditures for Additions to Long-Lived Assets 37,026 15,626 74,628 35,417  
Segment Assets: 2,528,382   2,528,382   2,412,747
Utility          
Segment Reporting Information [Line Items]          
Total Revenues 425,788 343,574 684,837 571,998  
Utility | Operating Segments          
Segment Reporting Information [Line Items]          
Revenues From External Customers [1] 425,788 343,574 684,837 571,998  
Intersegment Revenues 126 119 215 203  
Total Revenues 425,914 343,693 685,052 572,201  
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] 68,129 64,444 129,126 120,704  
Purchased Gas [2] 244,860 171,777 367,145 273,249  
Depreciation, Depletion and Amortization [2] 18,601 17,135 37,081 33,962  
Impairment of Assets (Significant Non-Cash Item) [2]       0  
Interest Expense [2] 11,138 10,927 22,744 21,643  
Interest Income (1,165) (445) (2,203) (1,094)  
Income Tax Expense (Benefit) [2] 17,999 16,677 25,335 23,699  
Other Expense (Income) Items [3] 1,003 (366) 6,385 3,995  
Segment Profit: Net Income (Loss) 65,349 63,544 99,439 96,043  
Expenditures for Additions to Long-Lived Assets 30,500 41,867 73,594 78,298  
Segment Assets: 2,692,866   2,692,866   2,534,289
All Other | All Other          
Segment Reporting Information [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] 118 131 254 248  
Interest Income [4] 0 0 (10) 0  
Income Tax Expense (Benefit) [2],[4] 262 (82) 225 (141)  
Other Expense (Income) Items [3],[4] (1,248) 222 (1,215) 358  
Segment Profit: Net Income (Loss) [4] 868 (271) 746 (465)  
Expenditures for Additions to Long-Lived Assets [4] 0 $ 0 0 $ 0  
Segment Assets: [4] $ 9,888   $ 9,888   $ 8,704
[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.