Summary of Significant Accounting Policies (Schedule of Other Accruals and Current Liabilities) (Details) - USD ($) $ in Thousands |
Jun. 30, 2026 |
Sep. 30, 2025 |
|---|---|---|
| Summary Of Significant Accounting Policies [Line Items] | ||
| Accrued Capital Expenditures | $ 63,908 | $ 45,932 |
| Regulatory Liabilities | 17,737 | 20,624 |
| Reserve for Gas Replacement | 19,793 | 0 |
| Liability for Royalty and Working Interests | 27,038 | 28,076 |
| Pennsylvania Impact Fee | 7,479 | 14,923 |
| Non-Qualified Benefit Plan Liability | 11,567 | 11,567 |
| Other | 58,617 | 53,567 |
| Other Accruals and Current Liabilities | 241,398 | 174,689 |
| Federal Income Taxes Payable | ||
| Summary Of Significant Accounting Policies [Line Items] | ||
| Federal Income Taxes Payable | 25,631 | 0 |
| State Income Taxes Payable | ||
| Summary Of Significant Accounting Policies [Line Items] | ||
| Federal Income Taxes Payable | $ 9,628 | $ 0 |