Summary of Significant Accounting Policies (Schedule of Other Accruals and Current Liabilities) (Details) - USD ($) $ in Thousands |
Mar. 31, 2026 |
Sep. 30, 2025 |
|---|---|---|
| Summary Of Significant Accounting Policies [Line Items] | ||
| Accrued Capital Expenditures | $ 57,675 | $ 45,932 |
| Regulatory Liabilities | 20,235 | 20,624 |
| Reserve for Gas Replacement | 47,387 | 0 |
| Liability for Royalty and Working Interests | 44,108 | 28,076 |
| Pennsylvania Impact Fee | 3,680 | 14,923 |
| Non-Qualified Benefit Plan Liability | 11,567 | 11,567 |
| Other | 46,082 | 53,567 |
| Other Accruals and Current Liabilities | 242,760 | 174,689 |
| Federal Income Taxes Payable | ||
| Summary Of Significant Accounting Policies [Line Items] | ||
| Federal Income Taxes Payable | 7,029 | 0 |
| State Income Taxes Payable | ||
| Summary Of Significant Accounting Policies [Line Items] | ||
| Federal Income Taxes Payable | $ 4,997 | $ 0 |