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Summary Of Significant Accounting Policies (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Mar. 31, 2025 | Dec. 31, 2024 | Mar. 31, 2024 | Mar. 31, 2025 | Mar. 31, 2024 | Sep. 30, 2024 | Sep. 30, 2025
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Gas Stored Underground | $ 6,413 |  |  | $ 6,413 |  | $ 35,055 |
Capitalized Costs Exploration and Production Activities Net | $ 2,300,000 |  |  | 2,300,000 |  | 2,300,000 |
Capitalized costs of unproved properties excluded from amortization |  |  |  | $ 121,400 |  | $ 201,000 |
Full cost ceiling test discount factor (as a percent) | 10.00% |  |  | 10.00% |  |  |
Amount full cost ceiling exceeds book value of oil and gas properties | $ 395,500 |  |  | $ 395,500 |  |  |
Impairment of exploration and production properties |  | $ 108,300 |  |  |  |  |
Increase estimated future net cash flows | $ 462,400 |  |  |  |  |  |
Antidilutive securities (in shares) | 30 |  | 232 | 0 | 0 |  |
Impairment of Exploration and Production Properties |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Deferred income tax benefit |  | $ 29,200 |  |  |  |  |
Reserve For Gas Replacement |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Gas Stored Underground | $ 27,600 |  |  | $ 27,600 |  |  |
Reserve For Gas Replacement | Forecast |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Gas Stored Underground |  |  |  |  |  |  | $ 0
Restricted Stock Units |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Share based compensation other than options grants in period (in shares) |  |  |  | 132,352 |  |  |
Granted in fiscal year, weighted average grant date fair value (in USD per share) |  |  |  | $ 58.64 |  |  |
Performance Shares |  |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |  |
Share based compensation other than options grants in period (in shares) |  |  |  | 239,042 |  |  |
Granted in fiscal year, weighted average grant date fair value (in USD per share) |  |  |  | $ 55.43 |  |  |
Return on capital, performance cycle (in years) |  |  |  | 3 years |  |  |
Greenhouse gas emissions reductions, performance cycle |  |  |  | 3 years |  |  |
Relative shareholder return, performance cycle |  |  |  | 3 years |  |  |

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