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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, 2024 | Mar. 31, 2023 | Mar. 31, 2024 | Mar. 31, 2023 | Sep. 30, 2023 | Sep. 30, 2024
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Gas Stored Underground | $ 8,565 |  | $ 8,565 |  | $ 32,509 |
Capitalized Costs Oil and Gas Producing Activities Net | $ 2,600,000 |  | 2,600,000 |  | 2,400,000 |
Capitalized costs of unproved properties excluded from amortization |  |  | $ 174,000 |  | $ 161,100 |
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 | $ 3,100 |  | $ 3,100 |  |  |
Increase estimated future net cash flows | $ 347,100 |  |  |  |  |
Antidilutive securities (in shares) | 232 | 9,909 | 0 | 4,094 |  |
Number of shares available for future grant (in shares) | 3,842,625 |  | 3,842,625 |  |  |
Reserve For Gas Replacement |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Gas Stored Underground | $ 20,100 |  | $ 20,100 |  |  |
Restricted Stock Units |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Share based compensation other than options grants in period (in shares) |  |  | 220,778 |  |  |
Granted in fiscal year, weighted average grant date fair value (in USD per share) |  |  | $ 42.44 |  |  |
Performance Shares |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Share based compensation other than options grants in period (in shares) |  |  | 361,729 |  |  |
Granted in fiscal year, weighted average grant date fair value (in USD per share) |  |  | $ 44.23 |  |  |
Greenhouse gas emissions reductions, performance cycle |  |  | 3 years |  |  |
Performance Shares | Minimum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Return on capital, performance cycle (in years) |  |  | 3 years |  |  |
Relative shareholder return, performance cycle |  |  | 3 years |  |  |
Performance Shares | Maximum |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Return on capital, performance cycle (in years) |  |  | 5 years |  |  |
Relative shareholder return, performance cycle |  |  | 5 years |  |  |
Subsequent Event | Reserve For Gas Replacement |  |  |  |  |  |
Summary Of Significant Accounting Policies [Line Items] |  |  |  |  |  |
Gas Stored Underground |  |  |  |  |  | $ 0

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