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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Schedule of Assets Measured at Fair Value (Details) - USD ($) $ in Thousands | Jun. 30, 2026 | Sep. 30, 2025
--- | --- | ---
Short-term investments: |  |
Total | $ 26,960 | $ 21,302
Long-term Investments: |  |
Total | 54,109 | 47,337
Level 1 |  |
Short-term investments: |  |
Total | 5,040 | 0
Long-term Investments: |  |
Total | 51,859 | 45,087
Level 2 |  |
Short-term investments: |  |
Total | 21,920 | 21,302
Long-term Investments: |  |
Total | 0 | 0
Level 3 |  |
Short-term investments: |  |
Total | 0 | 0
Long-term Investments: |  |
Total | 2,250 | 2,250
Money market mutual funds |  |
Short-term investments: |  |
Total | 5,040 |
Money market mutual funds | Level 1 |  |
Short-term investments: |  |
Total | 5,040 |
Money market mutual funds | Level 2 |  |
Short-term investments: |  |
Total | 0 |
Money market mutual funds | Level 3 |  |
Short-term investments: |  |
Total | 0 |
Corporate debt securities |  |
Short-term investments: |  |
Total | 21,920 | 21,302
Corporate debt securities | Level 1 |  |
Short-term investments: |  |
Total | 0 | 0
Corporate debt securities | Level 2 |  |
Short-term investments: |  |
Total | 21,920 | 21,302
Corporate debt securities | Level 3 |  |
Short-term investments: |  |
Total | 0 | 0
Non-qualified supplemental savings plan |  |
Long-term Investments: |  |
Equity securities: | 19,196 | 17,662
Non-qualified supplemental savings plan | Level 1 |  |
Long-term Investments: |  |
Equity securities: | 19,196 | 17,662
Non-qualified supplemental savings plan | Level 2 |  |
Long-term Investments: |  |
Equity securities: | 0 | 0
Non-qualified supplemental savings plan | Level 3 |  |
Long-term Investments: |  |
Equity securities: | 0 | 0
Tamboran Resources Limited |  |
Long-term Investments: |  |
Equity securities: | 32,663 | 25,976
Tamboran Resources Limited | Level 1 |  |
Long-term Investments: |  |
Equity securities: | 32,663 | 25,976
Tamboran Resources Limited | Level 2 |  |
Long-term Investments: |  |
Equity securities: | 0 | 0
Tamboran Resources Limited | Level 3 |  |
Long-term Investments: |  |
Equity securities: | 0 | 0
Other equity securities |  |
Long-term Investments: |  |
Equity securities: |  | 1,449
Other equity securities | Level 1 |  |
Long-term Investments: |  |
Equity securities: |  | 1,449
Other equity securities | Level 2 |  |
Long-term Investments: |  |
Equity securities: |  | 0
Other equity securities | Level 3 |  |
Long-term Investments: |  |
Equity securities: |  | 0
Geothermal Investments |  |
Long-term Investments: |  |
Debt securities: | 2,000 | 2,000
Geothermal Investments | Level 1 |  |
Long-term Investments: |  |
Debt securities: | 0 | 0
Geothermal Investments | Level 2 |  |
Long-term Investments: |  |
Debt securities: | 0 | 0
Geothermal Investments | Level 3 |  |
Long-term Investments: |  |
Debt securities: | 2,000 | 2,000
Other debt securities |  |
Long-term Investments: |  |
Debt securities: | 250 | 250
Other debt securities | Level 1 |  |
Long-term Investments: |  |
Debt securities: | 0 | 0
Other debt securities | Level 2 |  |
Long-term Investments: |  |
Debt securities: | 0 | 0
Other debt securities | Level 3 |  |
Long-term Investments: |  |
Debt securities: | $ 250 | $ 250

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