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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Schedule of Assets Measured at Fair Value (Details) - USD ($) $ in Thousands | Sep. 30, 2025 | Sep. 30, 2024
--- | --- | ---
Short-term investments: |  |
Total short-term investments | $ 21,302 | $ 292,919
Recurring Fair Value Measurements |  |
Long-term investments: |  |
Non-qualified supplemental savings plan | 17,662 | 15,633
Total | 47,337 | 70,223
Recurring Fair Value Measurements | Investment in Tamboran |  |
Long-term investments: |  |
Investment in Tamboran | 25,976 | 20,958
Recurring Fair Value Measurements | Other Equity Securities |  |
Long-term investments: |  |
Investment in Tamboran | 1,449 |
Recurring Fair Value Measurements | Investment in Galileo, net |  |
Long-term investments: |  |
Debt securities, investment | 0 | 27,044
Recurring Fair Value Measurements | Geothermal debt securities, net |  |
Long-term investments: |  |
Debt securities, investment | 2,000 | 2,000
Recurring Fair Value Measurements | Other debt securities |  |
Long-term investments: |  |
Debt securities, investment | 250 | 4,588
Level 1 |  |
Short-term investments: |  |
Total short-term investments | 0 | 259,106
Level 1 | Recurring Fair Value Measurements |  |
Long-term investments: |  |
Non-qualified supplemental savings plan | 17,662 | 15,633
Total | 45,087 | 40,929
Level 1 | Recurring Fair Value Measurements | Investment in Tamboran |  |
Long-term investments: |  |
Investment in Tamboran | 25,976 | 20,958
Level 1 | Recurring Fair Value Measurements | Other Equity Securities |  |
Long-term investments: |  |
Investment in Tamboran | 1,449 |
Level 1 | Recurring Fair Value Measurements | Investment in Galileo, net |  |
Long-term investments: |  |
Debt securities, investment | 0 | 0
Level 1 | Recurring Fair Value Measurements | Geothermal debt securities, net |  |
Long-term investments: |  |
Debt securities, investment | 0 | 0
Level 1 | Recurring Fair Value Measurements | Other debt securities |  |
Long-term investments: |  |
Debt securities, investment | 0 | 4,338
Level 2 |  |
Short-term investments: |  |
Total short-term investments | 21,302 | 33,813
Level 2 | Recurring Fair Value Measurements |  |
Long-term investments: |  |
Non-qualified supplemental savings plan | 0 | 0
Total | 0 | 0
Level 2 | Recurring Fair Value Measurements | Investment in Tamboran |  |
Long-term investments: |  |
Investment in Tamboran | 0 | 0
Level 2 | Recurring Fair Value Measurements | Other Equity Securities |  |
Long-term investments: |  |
Investment in Tamboran | 0 |
Level 2 | Recurring Fair Value Measurements | Investment in Galileo, net |  |
Long-term investments: |  |
Debt securities, investment | 0 | 0
Level 2 | Recurring Fair Value Measurements | Geothermal debt securities, net |  |
Long-term investments: |  |
Debt securities, investment | 0 | 0
Level 2 | Recurring Fair Value Measurements | Other debt securities |  |
Long-term investments: |  |
Debt securities, investment | 0 | 0
Level 3 |  |
Short-term investments: |  |
Total short-term investments | 0 | 0
Level 3 | Recurring Fair Value Measurements |  |
Long-term investments: |  |
Non-qualified supplemental savings plan | 0 | 0
Total | 2,250 | 29,294
Level 3 | Recurring Fair Value Measurements | Investment in Tamboran |  |
Long-term investments: |  |
Investment in Tamboran | 0 | 0
Level 3 | Recurring Fair Value Measurements | Other Equity Securities |  |
Long-term investments: |  |
Investment in Tamboran | 0 |
Level 3 | Recurring Fair Value Measurements | Investment in Galileo, net |  |
Long-term investments: |  |
Debt securities, investment | 0 |
Level 3 | Recurring Fair Value Measurements | Geothermal debt securities, net |  |
Long-term investments: |  |
Debt securities, investment | 2,000 | 2,000
Level 3 | Recurring Fair Value Measurements | Other debt securities |  |
Long-term investments: |  |
Debt securities, investment | 250 | 250
Corporate debt securities |  |
Short-term investments: |  |
Total short-term investments | 21,302 | 33,813
Corporate debt securities | Level 1 |  |
Short-term investments: |  |
Total short-term investments | 0 | 0
Corporate debt securities | Level 2 |  |
Short-term investments: |  |
Total short-term investments | 21,302 | 33,813
Corporate debt securities | Level 3 |  |
Short-term investments: |  |
Total short-term investments | 0 | 0
U.S. government and federal agency securities |  |
Short-term investments: |  |
Total short-term investments |  | 53,490
U.S. government and federal agency securities | Level 1 |  |
Short-term investments: |  |
Total short-term investments |  | 53,490
U.S. government and federal agency securities | Level 2 |  |
Short-term investments: |  |
Total short-term investments |  | 0
U.S. government and federal agency securities | Level 3 |  |
Short-term investments: |  |
Total short-term investments |  | $ 0
Investment in ADNOC Drilling |  |
Short-term investments: |  |
Total short-term investments | 205,616 |
Investment in ADNOC Drilling | Level 1 |  |
Short-term investments: |  |
Total short-term investments | 205,616 |
Investment in ADNOC Drilling | Level 2 |  |
Short-term investments: |  |
Total short-term investments | 0 |
Investment in ADNOC Drilling | Level 3 |  |
Short-term investments: |  |
Total short-term investments | $ 0 |

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