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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Schedule of Assets Measured at Fair Value (Details) - USD ($) $ in Thousands | Dec. 31, 2024 | Sep. 30, 2024
--- | --- | ---
Short-term investments: |  |
Total short-term investments | $ 135,317 | $ 292,919
Recurring Fair Value Measurements |  |
Long-term Investments: |  |
Non-qualified supplemental savings plan | 16,275 | 15,633
Total | 70,572 | 70,223
Recurring Fair Value Measurements | Tamboran Resources Limited |  |
Long-term Investments: |  |
Equity securities, investment | 19,810 | 20,958
Recurring Fair Value Measurements | Galileo Technologies |  |
Long-term Investments: |  |
Debt securities, investment | 27,499 | 27,044
Recurring Fair Value Measurements | Geothermal Investments |  |
Long-term Investments: |  |
Debt securities, investment | 2,000 | 2,000
Recurring Fair Value Measurements | Other |  |
Long-term Investments: |  |
Debt securities, investment | 4,988 | 4,588
Fair Value, Nonrecurring |  |
Long-term Investments: |  |
Equity securities, investment | 4,600 | 4,300
Fair Value, Nonrecurring | Geothermal Investments |  |
Long-term Investments: |  |
Equity securities, investment | 26,200 | 25,800
Level 1 |  |
Short-term investments: |  |
Total short-term investments | 109,083 | 259,106
Level 1 | Recurring Fair Value Measurements |  |
Long-term Investments: |  |
Non-qualified supplemental savings plan | 16,275 | 15,633
Total | 40,823 | 40,929
Level 1 | Recurring Fair Value Measurements | Tamboran Resources Limited |  |
Long-term Investments: |  |
Equity securities, investment | 19,810 | 20,958
Level 1 | Recurring Fair Value Measurements | Galileo Technologies |  |
Long-term Investments: |  |
Debt securities, investment | 0 | 0
Level 1 | Recurring Fair Value Measurements | Geothermal Investments |  |
Long-term Investments: |  |
Debt securities, investment | 0 | 0
Level 1 | Recurring Fair Value Measurements | Other |  |
Long-term Investments: |  |
Debt securities, investment | 4,738 | 4,338
Level 2 |  |
Short-term investments: |  |
Total short-term investments | 26,234 | 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 | Tamboran Resources Limited |  |
Long-term Investments: |  |
Equity securities, investment | 0 | 0
Level 2 | Recurring Fair Value Measurements | Galileo Technologies |  |
Long-term Investments: |  |
Debt securities, investment | 0 | 0
Level 2 | Recurring Fair Value Measurements | Geothermal Investments |  |
Long-term Investments: |  |
Debt securities, investment | 0 | 0
Level 2 | Recurring Fair Value Measurements | Other |  |
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
Debt securities, investment | 27,500 | 27,000
Total | 29,749 | 29,294
Level 3 | Recurring Fair Value Measurements | Tamboran Resources Limited |  |
Long-term Investments: |  |
Equity securities, investment | 0 | 0
Level 3 | Recurring Fair Value Measurements | Galileo Technologies |  |
Long-term Investments: |  |
Debt securities, investment | 27,499 | 27,044
Level 3 | Recurring Fair Value Measurements | Geothermal Investments |  |
Long-term Investments: |  |
Debt securities, investment | 2,000 | 2,000
Level 3 | Recurring Fair Value Measurements | Other |  |
Long-term Investments: |  |
Debt securities, investment |  | 250
Money market mutual funds |  |
Short-term investments: |  |
Total short-term investments | 72,305 |
Money market mutual funds | Level 1 |  |
Short-term investments: |  |
Total short-term investments | 72,305 |
Money market mutual funds | Level 2 |  |
Short-term investments: |  |
Total short-term investments | 0 |
Money market mutual funds | Level 3 |  |
Short-term investments: |  |
Total short-term investments | 0 |
Corporate and municipal debt securities |  |
Short-term investments: |  |
Total short-term investments | 26,234 | 33,813
Corporate and municipal debt securities | Level 1 |  |
Short-term investments: |  |
Total short-term investments | 0 | 0
Corporate and municipal debt securities | Level 2 |  |
Short-term investments: |  |
Total short-term investments | 26,234 | 33,813
Corporate and municipal 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 | 36,778 | 53,490
U.S. government and federal agency securities | Level 1 |  |
Short-term investments: |  |
Total short-term investments | 36,778 | 53,490
U.S. government and federal agency securities | Level 2 |  |
Short-term investments: |  |
Total short-term investments | 0 | 0
U.S. government and federal agency securities | Level 3 |  |
Short-term investments: |  |
Total short-term investments | $ 0 | 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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