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FAIR VALUE MEASUREMENT OF FINANCIAL INSTRUMENTS - Narrative (Details) - USD ($) $ in Thousands, shares in Millions | 1 Months Ended | 3 Months Ended | 12 Months Ended |
--- | --- | --- | --- | ---
Sep. 30, 2024 | Oct. 31, 2022 | Apr. 30, 2022 | Sep. 30, 2021 | Dec. 31, 2024 | Sep. 30, 2025 | Sep. 30, 2024 | Sep. 30, 2023 | Sep. 30, 2022
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Investments lockup period expiration (in years) | 3 years |  |  |  | 180 days |  |  |  |
Gain (loss) resulting from the change in the fair value of investments |  |  |  |  |  |  | $ 30,900 | $ 27,400 |
Convertible notes |  |  |  |  |  | $ 9,400 |  |  |
Convertible notes (in shares) |  |  |  |  |  | 0.5 |  |  |
Investment shares |  |  |  |  |  | 1.0 |  |  |
Unrealized loss on investments |  |  |  |  |  | $ 5,000 | 1,600 | (4,200) |
Annual expense incurred for defined contribution plan |  |  |  |  |  | 23,600 | 26,900 | $ 25,800 |
KCA Deutag |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Annual expense incurred for defined contribution plan |  |  |  |  |  | 10,000 |  |  |
Debt Securities | Level 3 |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Included in earnings |  |  |  |  |  | (29,287) | (10,167) |  |
Debt Securities | Level 3 | Notes Receivable |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Included in earnings |  |  |  |  |  | 29,600 |  |  |
Convertible Debt | Investment in Galileo, net |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Interest rate (as a percent) |  |  | 5.00% |  |  |  |  |  |
ADNOC Drilling |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire investments |  |  |  | $ 100,000 |  |  |  |  |
Investment balance (in shares) |  |  |  |  |  |  |  |  | 159.7
Investments lockup period (in years) |  |  |  | 3 years |  |  |  |  |
Increase (decrease) in equity securities, FV-NI |  |  |  |  |  | 193,300 |  |  |
Gain (loss) resulting from the change in the fair value of investments |  |  |  |  |  | (12,400) |  |  |
Fair value of the investment |  |  |  |  |  | 8,400 |  |  |
Equity securities, FV-NI, transaction fee associated with sale of securities |  |  |  |  |  | $ 4,000 |  |  |
ADNOC Drilling | ADNOC Drilling |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage (as a percent) |  |  |  |  |  |  |  |  | 1.00%
Investment in Tamboran |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire investments |  | $ 14,100 |  |  |  |  |  |  |
Investment shares acquired (in shares) |  | 106.0 |  |  |  |  |  |  |
Depository beneficial interests |  | 0.50% |  |  |  |  |  |  |
Investment in Tamboran | Tamboran Corp |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Ownership percentage (as a percent) |  |  |  |  |  | 610.00% |  |  |
Investment in Galileo, net |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Payments to acquire investments |  |  | $ 33,000 |  |  |  |  |  |
Nonrecurring Fair Value Measurements |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Debt security investments | $ 300 |  |  |  |  | $ 200 | 300 |  |
Investment in Tamboran | 4,300 |  |  |  |  | 6,700 | 4,300 |  |
Nonrecurring Fair Value Measurements | Geothermal debt securities, net |  |  |  |  |  |  |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |  |  |  |  |  |  |
Investment in Tamboran | 25,800 |  |  |  |  | $ 14,100 | 25,800 |  |
Geothermal equity securities | 100 |  |  |  |  |  | 100 |  |
Equity securities measured at cost | $ 25,700 |  |  |  |  |  | $ 25,700 |  |

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