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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