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