SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Jul. 31, 2021 Megawatt	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Sep. 30, 2022 USD ($)
Finite-Lived Intangible Assets [Line Items]
Number of megawatts | Megawatt	5
Operating revenues		$ 264,075	$ 552,335	$ 1,631,669	$ 2,140,493
Loans receivable in other noncurrent assets		36,900		36,900		$ 34,700
Financial Asset, Not Past Due
Finite-Lived Intangible Assets [Line Items]
Loans receivable in other current assets		15,000		$ 15,000		14,500
Minimum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term				2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term				10 years
Energy Services
Finite-Lived Intangible Assets [Line Items]
Operating revenues		9,500	$ 10,300	$ 39,000	$ 42,700
Deferred revenue		$ 68,200		$ 68,200		$ 33,800