SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Jul. 31, 2021 Megawatt	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2024 USD ($)	Mar. 31, 2023 USD ($)	Sep. 30, 2023 USD ($)
Finite-Lived Intangible Assets [Line Items]
Number of megawatts | Megawatt	5
Operating revenues		$ 657,913	$ 644,027	$ 1,125,123	$ 1,367,594
Loans receivable in other noncurrent assets		43,600		43,600		$ 39,000
Financial Asset, Not Past Due
Finite-Lived Intangible Assets [Line Items]
Loans receivable in other current assets		15,800		$ 15,800		15,100
Minimum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term				2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term				10 years
ES
Finite-Lived Intangible Assets [Line Items]
Operating revenues		9,500	$ 9,500	$ 19,000	$ 29,500
Deferred revenue		$ 107,200		$ 107,200		$ 58,700