SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) - USD ($)	1 Months Ended		3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Finite-Lived Intangible Assets [Line Items]
Loans receivable in other current assets	$ 14,400,000		$ 14,400,000		$ 13,700,000
Loans receivable in other noncurrent assets	34,700,000		34,700,000		$ 35,300,000
Proceeds from sale leaseback transaction - solar	$ 12,100,000		12,124,000	$ 0
Natural Gas Distribution
Finite-Lived Intangible Assets [Line Items]
Proceeds from sale-leaseback transaction		$ 4,000,000.0	$ 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term			2 years
Minimum | Clean Energy Ventures
Finite-Lived Intangible Assets [Line Items]
Sale leaseback transaction lease term			5 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term			10 years
Maximum | Clean Energy Ventures
Finite-Lived Intangible Assets [Line Items]
Sale leaseback transaction lease term			15 years