LEASES - ADDITIONAL INFORMATION (Details) - USD ($)	3 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Sep. 30, 2020
Lessee, Lease, Description [Line Items]
ROU asset obtained in exchange for operating lease liability	$ 9,300,000	$ 21,600,000
ROU asset obtained in exchange for finance lease liability	$ 0	$ 4,000,000.0
Weighted average remaining lease term, operating lease	27 years 10 months 24 days		25 years 6 months
Operating lease, discount rate	3.30%		3.20%
Weighted average remaining lease term, finance lease	11 years 8 months 12 days		11 years 6 months
Finance lease, discount rate	2.50%		2.50%
Solar Property | Minimum
Lessee, Lease, Description [Line Items]
Term of contract	15 years
Renewal term	5 years
Solar Property | Maximum
Lessee, Lease, Description [Line Items]
Term of contract	35 years
Renewal term	10 years
Office Building | Minimum
Lessee, Lease, Description [Line Items]
Term of contract	1 year
Office Building | Maximum
Lessee, Lease, Description [Line Items]
Term of contract	25 years
Meter License
Lessee, Lease, Description [Line Items]
Term of contract	7 years
Equipment
Lessee, Lease, Description [Line Items]
Term of contract	5 years
Storage and Capacity
Lessee, Lease, Description [Line Items]
Term of contract	50 years