SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Mar. 31, 2022	Mar. 31, 2021	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Operating revenues	$ 912,316	$ 802,187	$ 1,588,158	$ 1,256,492
Loans receivable in other noncurrent assets	33,700		33,700		$ 32,300
Proceeds from sale leaseback transactions			17,300	0
Proceeds from sale leaseback transactions - solar			3,300	12,124
Financial Asset, Not Past Due
Finite-Lived Intangible Assets [Line Items]
Loans receivable in other current assets	14,500		14,500		$ 14,200
Energy Services
Finite-Lived Intangible Assets [Line Items]
Operating revenues	10,300		32,400
Deferred revenue	$ 54,400		54,400
Natural Gas Distribution
Finite-Lived Intangible Assets [Line Items]
Proceeds from sale leaseback transactions			$ 17,300	$ 0
Minimum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term			2 years
Maximum
Finite-Lived Intangible Assets [Line Items]
Loans receivable, term			10 years