SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - ADDITIONAL INFORMATION (Details) - USD ($) $ in Thousands	3 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Sep. 30, 2021
Finite-Lived Intangible Assets [Line Items]
Operating revenues	$ 675,842	$ 454,305
Loans receivable in other noncurrent assets	32,600		$ 32,300
Proceeds from sale leaseback transaction	17,300	0
Proceeds from sale leaseback transaction - solar	3,300	12,124
Financial Asset, Not Past Due
Finite-Lived Intangible Assets [Line Items]
Loans receivable in other current assets	14,100		$ 14,200
Energy Services
Finite-Lived Intangible Assets [Line Items]
Operating revenues	22,100
Deferred revenue	64,700
Natural Gas Distribution
Finite-Lived Intangible Assets [Line Items]
Proceeds from sale leaseback transaction	$ 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