REPORTING SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2019
Segment Reporting [Abstract]
Net financial earnings	$ 207,712	$ 165,333	$ 129,390
Less:
Unrealized loss (gain) on derivative instruments and related transactions	54,203	(9,644)	2,881
Unrealized loss (gain) on derivative instruments and related transactions, tax effect	(12,887)	2,296	(711)
Effects of economic hedging related to natural gas inventory	(42,405)	12,690	4,309
Effects of economic hedging related to natural gas inventory, tax effect	10,078	(3,016)	(1,024)
Impairment of equity method investment	92,000	0	0
Impairment of equity method investment, tax effect	(11,167)	0	0
NET INCOME	$ 117,890	$ 163,007	$ 123,935