REPORTING SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS (LOSS) RECONCILIATION (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2021	Jun. 30, 2020
Segment Reporting [Abstract]
Net financial earnings (loss)	$ (14,148)			$ 2,682			$ 201,113	$ 121,904
Less:
Unrealized loss (gain) on derivative instruments and related transactions	21,862			23,712			13,627	(21,827)
Tax effect	(5,198)			(5,639)			(3,240)	5,189
Effects of economic hedging related to natural gas inventory	2,486			4,739			(12,255)	10,474
Tax effect	(591)			(1,126)			2,912	(2,489)
Other than temporary impairment	92,000			0			92,000	0
Tax effect	(11,934)			0			(11,934)	0
NFE tax adjustment	(942)			294			980	257
NET (LOSS) INCOME	$ (111,831)	$ 149,809	$ 81,045	$ (19,298)	$ 73,846	$ 75,752	$ 119,023	$ 130,300