REPORTING SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS (LOSS) RECONCILIATION (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Jun. 30, 2020	Jun. 30, 2019
Segment Reporting [Abstract]
Net financial earnings (loss)	$ (5,817)			$ (17,506)			$ 141,524	$ 149,004
Less:
Unrealized loss (gain) on derivative instruments and related transactions	23,712			(24,646)			(21,827)	(25,353)
Tax effect	(5,639)			5,885			5,189	6,034
Effects of economic hedging related to natural gas inventory	4,739			11,317			10,474	12,073
Tax effect	(1,126)			(2,689)			(2,489)	(2,869)
NFE tax adjustment	(284)			1,029			(470)	7,700
NET (LOSS) INCOME	$ (27,219)	$ 88,505	$ 89,361	$ (8,402)	$ 73,573	$ 86,248	$ 150,647	$ 151,419