REPORTING SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS (LOSS) RECONCILIATION (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2021	Dec. 31, 2020	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020
Segment Reporting [Abstract]
Net financial earnings (loss)	$ 170,604		$ 84,291		$ 215,261	$ 119,222
Less:
Unrealized gain on derivative instruments and related transactions	29,255		(3,773)		(8,235)	(45,539)
Tax effect	(6,954)		897		1,958	10,828
Effects of economic hedging related to natural gas inventory	(7,209)		14,622		(14,741)	5,735
Tax effect	1,713		(3,475)		3,503	(1,363)
NFE tax adjustment	3,990		2,174		1,922	(37)
NET INCOME	$ 149,809	$ 81,045	$ 73,846	$ 75,752	$ 230,854	$ 149,598