REPORTING SEGMENT AND OTHER OPERATIONS DATA - NET FINANCIAL EARNINGS (LOSS) RECONCILIATION (Details) - USD ($) $ in Thousands	3 Months Ended				6 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2020	Mar. 31, 2019
Segment Reporting [Abstract]
Net financial (loss) earnings	$ 106,936		$ 112,417		$ 147,341	$ 166,510
Less:
Unrealized (gain) loss on derivative instruments and related transactions	(3,773)		10,226		(45,539)	(707)
Tax effect	897		(2,435)		10,828	149
Effects of economic hedging related to natural gas inventory	14,622		22,367		5,735	756
Tax effect	(3,475)		(5,316)		(1,363)	(180)
NFE tax adjustment	10,160		14,002		(186)	6,671
NET INCOME	$ 88,505	$ 89,361	$ 73,573	$ 86,248	$ 177,866	$ 159,821