BUSINESS SEGMENT AND OTHER OPERATIONS DATA, NET FINANCIAL EARNINGS LOSS RECONCILIATION (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2014
Segment Reporting [Abstract]
Consolidated net financial earnings									$ 138,085	$ 151,503	$ 176,857
Less:
Unrealized loss (gain) on derivative instruments and related transactions									46,883	(38,681)	28,534
Unrealized Gain (Loss) on Derivatives and Commodity Contracts, Tax									(17,018)	14,391	(10,492)
Effects of economic hedging related to natural gas inventory									(36,816)	(8,225)	26,639
Tax effect									13,364	3,058	(9,794)
Net income, as reported	$ 25,400	$ (17,363)	$ 73,354	$ 50,281	$ 4,197	$ (7,460)	$ 60,903	$ 123,320	$ 131,672	$ 180,960	$ 141,970