INVESTMENTS IN EQUITY INVESTEES (Details) $ in Thousands		12 Months Ended
		Sep. 30, 2018 USD ($) mi	Sep. 30, 2017 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 190,866	$ 172,585
Steckman Ridge
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	[1]	117,001	120,262
Outstanding principal balance		70,400	70,400
PennEast
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 73,865	$ 52,323
Construction plan, pipeline distance (in miles) | mi		120

[1] Includes loans with a total outstanding principal balance of $70.4 million for both fiscal 2018 and 2017, which accrue interest at a variable rate that resets quarterly and are due October 1, 2023.