INVESTMENTS IN EQUITY INVESTEES (Details) $ in Thousands	12 Months Ended
	Sep. 30, 2017 USD ($) mi	Sep. 30, 2016 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	$ 172,585	$ 141,148
Steckman Ridge
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	120,262	123,155
Steckman Ridge | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Outstanding principal balance	70,400	70,400
PennEast
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	$ 52,323	$ 17,993
Construction plan, pipeline distance (in miles) | mi	120