INVESTMENTS IN EQUITY INVESTEES - SCHEDULE OF EQUITY METHOD INVESTMENTS (Details) $ in Thousands		9 Months Ended
		Jun. 30, 2015 USD ($) mi	Sep. 30, 2014 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 151,923	$ 153,010
Steckman Ridge [Member]
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	[1]	126,037	128,413
Steckman Ridge [Member] | Equity Method Investee [Member]
Schedule of Equity Method Investments [Line Items]
Outstanding principal balance		70,400	70,400
Iroquois [Member]
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		23,006	24,042
PennEast [Member]
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 2,880	$ 555
Construction plan, project area (in miles) | mi		115

[1] Includes loans with a total outstanding principal balance of $70.4 million for both June 30, 2015 and September 30, 2014. The loans accrue interest at a variable rate that resets quarterly and are due October 1, 2023.