INVESTMENTS IN EQUITY INVESTEES (Details) $ in Thousands		3 Months Ended
		Dec. 31, 2018 USD ($) mi	Sep. 30, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 192,188	$ 190,866
Steckman Ridge
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	[1]	116,346	117,001
Total outstanding principal balance of loans		70,400	70,400
PennEast
Schedule of Equity Method Investments [Line Items]
Investments in equity investees		$ 75,842	$ 73,865
Construction plan, project area (in miles) | mi		120

[1] Includes loans with a total outstanding principal balance of $70.4 million for both December 31, 2018 and September 30, 2018. The loans accrue interest at a variable rate that resets quarterly and are due October 1, 2023.