INVESTMENTS IN EQUITY INVESTEES (Details) $ in Thousands	9 Months Ended
	Jun. 30, 2019 USD ($) mi	Sep. 30, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	$ 197,660	$ 190,866
Steckman Ridge
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	115,419	117,001
Total outstanding principal balance of loans	70,400	70,400
PennEast
Schedule of Equity Method Investments [Line Items]
Investments in equity investees	$ 82,241	$ 73,865
Construction plan, project area (in miles) | mi	120