SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - INVESTMENTS IN EQUTIY SECURITIES (Details) shares in Thousands, $ in Thousands			3 Months Ended	6 Months Ended
	Mar. 06, 2019 USD ($)	Jan. 28, 2019 shares	Mar. 31, 2019 USD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)	Sep. 30, 2018 USD ($)
Schedule of Equity Method Investments [Line Items]
Investments in equity securities						$ 32,900
Debt conversion ratio		0.2492
Proceeds from sale of investments in equity securities, net	$ 34,500			$ 34,484	$ 6,616
Pre-tax again investments in equity securities			$ 1,300	$ 1,600
Common Units
Schedule of Equity Method Investments [Line Items]
Other ownership interests, units issued (in units) | shares		1,840
Dominion Shares
Schedule of Equity Method Investments [Line Items]
Other ownership interests, units issued (in units) | shares		458