ACQUISITIONS AND DISPOSITIONS - Net Assets Acquired (Details) - USD ($) $ in Thousands			1 Months Ended	6 Months Ended
	Jan. 13, 2020	Oct. 11, 2019	Nov. 30, 2017	Mar. 31, 2020	Mar. 31, 2019
Business Acquisition [Line Items]
Purchase price				$ 523,647	$ 0
NJR Pipeline | Leaf River Energy Center LLC
Business Acquisition [Line Items]
Purchase price		$ 367,500
Net working capital adjustment		4,111
Transaction costs		1,664
Total costs capitalized		373,275
Identifiable assets acquired
Property, plant and equipment		365,715
Base gas		3,445
Other assets, net		4
Net working capital		4,111
Net assets acquired		$ 373,275
Talen Generation, LLC | Talen's Membership Interests In IEC
Business Acquisition [Line Items]
Purchase price	$ 156,000		$ 10,000
Talen Generation, LLC | Adelphia | Talen's Membership Interests In IEC
Business Acquisition [Line Items]
Purchase price	166,000
Net working capital adjustment	(449)
Transaction costs	9,456
Total costs capitalized	175,007
Identifiable assets acquired
Property, plant and equipment	174,438
Other assets, net	1,018
Net working capital	(449)
Net assets acquired	$ 175,007