AFFILIATIONS, DISCONTINUED OPERATIONS AND RELATED-PARTY TRANSACTIONS - Narrative (Details) - USD ($) $ in Thousands		1 Months Ended	3 Months Ended
	Feb. 20, 2020	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019
Schedule of Equity Method Investments [Line Items]
Investment		$ 87,087	$ 89,952
Investments in unconsolidated affiliates			2,100	$ 2,100
Notes receivable - affiliate		$ 18,100	$ 15,500
Interest accrual on secured notes receivable		7.50%	7.50%
Net asset - included in investment in affiliates and other noncurrent liabilities			$ 90,000
Combined equity contributions and the notes receivable - affiliate			$ 105,500
PennEast Pipeline Company, LLC (PennEast)
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			20.00%
Contract extension to construct pipeline (in years)	2 years	2 years
Investment		$ 82,700	$ 85,000
Energenic US LLC
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			50.00%
Millennium Account Services, LLC
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			50.00%
Potato Creek, LLC (Potato Creek)
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			30.00%
EnerConnex, LLC
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			25.00%
Secured Debt
Schedule of Equity Method Investments [Line Items]
Notes receivable - affiliate		13,100	$ 13,100
Notes receivable, accrued interest, from affiliate		4,400	4,400
Unsecured promissory notes
Schedule of Equity Method Investments [Line Items]
Notes receivable - affiliate		$ 5,000	$ 2,400
South Jersey Energy Company | EnergyMark
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			33.00%
SJRG | EnergyMark
Schedule of Equity Method Investments [Line Items]
Total operating revenue, affiliates			$ 5,200	$ 13,900