AFFILIATIONS, DISCONTINUED OPERATIONS AND RELATED-PARTY TRANSACTIONS - Narrative (Details) - USD ($)		1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 20, 2020	Dec. 31, 2019	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Schedule of Equity Method Investments [Line Items]
Investment			$ 112,936,000		$ 106,230,000
Notes receivable - affiliate			33,400,000		33,900,000
Net asset - included in investment in affiliates and other noncurrent liabilities			112,900,000		106,200,000
Combined equity contributions and the notes receivable - affiliate			$ 146,300,000		140,100,000
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			$ 93,200,000		91,300,000
Energenic US LLC
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			50.00%
Investment			$ 0
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%
REV | Equity Method Investee
Schedule of Equity Method Investments [Line Items]
Related party notes receivable			$ 19,300,000		19,300,000
Secured Debt
Schedule of Equity Method Investments [Line Items]
Related party notes receivable			$ 11,900,000		$ 12,100,000
Interest rate			7.50%		7.50%
Unsecured promissory notes
Schedule of Equity Method Investments [Line Items]
Notes receivable - affiliate			$ 2,200,000		$ 2,500,000
South Jersey Energy Company | EnergyMark
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			33.00%
South Jersey Energy Company | REV
Schedule of Equity Method Investments [Line Items]
Equity interest (as a percent)			35.00%
SJRG | EnergyMark
Schedule of Equity Method Investments [Line Items]
Total operating revenue, affiliates			$ 7,400,000	$ 5,200,000