COMMITMENTS AND CONTINGENCIES (Details)	9 Months Ended
	Sep. 30, 2021 USD ($) employee $ / shares	Mar. 22, 2021 $ / shares	Dec. 31, 2020 USD ($) employee	Dec. 31, 2018 $ / shares
Loss Contingencies [Line Items]
Notes receivable related parties current and noncurrent	$ 44,000,000		$ 19,300,000
Number of employees | employee	1,167		1,130
Approximate amount accrued related to all claims	$ 13,600,000		$ 4,100,000
REV LNG
Loss Contingencies [Line Items]
Committed capital contribution	44,000,000		19,300,000
SJG
Loss Contingencies [Line Items]
Approximate amount accrued related to all claims	$ 10,300,000		$ 1,200,000
SJG | Unionized Collective Bargaining Agreements
Loss Contingencies [Line Items]
Number of employees with labor union representation | employee	289		303
Corporate Units | Public Stock Offering
Loss Contingencies [Line Items]
Corporate unit, stated value per share (in dollars per share) | $ / shares	$ 50	$ 50		$ 50
Parental Guarantee
Loss Contingencies [Line Items]
Parental guarantees	$ 10,500,000
Guarantee expiration period	1 year
ETG Utility Operations
Loss Contingencies [Line Items]
Minimum annual fee for long-term asset management agreement	$ 4,250,000
ETG Utility Operations | Unionized Collective Bargaining Agreements
Loss Contingencies [Line Items]
Number of employees with labor union representation | employee	163		167