REVENUES - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) project	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Disaggregation of Revenue [Line Items]
Total revenues from alternative revenue programs	$ 38.1	$ 29.0	$ 13.8
SJG Utility Operations
Disaggregation of Revenue [Line Items]
Total revenues from alternative revenue programs	$ 28.0	$ 34.8	$ 16.9
Marina Energy LLC
Disaggregation of Revenue [Line Items]
Number of solar energy projects | project	6