REVENUE - Receivables and Unbilled Revenue (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Billed Revenues
Disaggregation of Revenue [Line Items]
Contracts with customers, asset	$ 253,661	$ 337,502	$ 202,379
Increase (Decrease) in contracts with customers, asset	(83,841)	135,123
Unbilled Revenue
Disaggregation of Revenue [Line Items]
Contracts with customers, asset	84,821	79,538	73,377
Increase (Decrease) in contracts with customers, asset	5,283	6,161
SJG Utility Operations | Billed Revenues
Disaggregation of Revenue [Line Items]
Contracts with customers, asset	84,940	101,572	78,571
Increase (Decrease) in contracts with customers, asset	(16,632)	23,001
SJG Utility Operations | Unbilled Revenue
Disaggregation of Revenue [Line Items]
Contracts with customers, asset	45,016	43,271	$ 54,980
Increase (Decrease) in contracts with customers, asset	$ 1,745	$ (11,709)