COMMON STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)	$ 1.25		$ 1.25
Net excess over par value recorded in premium on common stock			$ 133.4
Shares of common stock outstanding (in shares)	85,506,218		85,506,218		79,549,080
Incremental shares included in diluted EPS calculation (in shares)	1,245,564	138,346	742,313	137,003
SJG Utility Operations
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)	$ 2.50		$ 2.50
Shares of common stock outstanding (in shares)	2,339,139		2,339,139