COMMON STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 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
Net excess over par value recorded in premium on common stock	$ 0.1
Shares of common stock outstanding (in shares)	79,612,889		79,549,080
Incremental shares included in diluted EPS calculation (in shares)	129,369	121,812
South Jersey Gas Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)	$ 2.50
Shares of common stock outstanding (in shares)	2,339,139