COMMON STOCK - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	May 31, 2016	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)	$ 1.25	$ 1.25		$ 1.25
Net excess over par value recorded in premium on common stock				$ 1,100
Shares of common stock issued (in shares)	8,050,000
Shares of common stock outstanding (in shares)		79,549,014		79,549,014		79,478,055
Incremental shares included in diluted EPS calculation (in shares)				136,332	292,782
Antidilutive securities excluded from computation of earnings per share, amount		150,852	297,061
Proceeds from sale of common stock	$ 203,600			$ 0	$ 214,463
Dividend Reinvestment Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Proceeds from sale of common stock					$ 10,800
South Jersey Gas Company
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Par value of common stock (in dollars per share)		$ 2.5		$ 2.5
Shares of common stock outstanding (in shares)		2,339,139		2,339,139