CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (UNAUDITED) - USD ($) $ in Thousands	Total	SJG	Total South Jersey Industries, Inc. Equity	Common Stock	Common Stock SJG	Premium on Common Stock	Premium on Common Stock SJG	Treasury Stock	AOCL	AOCL SJG	Retained Earnings	Retained Earnings SJG	NCI
Beginning Balance at Dec. 31, 2019	$ 1,423,785	$ 1,089,898		$ 115,493	$ 5,848	$ 1,027,902	$ 355,744	$ (289)	$ (32,558)	$ (27,875)	$ 313,237	$ 756,181
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	101,041	70,522									101,041	70,522
Other Comprehensive Income, Net of Tax	8	8							8	8
Common Stock Issued or Granted Through Equity Offering or Stock Plans	(275)			62		(352)		15
Cash Dividends Declared - Common Stock	(27,276)										(27,276)
Ending Balance at Mar. 31, 2020	1,497,283	1,160,428		115,555	5,848	1,027,550	355,744	(274)	(32,550)	(27,867)	387,002	826,703
Beginning Balance at Dec. 31, 2020	1,666,876	1,303,726	$ 1,660,881	125,740	5,848	1,218,000	465,244	(321)	(38,216)	(31,606)	355,678	864,240	$ 5,995
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	128,727	83,618	128,598								128,598	83,618	129
Other Comprehensive Income, Net of Tax	8	8	8						8	8
Common Stock Issued or Granted Through Equity Offering or Stock Plans	40,303		40,303	2,475		37,771		57
Contract Liability Adjustment (see Note 4)	(62,219)		(62,219)			(62,219)
Cash Dividends Declared - Common Stock	(30,453)		(30,453)								(30,453)
Ending Balance at Mar. 31, 2021	$ 1,743,242	$ 1,387,352	$ 1,737,118	$ 128,215	$ 5,848	$ 1,193,552	$ 465,244	$ (264)	$ (38,208)	$ (31,598)	$ 453,823	$ 947,858	$ 6,124