Consolidated Statements of Changes in Equity and Comprehensive Income - USD ($) $ in Thousands	Total	Common Stock	Premium on Common Stock/Other Paid-In-Capital	Treasury Stock	Accumulated Other Comprehensive Loss	Retained Earnings	Postretirement Liability Adjustment	[1]	Unrealized Gain (Loss) on Derivatives-Other	[2]	Unrealized Gain (Loss) on Available- for-Sale Securities	[2]	Other Comprehensive Income (Loss) of Affiliated Companies	[2]	South Jersey Gas Company	South Jersey Gas Company Common Stock	South Jersey Gas Company Premium on Common Stock/Other Paid-In-Capital	South Jersey Gas Company Accumulated Other Comprehensive Loss	South Jersey Gas Company Retained Earnings	South Jersey Gas Company Postretirement Liability Adjustment	[1]	South Jersey Gas Company Unrealized Gain (Loss) on Derivatives-Other	[3]	South Jersey Gas Company Unrealized Gain (Loss) on Available- for-Sale Securities	[3]	Postretirement Liability	Postretirement Liability South Jersey Gas Company	Unrealized Gain (Loss)	Unrealized Gain (Loss) South Jersey Gas Company
Beginning balance at Dec. 31, 2015	$ 1,037,539	$ 88,707	$ 499,460	$ (296)	$ (24,499)	$ 474,167	$ (22,145)		$ (2,129)		$ (128)		$ (97)		$ 707,927	$ 5,848	$ 250,827	$ (12,862)	$ 464,114	$ (12,220)		$ (544)		$ (98)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	118,810					118,810									69,045				69,045
Common Stock Issued or Granted Through Equity Offering or Stock Plans	218,153	10,640	207,483	30
Cash Dividends Declared – Common Stock	(82,380)					(82,380)
Additional Investment by Shareholder															65,000		65,000
Ending balance at Dec. 31, 2016	1,289,240	99,347	706,943	(266)	(27,381)	510,597	(25,342)		(1,932)		(10)		(97)		839,900	5,848	315,827	(14,934)	533,159	(14,417)		(517)		0
Beginning balance at Dec. 31, 2015	1,037,539	88,707	499,460	(296)	(24,499)	474,167	(22,145)		(2,129)		(128)		(97)		707,927	5,848	250,827	(12,862)	464,114	(12,220)		(544)		(98)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	(2,882)				(2,882)		(3,197)		197		118		0		(2,072)			(2,072)		(2,197)		27		98
Ending balance at Dec. 31, 2016	1,289,240	99,347	706,943	(266)	(27,381)	510,597	(25,342)		(1,932)		(10)		(97)		839,900	5,848	315,827	(14,934)	533,159	(14,417)		(517)		0
Additional Statement Information [Abstract]
Combined average statutory tax rate																										40.00%	40.00%	40.00%	40.00%
Net Income	(3,490)					(3,490)									72,557				72,557
Common Stock Issued or Granted Through Equity Offering or Stock Plans	2,799	89	2,715	(5)
Cash Dividends Declared – Common Stock	(87,308)					(87,308)									(20,000)				(20,000)
Additional Investment by Shareholder															40,000		40,000
Excess Tax Benefit	552					552									122		0		122
Tax Deficiency from Restricted Stock Plan															(83)		(83)
Ending balance at Dec. 31, 2017	1,192,409	99,436	709,658	(271)	(36,765)	420,351	(36,262)		(396)		(10)		(97)		921,433	5,848	355,744	(25,997)	585,838	(25,507)		(490)		0
Beginning balance at Dec. 31, 2016	1,289,240	99,347	706,943	(266)	(27,381)	510,597	(25,342)		(1,932)		(10)		(97)		839,900	5,848	315,827	(14,934)	533,159	(14,417)		(517)		0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	(9,384)				(9,384)		(10,920)		1,536		0		0		(11,063)			(11,063)		(11,090)		27		0
Ending balance at Dec. 31, 2017	1,192,409	99,436	709,658	(271)	(36,765)	420,351	(36,262)		(396)		(10)		(97)		921,433	5,848	355,744	(25,997)	585,838	(25,507)		(490)		0
Additional Statement Information [Abstract]
Combined average statutory tax rate																										27.00%	27.00%	39.00%	39.00%
Net Income	17,663					17,663									82,949				82,949
Common Stock Issued or Granted Through Equity Offering or Stock Plans	141,036	7,447	133,610	(21)
Cash Dividends Declared – Common Stock	(94,756)					(94,756)
Ending balance at Dec. 31, 2018	1,267,022	106,883	843,268	(292)	(26,095)	343,258	(25,626)		(362)		(10)		(97)		1,008,022	5,848	355,744	(22,357)	668,787	(21,901)		(456)		0
Beginning balance at Dec. 31, 2017	1,192,409	99,436	709,658	(271)	(36,765)	420,351	(36,262)		(396)		(10)		(97)		921,433	5,848	355,744	(25,997)	585,838	(25,507)		(490)		0
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	10,670				10,670		10,636		34						3,640			3,640		3,606		34
Ending balance at Dec. 31, 2018	$ 1,267,022	$ 106,883	$ 843,268	$ (292)	$ (26,095)	$ 343,258	$ (25,626)		$ (362)		$ (10)		$ (97)		$ 1,008,022	$ 5,848	$ 355,744	$ (22,357)	$ 668,787	$ (21,901)		$ (456)		$ 0
Additional Statement Information [Abstract]
Combined average statutory tax rate																										25.00%	25.00%	25.00%	25.00%

[1] Determined using a combined average statutory tax rate of 25% in 2018; 27% for 2017; and 40% for 2016.

[2] Determined using a combined average statutory tax rate of 25% for 2018; 39% for 2017; and 40% for 2016.

[3] Determined using a combined average statutory tax rate of 25% for 2018; 39% for 2017; and 40% for 2016.