Consolidated Statements of Changes in Equity and Comprehensive Income - USD ($) $ in Thousands	Total	Common Stock	Premium on Common Stock	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	Other Comprehensive Income (Loss) of Affiliated Companies	South Jersey Gas Company	South Jersey Gas Company Common Stock	South Jersey Gas Company Premium on Common Stock	South Jersey Gas Company Accumulated Other Comprehensive Loss	South Jersey Gas Company Retained Earnings	South Jersey Gas Company Postretirement Liability Adjustment	[3]	South Jersey Gas Company Unrealized Gain (Loss) on Derivatives-Other	[4]
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)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income (Loss)	(3,490)					(3,490)							72,557				72,557
Other Comprehensive Loss, Net of Tax	(9,384)				(9,384)		(10,920)		1,536		0	0	(11,063)			(11,063)		(11,090)		27
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												122				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)
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)
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
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)
Additional Statement Information [Abstract]
Postretirement Liability Adjustment, tax	4,106												4,164
Reclassification of Unrealized Gain on Derivatives - Other to Net Income, tax	988												19
Net Income (Loss)	17,663					17,663							82,949				82,949
Other Comprehensive Loss, Net of Tax	10,670				10,670		10,636		34		0	0	3,640			3,640		3,606		34
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)
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)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	10,670				10,670		10,636		34		0	0	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)
Additional Statement Information [Abstract]
Postretirement Liability Adjustment, tax	(3,731)												(1,354)
Reclassification of Unrealized Gain on Derivatives - Other to Net Income, tax	12												(12)
Net Income (Loss)	76,917					76,917							87,394				87,394
Other Comprehensive Loss, Net of Tax	(6,463)				(6,463)		(6,498)		35		0	0	(5,518)			(5,518)	0	(5,553)		35
Common Stock Issued or Granted Through Equity Offering or Stock Plans	193,247	8,610	184,634	3
Cash Dividends Declared - Common Stock	(106,938)					(106,938)
Ending balance at Dec. 31, 2019	1,423,785	115,493	1,027,902	(289)	(32,558)	313,237	(32,124)		(327)		(10)	(97)	1,089,898	5,848	355,744	(27,875)	756,181	(27,454)		(421)
Beginning 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)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	(6,463)				(6,463)		(6,498)		35		0	0	(5,518)			(5,518)	0	(5,553)		35
Ending balance at Dec. 31, 2019	1,423,785	$ 115,493	$ 1,027,902	$ (289)	$ (32,558)	$ 313,237	$ (32,124)		$ (327)		$ (10)	$ (97)	1,089,898	$ 5,848	$ 355,744	$ (27,875)	$ 756,181	$ (27,454)		$ (421)
Additional Statement Information [Abstract]
Postretirement Liability Adjustment, tax	2,539												2,241
Reclassification of Unrealized Gain on Derivatives - Other to Net Income, tax	$ 11												$ (11)

[1] These amounts are net of tax of $2,539, $(3,731) and $4,106 for the years ended December 31, 2019, 2018 and 2017, respectively.

[2] These amounts are net of tax of $(11), $(12) and $(988) for the years ended December 31, 2019, 2018 and 2017, respectively.

[3] These amounts are net of tax of $2,241, $(1,354) and $4,164 for the years ended December 31, 2019, 2018 and 2017, respectively.

[4] These amounts are net of tax of $(11), $(12) and $(19) for the years ended December 31, 2019, 2018 and 2017, respectively.