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 (A)		Unrealized Gain (Loss) on Derivatives-Other (B)	[2]	Unrealized Gain (Loss) on Available- for-Sale Securities (B)	[2]	Other Comprehensive Income (Loss) of Affiliated Companies (B)	[2]	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 (A)		South Jersey Gas Company Unrealized Gain (Loss) on Derivatives-Other (B)	[3]	South Jersey Gas Company Unrealized Gain (Loss) on Available- for-Sale Securities (B)	[3]	Post-Retirement Liability	Post-Retirement Liability South Jersey Gas Company	Unrealized Gain (Loss)	Unrealized Gain (Loss) South Jersey Gas Company
Balance at Dec. 31, 2014	$ 932,432	$ 85,418	$ 438,384	$ (330)	$ (30,258)	$ 439,218									$ 680,568		$ 5,848	$ 250,899	$ (14,479)		$ 438,300
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	105,107					105,107									66,578						66,578
Common Stock Issued or Granted Under Stock Plans	64,399	3,289	61,076	34
Cash Dividends Declared - Common Stock	(70,158)					(70,158)									(40,764)						(40,764)
Additional Investment by Shareholder															0			0
Tax Deficiency from Restricted Stock Plan															(72)			(72)
Balance at Dec. 31, 2015	1,037,539	88,707	499,460	(296)	(24,499)	474,167									707,927		5,848	250,827	(12,862)		464,114
Additional Statement Information [Abstract]
Combined average statutory tax rate																												40.00%	40.00%	40.00%	40.00%
Balance at January 1 at Dec. 31, 2014					(30,258)		$ (27,663)	[1]	$ (2,450)		$ (75)		$ (70)						(14,479)			$ (13,837)	[1]	$ (567)		$ (75)
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	5,759				5,759		5,518	[1]	321		(53)		(27)		1,617	[1]			1,617	[1]		1,617	[1]	23		(23)
Balance at December 31 at Dec. 31, 2015					(24,499)		(22,145)	[1]	(2,129)		(128)		(97)						(12,862)			(12,220)	[1]	(544)		(98)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net Income	118,810					118,810									69,045						69,045
Common Stock Issued or Granted Under Stock Plans	218,153	10,640	207,483	30
Cash Dividends Declared - Common Stock	(82,380)					(82,380)									0						0
Additional Investment by Shareholder															65,000			65,000
Tax Deficiency from Restricted Stock Plan															0			0
Balance at Dec. 31, 2016	1,289,240	99,347	706,943	(266)	(27,381)	510,597	(25,342)								839,900		5,848	315,827	(14,934)		533,159	(14,417)
Additional Statement Information [Abstract]
Combined average statutory tax rate																												40.00%	40.00%	40.00%	40.00%
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	(2,882)				(2,882)		(3,197)	[1]	197		118		0		(2,072)				(2,072)			(2,197)	[1]	27		98
Balance at December 31 at Dec. 31, 2016	(27,381)				(27,381)		(25,342)	[1]	(1,932)		(10)		(97)		(14,934)				(14,934)			(14,417)	[1]	(517)		0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Excess tax benefit - See Footnote 1															122
Net Income	(3,490)					(3,490)									72,557						72,557
Common Stock Issued or Granted Under 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
Tax Deficiency from Restricted Stock Plan															(83)			(83)
Balance at Dec. 31, 2017	1,192,409	$ 99,436	$ 709,658	$ (271)	(36,765)	420,351	(36,262)								921,433		$ 5,848	$ 355,744	(25,997)		585,838	(25,507)
Additional Statement Information [Abstract]
Combined average statutory tax rate																												27.00%	27.00%	39.00%	39.00%
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Changes During Year	(9,384)				(9,384)		(10,920)	[1]	1,536		0		0		(11,063)				(11,063)			(11,090)	[1]	27		0
Balance at December 31 at Dec. 31, 2017	(36,765)				$ (36,765)		$ (36,262)	[1]	$ (396)		$ (10)		$ (97)		$ (25,997)				$ (25,997)			$ (25,507)	[1]	$ (490)		$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Excess tax benefit - See Footnote 1	$ 552					$ 552															$ 122

[1] Determined using a combined average statutory tax rate of 27% for 2017 and 40% for 2016 and 2015.

[2] Determined using a combined average statutory tax rate of 39% for 2017 and 40% for 2016 and 2015.

[3] Determined using a combined average statutory tax rate of 39% for 2017 and 40% for 2016 and 2015.