Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues	$ 345,738	$ 227,127	$ 244,374	$ 425,829	$ 329,981	$ 219,082	$ 154,402	$ 333,035	$ 1,243,068	$ 1,036,500	$ 959,568
Expenses:
Cost of Sales - (Excluding depreciation)	210,585	168,815	179,684	287,143	186,684	142,988	98,340	152,975
Operations, Impairment Charges and Maintenance Including Fixed Charges	152,990	122,617	78,681	85,675	77,858	69,410	71,034	73,042
Income Taxes	(16,498)	(24,765)	(5,544)	21,870	19,266	2,807	(7,189)	39,267	(24,937)	54,151	1,360
Energy and Other Taxes	1,348	1,517	1,551	2,071	1,725	1,449	1,243	1,925	6,487	6,342	6,026
Total Expenses	348,425	268,184	254,372	396,759	285,533	216,654	163,428	267,209
Other Income and Expense	6,696	3,509	2,386	8,677	1,560	7,236	4,228	2,361
Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent	4,009	(37,548)	(7,612)	37,747	46,008	9,664	(4,798)	68,187	(3,404)	119,061	105,610
Loss from Discontinued Operations - (Net of tax benefit)	36	(45)	(47)	(30)	(75)	(29)	(29)	(118)	(86)	(251)	(503)
Net Income (Loss)	$ 4,045	$ (37,593)	$ (7,659)	$ 37,717	$ 45,933	$ 9,635	$ (4,827)	$ 68,069	$ (3,490)	$ 118,810	$ 105,107
Basic Earnings Per Common Share:
Continuing Operations (in USD per share)	$ 0.05	$ (0.47)	$ (0.10)	$ 0.47	$ 0.58	$ 0.12	$ (0.06)	$ 0.96	$ (0.04)	$ 1.56	$ 1.54
Discontinued Operations (in USD per share)	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01
Basic (Loss) Earnings per Common Share (in USD per share)	$ 0.05	$ (0.47)	$ (0.10)	$ 0.47	$ 0.58	$ 0.12	$ (0.06)	$ 0.96	$ (0.04)	$ 1.56	$ 1.53
Average Shares of Common Stock Outstanding - Basic (in shares)	79,549	79,539	79,534	79,519	79,478	79,478	75,298	71,127	79,541	76,362	68,735
Diluted Earnings Per Common Share:
Continuing Operations (in USD per share)	$ 0.05	$ (0.47)	$ (0.10)	$ 0.47	$ 0.58	$ 0.12	$ (0.06)	$ 0.95	$ (0.04)	$ 1.56	$ 1.53
Discontinued Operations (in USD per share)	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.00	0.01
Diluted (Loss) Earnings per Common Share (in USD per share)	$ 0.05	$ (0.47)	$ (0.10)	$ 0.47	$ 0.58	$ 0.12	$ (0.06)	$ 0.95	$ (0.04)	$ 1.56	$ 1.52
Average Shares of Common Stock Outstanding - Diluted (in shares)	79,705	79,539	79,670	79,641	79,643	79,635	75,298	71,416	79,541	76,475	68,931
South Jersey Gas Company
Operating Revenues	$ 170,434	$ 66,755	$ 83,251	$ 196,814	$ 142,502	$ 62,025	$ 68,762	$ 187,766	$ 517,254	$ 461,055	$ 534,290
Expenses:
Cost of Sales - (Excluding depreciation)	68,865	29,499	33,644	72,424	58,695	26,395	19,997	69,303	204,432	174,390	245,290
Operations, Impairment Charges and Maintenance Including Fixed Charges	54,872	47,456	46,656	48,327	47,886	41,303	42,826	46,450
Income Taxes	18,046	(3,688)	1,431	29,911	12,554	(2,007)	1,415	27,404	45,700	39,366	36,945
Energy and Other Taxes	697	865	872	1,295	1,195	838	560	1,027	3,729	3,620	4,031
Total Expenses	142,480	74,132	82,603	151,957	120,330	66,529	64,798	144,184
Other Income and Expense	1,630	1,606	1,618	1,621	727	1,189	1,079	836
Net Income (Loss)	$ 29,584	$ (5,771)	$ 2,266	$ 46,478	$ 22,899	$ (3,315)	$ 5,043	$ 44,418	$ 72,557	$ 69,045	$ 66,578