INCOME TAXES (Details) - USD ($) $ 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	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes [Line Items]
Annual amortization rate of investment tax credits									3.00%
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at Statutory Rate									$ (9,915)	$ 60,624	$ 37,440
Increase (Decrease) Resulting from:
State Income Taxes									2,778	6,438	3,985
ESOP Dividend									(1,314)	(1,300)	(1,298)
Tax Reform Adjustments									(13,521)	0	0
Amortization of Investment Tax Credits - Utility									0	0	(149)
AFUDC									(3,094)	(900)	(1,109)
Investment and Other Tax Credits									(666)	(10,706)	(37,503)
Other - Net									795	(5)	(6)
Income Taxes: Continuing Operations	$ (16,498)	$ (24,765)	$ (5,544)	$ 21,870	$ 19,266	$ 2,807	$ (7,189)	$ 39,267	(24,937)	54,151	1,360
Income Taxes: Discontinued Operations									(173)	(133)	(257)
Total Income Tax (Benefit) Expense									(25,110)	54,018	1,103
Current:
Federal									(34,971)	0	0
State									(48)	(1,638)	(2,352)
Total Current									(35,019)	(1,638)	(2,352)
Deferred:
Federal									5,761	44,246	(4,622)
State									4,321	11,543	8,483
Total Deferred									10,082	55,789	3,861
Investment Tax Credit - Utility									0	0	(149)
Income Taxes: Continuing Operations	(16,498)	(24,765)	(5,544)	21,870	19,266	2,807	(7,189)	39,267	(24,937)	54,151	1,360
Income Taxes: Discontinued Operations									(173)	(133)	(257)
Deferred Tax Assets:
Net Operating Loss Carryforward												$ 152,541	$ 211,004
Investment and Other Tax Credits												214,605	213,946
Derivatives / Unrealized Gain												2,068	0
Conservation Incentive Program												0	0
Deferred State Tax												16,905	28,833
Gross Up of Excess Deferred Taxes												76,426	0
Pension & Other Post Retirement Benefits												16,624	19,351
Deferred Revenues												5,726	7,669
Provision for Uncollectibles												3,854	5,231
Other												1,949	8,368
Total Deferred Tax Asset												490,698	494,402
Deferred Tax Liabilities:
Book versus Tax Basis of Property												486,854	732,535
Deferred Gas Costs - Net												10,254	2,052
Derivatives / Unrealized Loss												0	1,794
Environmental Remediation												31,393	32,885
Deferred Regulatory Costs												3,554	1,554
Budget Billing - Customer Accounts												4,043	3,347
Deferred Pension & Other Post Retirement Benefits												21,349	34,432
Conservation Incentive Program												7,721	11,846
Equity In Loss Of Affiliated Companies												1,377	3,092
Other												11,037	14,414
Total Deferred Tax Liability												577,582	837,951
Deferred Tax Liability - Net												86,884	343,549
Research and development credits												3,200
Unrecognized tax benefits	1,445			1,445	1,445			559	1,445	559	552	1,445	1,445	$ 559
Accrued interest and penalties on unrecognized tax benefits												800	700	700
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance (beginning)				1,445				559	1,445	559	552
Increase as a result of tax positions taken in prior years									0	886	7
Balance (ending)	1,445				1,445				1,445	1,445	559
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Provisional Income Tax Expense (Benefit)									13,500
Federal
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												586,427
Investment Tax Credit Carryforward												210,013
Alternative minimum tax credits												1,200
Federal | 2030
Deferred Tax Liabilities:
Investment Tax Credit Carryforward												11,628
Federal | 2031
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												163,572
Investment Tax Credit Carryforward												25,664
Federal | 2032
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												42,988
Investment Tax Credit Carryforward												32,031
Federal | 2033
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												56,007
Investment Tax Credit Carryforward												45,606
Federal | 2034
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												105,763
Investment Tax Credit Carryforward												37,699
Federal | 2035
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												49,572
Investment Tax Credit Carryforward												45,005
Federal | 2036
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												72,199
Investment Tax Credit Carryforward												11,744
Federal | 2037
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												96,326
Investment Tax Credit Carryforward												636
State
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												394,666
State | 2031
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												45,866
State | 2032
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												19,356
State | 2033
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												35,271
State | 2034
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												28,853
State | 2035
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												9,956
State | 2036
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												181,189
State | 2037
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												74,175
South Jersey Gas Company
Effective Income Tax Rate Reconciliation, Amount [Abstract]
Tax at Statutory Rate									41,390	37,944	36,233
Increase (Decrease) Resulting from:
State Income Taxes									5,955	4,096	4,584
ESOP Dividend									(1,182)	(1,170)	(1,168)
Amortization of Investment Tax Credits - Utility									0	0	(149)
AFUDC									(1,446)	(900)	(1,109)
Research and Development Credits									0	(613)	(1,400)
Other - Net									983	9	(46)
Income Taxes: Continuing Operations	18,046	(3,688)	1,431	29,911	12,554	(2,007)	1,415	27,404	45,700	39,366	36,945
Current:
Federal									(33,012)	0	0
State									0	(1,614)	(2,203)
Total Current									(33,012)	(1,614)	(2,203)
Deferred:
Federal									69,550	33,064	30,042
State									9,162	7,916	9,255
Total Deferred									78,712	40,980	39,297
Investment Tax Credit - Utility									0	0	(149)
Income Taxes: Continuing Operations	18,046	$ (3,688)	$ 1,431	29,911	12,554	$ (2,007)	$ 1,415	27,404	45,700	39,366	36,945
Deferred Tax Assets:
Net Operating Loss and Tax Credits												73,785	102,290
Deferred State Tax												14,688	24,574
Gross Up of Excess Deferred Taxes												76,426	0
Pension & Other Post Retirement Benefits												15,031	17,264
Deferred Revenues												6,066	7,696
Provision for Uncollectibles												3,811	5,170
Other												2,413	3,573
Total Deferred Tax Asset												192,220	160,567
Deferred Tax Liabilities:
Book versus Tax Basis of Property												386,642	532,330
Deferred Gas Costs - Net												10,254	2,052
Environmental Remediation												31,637	33,573
Deferred Regulatory Costs												3,554	1,554
Budget Billing - Customer Accounts												4,043	3,347
Deferred Pension & Other Post Retirement Benefits												21,349	34,432
Section 461 Prepayments												866	1,147
Conservation Incentive Program												7,721	11,846
Other												6,900	9,694
Total Deferred Tax Liability												472,966	629,975
Deferred Tax Liability - Net												280,746	469,408
Research and development credits												2,700
Unrecognized tax benefits	1,361			1,361	1,361			559	1,361	559	552	1,361	1,361	559
Accrued interest and penalties on unrecognized tax benefits												800	700	$ 700
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance (beginning)				$ 1,361				$ 559	1,361	559	552
Increase as a result of tax positions taken in prior years									0	802	7
Balance (ending)	$ 1,361				$ 1,361				1,361	$ 1,361	$ 559
Tax Cuts And Jobs Act Of 2017, Incomplete Accounting, Change In Tax Rate, Deferred Tax Liability, Provisional Income Tax Expense									$ 263,800
South Jersey Gas Company | Federal
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												261,100	263,000
South Jersey Gas Company | State
Deferred Tax Liabilities:
Net Operating Loss Carryforwards												$ 208,800	$ 80,200