INCOME TAXES AND CREDITS (Details) (USD $)	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Tax Expense (Benefit), Continuing Operations, Income Tax Reconciliation [Abstract]
Tax at Statutory Rate									$ 32,183,000	$ 30,510,000	$ 25,760,000
Increase (Decrease) Resulting from:
State Income Taxes									5,302,000	5,316,000	4,340,000
Amortization of Investment Tax Credits									(287,000)	(302,000)	(310,000)
ESOP Dividend									(1,027,000)	(956,000)	(874,000)
AFUDC									(1,048,000)	(729,000)	0
Amortization of Flowthrough Depreciation									0	526,000	664,000
Other - Net									(1,412,000)	(84,000)	98,000
Net Income Taxes	10,589,000	258,000	1,887,000	20,977,000	11,869,000	(699,000)	1,065,000	22,046,000	33,711,000	34,281,000	29,678,000
Current:
Federal									(4,635,000)	(924,000)	399,000
State									(7,000)	168,000	4,739,000
Total Current									(4,642,000)	(756,000)	5,138,000
Deferred:
Federal									30,477,000	27,329,000	22,912,000
State									8,163,000	8,010,000	1,938,000
Total Deferred									38,640,000	35,339,000	24,850,000
Investment Tax Credits									(287,000)	(302,000)	(310,000)
Net Income Taxes	10,589,000	258,000	1,887,000	20,977,000	11,869,000	(699,000)	1,065,000	22,046,000	33,711,000	34,281,000	29,678,000
Annual amortization rate of investment tax credits									3.00%
Current:
Current Deferred Tax (Asset) Liability - Net	10,432,000				(6,301,000)				10,432,000	(6,301,000)
Noncurrent:
Noncurrent Deferred Tax Liability – Net	310,357,000				285,159,000				310,357,000	285,159,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at January 1,				421,000				478,000	421,000	478,000	576,000
Increase as a result of tax position taken in prior years									82,000	119,000	0
Decrease due to a lapse in the statue of limitations									0	(90,000)	0
Settlements									0	(86,000)	(98,000)
Balance at December 31,	503,000				421,000				503,000	421,000	478,000
Accrued interest and penalties on unrecognized tax benefits	600,000				600,000				600,000	600,000	600,000
Internal Revenue Service (IRS) [Member]
Noncurrent:
Operating loss carryforwards	104,700,000								104,700,000
Internal Revenue Service (IRS) [Member] | 2031 [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax Credit Carryforward, Amount	100,400,000								100,400,000
Internal Revenue Service (IRS) [Member] | 2032 [Member]
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Tax Credit Carryforward, Amount	4,300,000								4,300,000
State and Local Jurisdiction [Member]
Noncurrent:
Operating loss carryforwards	16,600,000								16,600,000
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	1,300,000								1,300,000
SJI [Member] | Prepaid Taxes [Member]
Noncurrent:
Income taxes due from parent company	4,600,000				1,000,000				4,600,000	1,000,000
Classified as Current [Member]
Current:
Net Operating Loss Carryforward	(2,586,000)				(6,600,000)				(2,586,000)	(6,600,000)
Budget Billing - Customer Accounts	1,033,000				(4,261,000)				1,033,000	(4,261,000)
Provision for Uncollectibles	(1,409,000)				(970,000)				(1,409,000)	(970,000)
Conservation Incentive Program	13,942,000				5,975,000				13,942,000	5,975,000
Section 461 Prepayments	930,000				822,000				930,000	822,000
Other	(1,478,000)				(1,267,000)				(1,478,000)	(1,267,000)
Classified as Noncurrent [Member]
Current:
Net Operating Loss Carryforward	(35,901,000)				(35,943,000)				(35,901,000)	(35,943,000)
Noncurrent:
Book Versus Tax Basis of Property	323,470,000				290,882,000				323,470,000	290,882,000
Deferred Fuel Costs - Net	3,325,000				12,005,000				3,325,000	12,005,000
Environmental Remediation	17,643,000				19,869,000				17,643,000	19,869,000
Deferred Regulatory Costs	15,374,000				7,396,000				15,374,000	7,396,000
Deferred State Tax	(15,106,000)				(13,219,000)				(15,106,000)	(13,219,000)
Investment Tax Credit Basis Gross-Up	(318,000)				(466,000)				(318,000)	(466,000)
Deferred Pension & Other Post Retirement Benefits	39,174,000				36,048,000				39,174,000	36,048,000
Pension & Other Post Retirement Benefits	(28,846,000)				(24,380,000)				(28,846,000)	(24,380,000)
Deferred Revenues	(8,922,000)				(7,899,000)				(8,922,000)	(7,899,000)
Other	$ 464,000				$ 866,000				$ 464,000	$ 866,000