COMMITMENTS AND CONTINGENCIES (Details) (USD $)	12 Months Ended		420 Months Ended	1 Months Ended
	Dec. 31, 2014 unions sites	Dec. 31, 2013	Dec. 31, 2014 unions sites	Feb. 28, 2011	May 31, 2012	Apr. 30, 2012
Commitment and Contingencies [Line Items]
Long-term Contract for Purchase of Electric Power, Plant Output Being Purchased, Minimum (in dts/d)	633,500		633,500
Long-term Contract for Purchase of Electric Power, Plant Output Being Purchased, Maximum (in dts/d)	921,900		921,900
Long-term Contract for Purchase of Electric Power, Contract Term, Minimum (in years)	3 years
Long-term Contract for Purchase of Electric Power, Contract Term, Maximum (in years)	10 years
Accrual for pending litigation	$ 2,900,000	$ 3,000,000	$ 2,900,000
Collective bargaining agreements [Abstract]
Percentage of personnel represented by collective bargaining agreements (in hundredths)	45.00%		45.00%
Number of unions	2		2
Guarantees [Abstract]
Guarantor Obligations, Current Carrying Value	112,700,000		112,700,000
Liability recorded related to guarantees	600,000		600,000
Maximum amount of obligation under guarantee contracts	4,200,000		4,200,000
Notes receivable - affiliate	14,657,000	8,908,000	14,657,000
Letter of credit provided	610,000,000		610,000,000
Investment in Affiliates	68,351,000	78,273,000	68,351,000
Notes Receivable - Affiliate	36,799,000	39,907,000	36,799,000
Environmental remediation costs [Abstract]
Number of sites for environmental cleanup (in number of sites)	12		12
Site Contingency, Number of Sites Covered By Insurance	11		11
Site Contingency, Insurance Policy Limit	50,000,000		50,000,000
Accrual for Environmental Loss Contingencies [Roll Forward]
Balance, Beginning of Year	123,429,000	112,098,000
Accruals	18,533,000	22,821,000	361,200,000
Expenditures	(13,790,000)	(11,490,000)	(233,100,000)
Balance, End of Year	128,172,000	123,429,000	128,172,000
Letter of Credit, Developer [Member]
Guarantees [Abstract]
Letter of credit provided						5,000,000
Standby Letter of Credit [Member]
Guarantees [Abstract]
Letter of credit provided	13,600,000.0		13,600,000.0
Standby Letter of Credit, Variable-rate Demand Bonds [Member]
Guarantees [Abstract]
Letter of credit provided	87,600,000.0		87,600,000.0
Environmental Restoration Costs [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Loss Contingency, Range of Possible Loss, Minimum	124,300,000		124,300,000
Loss Contingency, Range of Possible Loss, Maximum	223,300,000		223,300,000
Loss Contingency, Range of Possible Loss, Minimum, Assumed By Another Entity	3,200,000		3,200,000
Loss Contingency, Range of Possible Loss, Maximum, Assumed By Another Entity	5,100,000		5,100,000
Environmental Restoration Costs [Member] | Fuel Oil [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Loss Contingency, Range of Possible Loss, Minimum	700,000		700,000
Loss Contingency, Range of Possible Loss, Maximum	1,300,000		1,300,000
Number of Sites Affected By Environmental Remediation	6		6
Environmental Restoration Costs [Member] | Sites Comprising the Majority the Environmental Remediation [Member]
Accrual for Environmental Loss Contingencies [Roll Forward]
Loss Contingency, Range of Possible Loss, Minimum	110,200,000		110,200,000
Loss Contingency, Range of Possible Loss, Maximum	198,400,000		198,400,000
Number of Sites Affected By Environmental Remediation	6		6
ACR Energy Partners LLC [Member]
Guarantees [Abstract]
Equity interest	50.00%		50.00%
Contract with a resort developer (in years)				20 years
LVE Energy Partners [Member]
Guarantees [Abstract]
Liability recorded related to guarantees		800,000
Notes receivable - affiliate	8,800,000		8,800,000
Energenic [Member]
Guarantees [Abstract]
Liability recorded related to guarantees	400,000		400,000
Equity interest	50.00%		50.00%
Investment in Affiliates	17,000,000		17,000,000
Notes Receivable - Affiliate	13,900,000		13,900,000
Energenic [Member] | UMM Energy Partners, LLC [Member]
Capital contribution obligation [Abstract]
Contract Term					30 years
Energenic [Member] | UMM Energy Partners, LLC [Member] | Maximum [Member]
Capital contribution obligation [Abstract]
Annual Obligations Under the Agreement	2,400,000.0
Parental Guarantee [Member]
Capital contribution obligation [Abstract]
Guaranteed amount	6,400,000		6,400,000
South Jersey Resources Group, Llc [Member]
Commitment and Contingencies [Line Items]
Long-term Contract for Purchase of Electric Power, Monthly Fees Paid to Supplier	500,000
South Jersey Gas Company [Member]
Commitment and Contingencies [Line Items]
Long-term Contract for Purchase of Electric Power, Monthly Fees Paid to Supplier	3,900,000
Guarantees [Abstract]
Letter of credit provided	$ 210,000,000		$ 210,000,000