COMMITMENTS AND CONTINGENCIES (Details)		1 Months Ended		12 Months Ended			456 Months Ended
	May 08, 2017 USD ($)	Nov. 30, 2017 USD ($)	May 31, 2017 USD ($)	Dec. 31, 2017 USD ($) site decatherm / day contract	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) site decatherm / day contract	Dec. 31, 2012 USD ($)	Dec. 31, 1996 USD ($)
Commitment and Contingencies [Line Items]
Minimum purchase amount under contract (in dts/d) | decatherm / day				604,000			604,000
Maximum purchase amount under contract (in dts/d) | decatherm / day				954,000			954,000
Minimum length of contract term				3 years
Maximum length of contract term				10 years
Cost of Sales - Nonutility				$ 646,567,000	$ 413,833,000	$ 319,579,000
Interest Charges				$ 54,019,000	31,449,000	31,622,000
Capacity management contract, term				3 years
Accrual for pending litigation				$ 3,000,000	3,100,000		$ 3,000,000
Percentage of workforce that is unionized				39.00%			39.00%
Guarantor obligations				$ 95,700,000			$ 95,700,000
Letter of credit provided				660,000,000			660,000,000
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning of Year				155,013,000	126,623,000
Accruals				56,405,000	60,713,000		490,700,000
Expenditures				(38,563,000)	(32,323,000)		(317,900,000)
End of Year				172,855,000	155,013,000	126,623,000	172,855,000
Letters of credit
Commitment and Contingencies [Line Items]
Letter of credit provided				$ 6,600,000.0			$ 6,600,000.0
Environmental restoration costs
Accrual for Environmental Loss Contingencies [Roll Forward]
EMI's assumed responsibility for environment liabilities, minimum									$ 500,000.0
EMI's assumed responsibility for environment liabilities, maximum									$ 1,000,000.0
Environmental restoration costs | Fuel Oil
Accrual for Environmental Loss Contingencies [Roll Forward]
Number of sites affected by environmental remediation | site				5			5
Environmental restoration costs | Minimum | Fuel Oil
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				$ 600,000.0			$ 600,000.0
Environmental restoration costs | Maximum | Fuel Oil
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				1,100,000.0			1,100,000.0
Parental guarantee
Commitment and Contingencies [Line Items]
Guaranteed Amount				$ 6,000,000			$ 6,000,000
Contract term				2 years
Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Number of long-term gas supply contracts | contract				2			2
Settled litigation | Dispute, long-term supply contract
Commitment and Contingencies [Line Items]
Cost of Sales - Nonutility		$ 7,400,000
Interest Charges		1,900,000
Litigation Settlement, Amount Awarded from Other Party		$ 9,300,000
South Jersey Resources Group, LLC
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier				$ 1,300,000
South Jersey Resources Group, LLC | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	$ 53,600,000
Cost of Sales - Nonutility				49,600,000
Interest Charges				4,000,000
South Jersey Resources Group, LLC | Pending litigation | Dispute, long-term management contract
Commitment and Contingencies [Line Items]
Damages sought				13,300,000
South Jersey Resources Group, LLC | Settled litigation | Dispute, long-term management contract
Commitment and Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party				9,500,000
South Jersey Gas Company
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier				6,000,000
Interest Charges				24,705,000	17,875,000	19,906,000
Accrual for pending litigation				$ 700,000	600,000		$ 700,000
Percentage of workforce that is unionized				56.00%			56.00%
Letter of credit provided				$ 210,000,000			$ 210,000,000
Letters of credit outstanding				$ 800,000			$ 800,000
Number of sites for environmental cleanup (in number of sites) | site				12			12
Number of sites covered by insurance | site				11			11
Insurance policy limit								$ 50,000,000
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning of Year				$ 153,047,000	123,194,000
Accruals				55,814,000	61,933,000		$ 473,300,000
Expenditures				(37,165,000)	(32,080,000)		(301,600,000)
End of Year				171,696,000	$ 153,047,000	$ 123,194,000	171,696,000
South Jersey Gas Company | Letters of credit
Commitment and Contingencies [Line Items]
Letters of credit outstanding				6,600,000			6,600,000
South Jersey Gas Company | Variable-rate demand bonds
Commitment and Contingencies [Line Items]
Letter of credit provided				$ 25,100,000.0			$ 25,100,000.0
South Jersey Gas Company | Environmental restoration costs | Majority of the environmental remediation
Accrual for Environmental Loss Contingencies [Roll Forward]
Number of sites affected by environmental remediation | site				6			6
South Jersey Gas Company | Environmental restoration costs | Minimum
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				$ 171,700,000			$ 171,700,000
South Jersey Gas Company | Environmental restoration costs | Minimum | Majority of the environmental remediation
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				158,200,000			158,200,000
South Jersey Gas Company | Environmental restoration costs | Maximum
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				284,100,000			284,100,000
South Jersey Gas Company | Environmental restoration costs | Maximum | Majority of the environmental remediation
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs				275,700,000			275,700,000
South Jersey Gas Company | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Litigation Settlement, Amount Awarded to Other Party	$ 20,400,000
Marina Energy LLC | Unsecured debt
Commitment and Contingencies [Line Items]
Amount of debt retired			$ 62,300,000
Elizabethtown Gas and Elkton Gas
Accrual for Environmental Loss Contingencies [Roll Forward]
Liabilities arising from contingencies, amount recognized				$ 80,500,000			$ 80,500,000