COMMITMENTS AND CONTINGENCIES (Details)			12 Months Ended			468 Months Ended
	Jul. 01, 2018 USD ($)	May 08, 2017 USD ($)	Dec. 31, 2018 USD ($) site decatherm / day contract	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2018 USD ($) site decatherm / day contract	Dec. 31, 2012 USD ($)	Dec. 31, 1996 USD ($)
Commitment and Contingencies [Line Items]
Maximum purchase amount under contract (in dts/d) | decatherm / day			832,500			832,500
Minimum length of contract term			4 years
Maximum length of contract term			10 years
Interest Charges			$ 90,296,000	$ 54,019,000	$ 31,449,000
Accrual for pending litigation			$ 3,200,000	3,000,000		$ 3,200,000
Percentage of workforce that is unionized			45.00%			45.00%
Guarantor obligations			$ 134,600,000			$ 134,600,000
Letter of credit provided			860,000,000			860,000,000
Accrual for Environmental Loss Contingencies [Roll Forward]
Beginning of Year			172,855,000	155,013,000
Accruals			58,706,000	56,405,000		627,100,000
Expenditures			(51,176,000)	(38,563,000)		(373,500,000)
Opening Balance Sheet Adjustment (See Note 20)			73,265,000	0
End of Year			253,650,000	172,855,000	155,013,000	253,650,000
Minimum
Accrual for Environmental Loss Contingencies [Roll Forward]
Environmental remediation costs to clean up SJG's sights			104,600,000
Maximum
Accrual for Environmental Loss Contingencies [Roll Forward]
Environmental remediation costs to clean up SJG's sights			189,800,000
Letters of credit
Commitment and Contingencies [Line Items]
Letter of credit provided			$ 6,100,000.0			$ 6,100,000.0
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								$ 900,000.0
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			$ 500,000.0			$ 500,000.0
Environmental restoration costs | Maximum | Fuel Oil
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs			900,000.0			900,000.0
Parental guarantee
Commitment and Contingencies [Line Items]
Guaranteed Amount			$ 8,600,000			$ 8,600,000
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
South Jersey Resources Group, LLC
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier			$ 5,700,000
South Jersey Resources Group, LLC | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement		$ 57,700,000
Interest Charges			1,000,000
South Jersey Resources Group, LLC | Judicial ruling | Pricing dispute, long-term gas supply contract | Cost of Sales - Nonutility
Commitment and Contingencies [Line Items]
Charges to cost of sales			4,100,000
ETG Utility Operations
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier			4,100,000
South Jersey Gas Company
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier			1,300,000
Interest Charges			28,011,000	24,705,000	17,875,000
Accrual for pending litigation			$ 900,000	700,000		$ 900,000
Percentage of workforce that is unionized			58.00%			58.00%
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			$ 171,696,000	153,047,000
Accruals			21,695,000	55,814,000		$ 499,400,000
Expenditures			(45,320,000)	(37,165,000)		(351,400,000)
End of Year			148,071,000	$ 171,696,000	$ 153,047,000	148,071,000
South Jersey Gas Company | Letters of credit
Commitment and Contingencies [Line Items]
Letters of credit outstanding			6,100,000			6,100,000
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			$ 148,100,000			$ 148,100,000
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			140,000,000			140,000,000
South Jersey Gas Company | Environmental restoration costs | Maximum
Accrual for Environmental Loss Contingencies [Roll Forward]
Estimates of undiscounted future costs			253,700,000			253,700,000
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			246,300,000			$ 246,300,000
South Jersey Gas Company | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement		$ 22,100,000
ETG Utility Operations
Commitment and Contingencies [Line Items]
Minimal annual fee for AMA contract	$ 4,250,000
Regulatory Asset | South Jersey Resources Group, LLC | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement			57,700,000
Regulatory Asset | South Jersey Gas Company | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement			22,400,000
Accounts Payable | South Jersey Resources Group, LLC | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement			57,700,000
Accounts Payable | South Jersey Gas Company | Judicial ruling | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Amount awarded to plaintiff in litigation settlement			$ 22,100,000
Environmental restoration costs | ETG Utility Operations
Commitment and Contingencies [Line Items]
Number of sites for environmental cleanup (in number of sites) | site			6			6