COMMITMENTS AND CONTINGENCIES (Details)	12 Months Ended		444 Months Ended
	Dec. 31, 2016 USD ($) site union decatherm / day contract	Dec. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) site union decatherm / day contract	Sep. 30, 2016 USD ($)	Dec. 31, 2012 USD ($)	Dec. 31, 1996 USD ($)
Commitment and Contingencies [Line Items]
Minimum purchase amount under contract (in dts/d) | decatherm / day	745,000		745,000
Maximum purchase amount under contract (in dts/d) | decatherm / day	940,000		940,000
Minimum length of contract term	3 years
Maximum length of contract term	10 years
Capacity management contract, term	3 years
Accrual for pending litigation	$ 3,100,000	$ 3,200,000	$ 3,100,000
Percentage of workforce that is unionized	45.00%		45.00%
Number of unions with collective bargaining agreements | union	2		2
Guarantor obligations	$ 125,400,000		$ 125,400,000
Letter of credit provided	660,000,000		660,000,000	$ 50,000,000
Letters of credit outstanding	$ 4,800,000		$ 4,800,000
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	$ 126,623,000	128,172,000
Accruals	60,713,000	19,489,000	$ 437,100,000
Expenditures	(32,323,000)	(21,038,000)	(282,100,000)
End of Year	155,013,000	$ 126,623,000	155,013,000
Letters of credit
Commitment and Contingencies [Line Items]
Letter of credit provided	4,800,000.0		4,800,000.0
Variable-rate demand bonds
Commitment and Contingencies [Line Items]
Letter of credit provided	$ 87,500,000.0		$ 87,500,000.0
Environmental restoration costs
Commitment and Contingencies [Line Items]
EMI's assumed responsibility for environment liabilities, minimum						$ 1,300,000.0
EMI's assumed responsibility for environment liabilities, maximum						$ 2,100,000.0
Environmental restoration costs | Fuel Oil
Commitment and Contingencies [Line Items]
Number of sites affected by environmental remediation | site	5		5
Environmental restoration costs | Majority of the environmental remediation
Commitment and Contingencies [Line Items]
Number of sites affected by environmental remediation | site	6		6
Environmental restoration costs | Minimum
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	$ 153,000,000		$ 153,000,000
Environmental restoration costs | Minimum | Fuel Oil
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	700,000.0		700,000.0
Environmental restoration costs | Minimum | Majority of the environmental remediation
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	141,200,000		141,200,000
Environmental restoration costs | Maximum
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	257,100,000		257,100,000
Environmental restoration costs | Maximum | Fuel Oil
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	1,300,000.0		1,300,000.0
Environmental restoration costs | Maximum | Majority of the environmental remediation
Commitment and Contingencies [Line Items]
Estimates of undiscounted future costs	246,700,000		246,700,000
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
South Jersey Resources Group, LLC
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier	$ 500,000
South Jersey Resources Group, LLC | Pending litigation | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Damages sought	40,200,000
South Jersey Resources Group, LLC | Pending litigation | Dispute, long-term management contract
Commitment and Contingencies [Line Items]
Damages sought	13,300,000
South Jersey Gas Company
Commitment and Contingencies [Line Items]
Amount of monthly fees paid to supplier	5,600,000
Letter of credit provided	210,000,000		$ 210,000,000
South Jersey Gas Company | Letters of credit
Commitment and Contingencies [Line Items]
Letters of credit outstanding	800,000		$ 800,000
South Jersey Gas Company | Pending litigation | Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Damages sought	$ 14,900,000