COMMITMENTS AND CONTINGENCIES (Details)		3 Months Ended		27 Months Ended
	Jul. 01, 2018 USD ($)	Mar. 31, 2019 USD ($) site decatherm / day contract	Mar. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) site decatherm / day contract	Dec. 31, 2018 USD ($)	Apr. 30, 2018 $ / shares
Commitment and Contingencies [Line Items]
Minimum annual fee for long-term asset management contract	$ 4,250,000
Percentage of personnel represented by collective bargaining agreements		45.00%		45.00%
Interest charges		$ 28,653,000	$ 13,972,000
Approximate amount accrued related to all claims		$ 3,100,000		$ 3,100,000	$ 3,200,000
Pricing dispute, long-term gas supply contract
Commitment and Contingencies [Line Items]
Number of long-term gas supply contracts | contract		2		2
Line of Credit
Commitment and Contingencies [Line Items]
Letter of credit provided		$ 860,000,000		$ 860,000,000
Standby letters of credit
Commitment and Contingencies [Line Items]
Letter of credit provided		10,600,000.0		$ 10,600,000.0
SJG Utility Operations
Commitment and Contingencies [Line Items]
Cumulative obligation for demand charges and reservation fees per month		$ 6,800,000
Percentage of personnel represented by collective bargaining agreements		65.00%		65.00%
Charges to cost of sales		$ 118,880,000	89,808,000
Interest charges		$ 7,848,000	6,728,000
Approximate amount accrued related to all claims					$ 900,000
SJG Utility Operations | Environmental restoration costs
Commitment and Contingencies [Line Items]
Number of sites for environmental cleanup | site		12		12
SJG Utility Operations | Pricing dispute, long-term gas supply contract | Judicial ruling
Commitment and Contingencies [Line Items]
Amount to be paid to supplier				$ 22,400,000
SJG Utility Operations | Line of Credit
Commitment and Contingencies [Line Items]
Letter of credit provided		$ 210,000,000		210,000,000
SJG Utility Operations | Line of Credit | Line of Credit
Commitment and Contingencies [Line Items]
Letters of credit outstanding		800,000		800,000
SJG Utility Operations | Letters of credit under separate facility
Commitment and Contingencies [Line Items]
Letter of credit provided		25,100,000.0		$ 25,100,000.0
South Jersey Resources Group
Commitment and Contingencies [Line Items]
Cumulative obligation for demand charges and reservation fees per month		$ 1,300,000
Maximum purchase commitment (in dts/d) | decatherm / day		832,500		832,500
Minimum length of contract		4 years
Maximum length of contract		10 years
South Jersey Resources Group | Pricing dispute, long-term gas supply contract | Judicial ruling
Commitment and Contingencies [Line Items]
Amount to be paid to supplier				$ 58,200,000
Interest charges		$ 400,000	200,000
Accounts Payable | SJG Utility Operations | Pricing dispute, long-term gas supply contract | Judicial ruling
Commitment and Contingencies [Line Items]
Amount to be paid to supplier				22,400,000
Accounts Payable | South Jersey Resources Group | Pricing dispute, long-term gas supply contract | Judicial ruling
Commitment and Contingencies [Line Items]
Amount to be paid to supplier				58,200,000
Capital Units
Commitment and Contingencies [Line Items]
Corporate Unit, stated value per share (in dollars per share) | $ / shares						$ 50
Parental guarantee
Commitment and Contingencies [Line Items]
Parental guarantees		$ 9,210,000.00		$ 9,210,000.00
Guarantee expiration period		2 years
Elizabethtown Gas
Commitment and Contingencies [Line Items]
Cumulative obligation for demand charges and reservation fees per month		$ 4,100,000
Minimum annual fee for long-term asset management contract		$ 4,250,000
Elizabethtown Gas | Environmental restoration costs
Commitment and Contingencies [Line Items]
Number of sites for environmental cleanup | site		6		6
Nonutility Operations
Commitment and Contingencies [Line Items]
Charges to cost of sales		$ 213,938,000	$ 195,951,000
Nonutility Operations | South Jersey Resources Group | Pricing dispute, long-term gas supply contract | Judicial ruling
Commitment and Contingencies [Line Items]
Charges to cost of sales		$ 100,000