LINES OF CREDIT (Details)	1 Months Ended	9 Months Ended
	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Sep. 23, 2019 USD ($)	May 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Amount Outstanding During Period		$ 882,700,000	$ 516,900,000
Unsecured Debt
Line of Credit Facility [Line Items]
Principal amount issued				$ 100,000,000.0
SJI | Unsecured Debt
Line of Credit Facility [Line Items]
Principal amount issued				$ 100,000,000
SJG
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Amount Outstanding During Period		175,300,000	$ 141,100,000
Commercial Paper and Letters of Credit | SJG | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility		200,000,000
Line of Credit
Line of Credit Facility [Line Items]
Total Facility		$ 1,060,000,000
Debt covenant, ratio of indebtedness to total capitalization, syndicate		0.70
Weighted average interest rate on borrowings		3.00%	2.68%
Average borrowings outstanding		$ 487,800,000	$ 258,800,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum aggregate letters of credit allowed		50,000,000.0
Line of Credit | SJI
Line of Credit Facility [Line Items]
Total Facility		650,000,000
Line of Credit | SJI | Line of Credit
Line of Credit Facility [Line Items]
Increase in borrowing capacity	$ 100,000,000.0
Total Facility		500,000,000.0			$ 400,000,000.0
Maximum aggregate letters of credit allowed		200,000,000.0
Increase in maximum aggregate facility subject to certain conditions	$ 100,000,000.0
Maximum aggregate facility, including increase subject to certain conditions		600,000,000.0
Line of Credit | SJI | Revolving Credit Facility
Line of Credit Facility [Line Items]
Term (in years)	5 years
Total Facility		50,000,000
Line of Credit | SJI | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity		50,000,000.0
Line of Credit | SJG
Line of Credit Facility [Line Items]
Total Facility		$ 210,000,000
Weighted average interest rate on borrowings		2.39%	2.42%
Average borrowings outstanding		$ 96,200,000	$ 67,900,000
Debt covenant, ratio of indebtedness to total capitalization		0.65
Line of Credit | SJG | Uncommitted Bank Line
Line of Credit Facility [Line Items]
Total Facility		$ 10,000,000
Line of Credit | ETG/ELK | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility		200,000,000.0
Additional aggregate borrowing capacity		200,000,000.0
Line of Credit | ETG/ELK | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity		20,000,000.0
Line of Credit | ETG Utility Operations | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility		250,000,000.0
Additional aggregate borrowing capacity		175,000,000.0
Increase in maximum aggregate facility subject to certain conditions	$ 50,000,000.0
Line of Credit | ELK Utility Operations | Revolving Credit Facility
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity		25,000,000.0
Unsecured Debt | South Jersey Gas Commercial Paper Program
Line of Credit Facility [Line Items]
Total Facility		$ 200,000,000.0
Fixed maturities of notes, at maximum number of days		270 days