LINES OF CREDIT (Details)		1 Months Ended	12 Months Ended
	Jun. 26, 2018 USD ($) Covenant	Jun. 30, 2019 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Sep. 23, 2019 USD ($)	May 31, 2019 USD ($)	Dec. 31, 2017
Line of Credit Facility [Line Items]
Maximum amounts outstanding			$ 907,500,000	$ 497,000,000.0
Unsecured debt
Line of Credit Facility [Line Items]
Principal amount issued					$ 100,000,000.0
Line of Credit
Line of Credit Facility [Line Items]
Total Facility			1,060,000,000
Usage			860,000,000
Available Liquidity			$ 200,000,000
Financial covenant, ratio of indebtedness to total capitalization, syndicate maximum			0.70
Weighted average interest rate on borrowings			2.67%	3.32%			2.46%
Average borrowings outstanding			$ 560,200,000	$ 265,500,000
Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Maximum aggregate letters of credit allowed	$ 50,000,000.0
Unsecured debt | South Jersey Gas commercial paper program
Line of Credit Facility [Line Items]
Total Facility			$ 200,000,000.0
Fixed maturities of notes, which may not exceed specified number of days			270 days
SJI | Unsecured debt
Line of Credit Facility [Line Items]
Principal amount issued			$ 100,000,000
SJI | Line of Credit
Line of Credit Facility [Line Items]
Total Facility			650,000,000
Usage			582,600,000
Available Liquidity			67,400,000
SJI | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Total Facility		$ 500,000,000.0	500,000,000			$ 400,000,000.0
Usage			432,600,000
Available Liquidity			67,400,000
Letters of credit outstanding			9,500,000
Increase in borrowing capacity		100,000,000.0
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
SJI | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility			50,000,000
Usage			50,000,000
Available Liquidity			0
SJI | Line of Credit | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity		$ 50,000,000.0
South Jersey Gas Company
Line of Credit Facility [Line Items]
Maximum amounts outstanding			196,500,000	$ 177,000,000.0
South Jersey Gas Company | Line of Credit
Line of Credit Facility [Line Items]
Total Facility			210,000,000
Usage			172,100,000
Available Liquidity			$ 37,900,000
Weighted average interest rate on borrowings			1.99%	2.96%			1.88%
Average borrowings outstanding			$ 113,300,000	$ 86,000,000.0
Financial covenant, ratio of indebtedness to consolidated total capitalization (not more than)			0.65
South Jersey Gas Company | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding			$ 800,000
South Jersey Gas Company | Line of Credit | Uncommitted Bank Lines
Line of Credit Facility [Line Items]
Total Facility			10,000,000
Usage			0
Available Liquidity			10,000,000
South Jersey Gas Company | Commercial paper and letters of credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility			200,000,000
Usage			172,100,000
Available Liquidity			27,900,000
Elizabethtown Gas and Elkton Gas | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding			1,000,000.0
Elizabethtown Gas and Elkton Gas | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	200,000,000.0		200,000,000
Usage			105,300,000
Available Liquidity			$ 94,700,000
Additional aggregate borrowing capacity	$ 200,000,000.0
Term of agreement (in years)	2 years
Number of financial covenants | Covenant	1
Elizabethtown Gas and Elkton Gas | Line of Credit | Swingline Loan
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity	$ 20,000,000.0
ETG Utility Operations | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	250,000,000.0
Additional aggregate borrowing capacity	190,000,000.0
Increase in maximum aggregate facility subject to certain conditions	50,000,000.0
ELK Utility Operations | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Additional aggregate borrowing capacity	$ 10,000,000.0