LINES OF CREDIT - Schedule of Lines of Credit (Details) - USD ($)	Sep. 30, 2019	May 31, 2019
Line of Credit
Line of Credit Facility [Line Items]
Total Facility	$ 1,060,000,000
Usage	823,700,000
Available Liquidity	236,300,000
SJI | Line of Credit
Line of Credit Facility [Line Items]
Total Facility	650,000,000
Usage	502,400,000
Available Liquidity	147,600,000
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 | Line of Credit
Line of Credit Facility [Line Items]
Total Facility	500,000,000.0	$ 400,000,000.0
Usage	352,400,000
Available Liquidity	147,600,000
Letters of credit outstanding	9,600,000
SJG | Line of Credit
Line of Credit Facility [Line Items]
Total Facility	210,000,000
Usage	176,000,000
Available Liquidity	34,000,000
SJG | Line of Credit | Uncommitted Bank Line
Line of Credit Facility [Line Items]
Total Facility	10,000,000
Usage	0
Available Liquidity	10,000,000
SJG | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	800,000
SJG | Commercial Paper and Letters of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	200,000,000
Usage	176,000,000
Available Liquidity	24,000,000
ETG/ELK | Line of Credit | Revolving Credit Facility
Line of Credit Facility [Line Items]
Total Facility	200,000,000.0
Usage	145,300,000
Available Liquidity	54,700,000
ETG/ELK | Line of Credit | Line of Credit
Line of Credit Facility [Line Items]
Letters of credit outstanding	$ 1,000,000.0