LONG-TERM DEBT (Details) - USD ($)	1 Months Ended			12 Months Ended
	Aug. 31, 2016	Jul. 31, 2016	Jan. 31, 2016	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				$ 645,082,000	$ 611,991,000
Less Current Maturities				(215,909,000)	(27,909,000)
Long-Term Debt (L)				429,173,000	584,082,000
Long-term Debt, Fiscal Year Maturity [Abstract]
2017				215,909,000
2018				38,909,000
2019				18,909,000
2020				17,909,000
2021				27,909,000
Letter of credit provided				210,000,000
Debt issuance costs				$ 6,000,000	6,600,000
First Mortgage Bonds | Series Due 2016, 5.437%
Debt Instrument [Line Items]
Stated interest rate	5.437%			5.437%
Total Long-Term Debt Outstanding (L)				$ 0	10,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Retired debt	$ 10,000,000
First Mortgage Bonds | Series Due 2016, 4.60%
Debt Instrument [Line Items]
Stated interest rate				4.60%
Total Long-Term Debt Outstanding (L)				$ 0	17,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Retired debt		$ 17,000,000
First Mortgage Bonds | Series Due 2017, 4.657%
Debt Instrument [Line Items]
Stated interest rate				4.657%
Total Long-Term Debt Outstanding (L)				$ 15,000,000	15,000,000
First Mortgage Bonds | Series Due 2018, 7.97%
Debt Instrument [Line Items]
Stated interest rate				7.97%
Total Long-Term Debt Outstanding (L)				$ 10,000,000	10,000,000
First Mortgage Bonds | Series Due 2018, 7.125%
Debt Instrument [Line Items]
Stated interest rate				7.125%
Total Long-Term Debt Outstanding (L)				$ 20,000,000	20,000,000
First Mortgage Bonds | Series Due 2019, 5.587%
Debt Instrument [Line Items]
Stated interest rate				5.587%
Total Long-Term Debt Outstanding (L)				$ 10,000,000	10,000,000
First Mortgage Bonds | Series Due 2024, 3.00%
Debt Instrument [Line Items]
Stated interest rate				3.00%
Total Long-Term Debt Outstanding (L)				$ 50,000,000	50,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Annual payments due				$ 10,000,000
First Mortgage Bonds | Series Due 2024, 3.03%
Debt Instrument [Line Items]
Stated interest rate				3.03%
Total Long-Term Debt Outstanding (L)				$ 35,000,000	35,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Annual payments due				$ 7,000,000
First Mortgage Bonds | Series Due 2025, 3.63%
Debt Instrument [Line Items]
Stated interest rate				3.63%
Total Long-Term Debt Outstanding (L)				$ 8,182,000	9,091,000
First Mortgage Bonds | Series Due 2025, 3.63% | South Jersey Gas Company
Debt Instrument [Line Items]
Stated interest rate				3.63%
Less Current Maturities				$ (900,000)
Long-term Debt, Fiscal Year Maturity [Abstract]
Payment towards the principal				$ 900,000
First Mortgage Bonds | Series Due 2026, 4.84%
Debt Instrument [Line Items]
Stated interest rate				4.84%
Total Long-Term Debt Outstanding (L)				$ 15,000,000	15,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Annual payments due				$ 2,500,000
First Mortgage Bonds | Series Due 2026, 4.93%
Debt Instrument [Line Items]
Stated interest rate				4.93%
Total Long-Term Debt Outstanding (L)				$ 45,000,000	45,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Annual payments due				$ 7,500,000
First Mortgage Bonds | Series Due 2027, 4.03%
Debt Instrument [Line Items]
Stated interest rate				4.03%
Total Long-Term Debt Outstanding (L)				$ 45,000,000	45,000,000
First Mortgage Bonds | Series Due 2030, 4.01%
Debt Instrument [Line Items]
Stated interest rate				4.01%
Total Long-Term Debt Outstanding (L)				$ 50,000,000	50,000,000
First Mortgage Bonds | Series Due 2030, 4.01% | South Jersey Gas Company
Debt Instrument [Line Items]
Stated interest rate				4.01%
Total Long-Term Debt Outstanding (L)				$ 50,000,000
First Mortgage Bonds | Series Due 2030, 4.23%
Debt Instrument [Line Items]
Stated interest rate				4.23%
Total Long-Term Debt Outstanding (L)				$ 30,000,000	30,000,000
First Mortgage Bonds | Series Due 2032, 3.74%
Debt Instrument [Line Items]
Stated interest rate				3.74%
Total Long-Term Debt Outstanding (L)				$ 35,000,000	35,000,000
First Mortgage Bonds | Series Due 2033, 5.55%
Debt Instrument [Line Items]
Stated interest rate				5.55%
Total Long-Term Debt Outstanding (L)				$ 32,000,000	32,000,000
First Mortgage Bonds | Series Due 2034, 6.213%
Debt Instrument [Line Items]
Stated interest rate				6.213%
Total Long-Term Debt Outstanding (L)				$ 10,000,000	10,000,000
First Mortgage Bonds | Series Due 2035, 5.45%
Debt Instrument [Line Items]
Stated interest rate				5.45%
Total Long-Term Debt Outstanding (L)				$ 10,000,000	10,000,000
First Mortgage Bonds | MTN, 4.01%, Due November 2018 and November 2019 | South Jersey Gas Company
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				8,000,000
First Mortgage Bonds | MTN, 4.01%, Due November 2025 | South Jersey Gas Company
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				2,000,000
First Mortgage Bonds | MTN, 4.01%, Due November 2026 | South Jersey Gas Company
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				3,000,000
First Mortgage Bonds | MTN, 4.01%, Due November 2027 | South Jersey Gas Company
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				8,000,000
First Mortgage Bonds | MTN, 4.01%, Due November 2028, November 2029 and November 2030 | South Jersey Gas Company
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				7,000,000
Bonds at variable rates | Series A 2006 Tax-Exempt First Mortgage Bonds, Variable Rate, due 2036
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				$ 24,900,000	24,900,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Interest rate at end of period				0.74%
Loans Payable | Term Line of Credit
Debt Instrument [Line Items]
Total Long-Term Debt Outstanding (L)				$ 200,000,000	139,000,000
Long-term Debt, Fiscal Year Maturity [Abstract]
Letter of credit provided				200,000,000.0
Outstanding debt				$ 200,000,000	$ 139,000,000
Average interest rate			1.41%		1.17%
Additional issuance of long-term debt			$ 61,000,000
Medium-term Notes
Long-term Debt, Fiscal Year Maturity [Abstract]
Approved borrowing capacity					$ 400,000,000.0