FINANCIAL INSTRUMENTS (Details)	3 Months Ended			12 Months Ended
	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2017 USD ($) counterparty	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2011
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restricted Investments				$ 31,876,000	$ 13,628,000
Equity investment impairments				0		$ 0
Investment in Affiliate				62,292,000	28,906,000
Notes Receivable				$ (22,884,000)	(9,916,000)	9,916,000
Number of counterparties | counterparty				1
Carrying amount of long-term debt, including current maturities				$ 1,204,173,000	1,047,482,000
Unamortized debt issuance costs				17,400,000	7,600,000
Derivatives-Energy Related Assets | Supplier concentration risk
Accounts, Notes, Loans and Financing Receivable [Line Items]
Current and noncurrent derivatives				$ 6,500,000
Percentage of current and noncurrent derivatives				13.50%
Energenic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equity interest							50.00%
Contract term							20 years
Equity investment impairments			$ 7,700,000			7,700,000
Share of settlement					7,500,000
Associated costs					7,000,000
Notes receivable due from Affiliate				$ 13,600,000
Energenic | Other Income
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds received		$ 2,100,000
Energenic | Equity in Earnings of Affiliated Companies
Accounts, Notes, Loans and Financing Receivable [Line Items]
Proceeds received	$ 5,300,000
Marina | Energenic
Accounts, Notes, Loans and Financing Receivable [Line Items]
Equity interest				50.00%
South Jersey Gas Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Margin accounts with selected counterparties to support risk management activities					3,600,000
Restricted Investments				$ 2,912,000	32,000
Notes Receivable				0	(9,916,000)	$ 9,916,000
Carrying amount of long-term debt, including current maturities				829,173,000	645,082,000
Unamortized debt issuance costs				$ 7,300,000	6,000,000
South Jersey Gas Company | Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of loans				5 years
South Jersey Gas Company | Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Term of loans				10 years
South Jersey Gas Company | Unnamed Counterparty
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restricted Investments				$ 2,900,000
Level 1
Accounts, Notes, Loans and Financing Receivable [Line Items]
Margin accounts with selected counterparties to support risk management activities				31,600,000	11,700,000
Level 1 | Marina
Accounts, Notes, Loans and Financing Receivable [Line Items]
Restricted investments held in escrow				300,000	1,900,000
Level 2
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of long-term debt, including current maturities				1,216,100,000	1,080,800,000
Carrying amount of long-term debt, including current maturities				1,186,800,000	1,039,900,000
Level 2 | South Jersey Gas Company
Accounts, Notes, Loans and Financing Receivable [Line Items]
Fair value of long-term debt, including current maturities				838,500,000	673,100,000
Carrying amount of long-term debt, including current maturities				821,900,000	639,100,000
Level 2 | South Jersey Gas Company | Financing receivable
Accounts, Notes, Loans and Financing Receivable [Line Items]
Long-term receivables, net of unamortized discount				7,000,000	9,500,000
Imputed interest on long term receivables				$ (700,000)	$ (900,000)