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DISCONTINUED OPERATIONS AND AFFILIATIONS 2 (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2015
Mar. 31, 2014
Dec. 31, 2014
Affiliations [Abstract]      
Investments in unconsolidated affiliates $ 1.7sji_NetAdvancestoUnconsolidatedAffiliates $ 2.9sji_NetAdvancestoUnconsolidatedAffiliates  
Notes Receivable - affiliate 52.4sji_NotesReceivableRelatedPartiesCurrentNoncurrent   51.5sji_NotesReceivableRelatedPartiesCurrentNoncurrent
Due from Affiliate, Noncurrent, Secured By Property, Plant, And Equipment 39.4sji_DuefromAffiliateNoncurrentSecuredByPropertyPlantAndEquipment    
Interest accrual on secured notes receivable (in hundredths) 7.50%us-gaap_DebtInstrumentInterestRateStatedPercentage    
Due from Affiliate, Noncurrent, Unsecured 13.0sji_DuefromAffiliateNoncurrentUnsecured    
Net asset - included in investment in affiliates and other noncurrent liabilities 66.9sji_InvestmentInAffiliateNetOfGuarantees    
Combined equity contributions and the notes receivable - affiliate $ 120.2sji_MaximumExposureToLossOnAffiliates    
Energenic US LLC      
Affiliations [Abstract]      
Equity interest (in hundredths) 50.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= sji_EnergenicUsLlcMember
   
Potato Creek, LLC (Potato Creek)      
Affiliations [Abstract]      
Equity interest (in hundredths) 30.00%us-gaap_EquityMethodInvestmentOwnershipPercentage
/ us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis
= sji_PotatoCreekLlcPotatoCreekMember