Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2018	May 01, 2018
Document Information [Line Items]
Entity Registrant Name	SOUTH JERSEY INDUSTRIES INC
Entity Central Index Key	0000091928
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding		85,502,759
South Jersey Gas Company
Document Information [Line Items]
Entity Registrant Name	SOUTH JERSEY GAS Co
Entity Central Index Key	0001035216
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		2,339,139