Cover page - shares	3 Months Ended
	Mar. 31, 2021	May 01, 2021
Document Information [Line Items]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
Document Transition Report	false
Entity File Number	1-6364
Entity Registrant Name	South Jersey Industries, Inc.
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	22-1901645
Entity Address, Address Line One	1 South Jersey Plaza
Entity Address, City or Town	Folsom
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08037
City Area Code	(609)
Local Phone Number	561-9000
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		112,421,394
Entity Central Index Key	0000091928
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false
Common Stock
Document Information [Line Items]
Title of 12(b) Security	Common Stock - $1.25 par value per share
Trading Symbol	SJI
Security Exchange Name	NYSE
5.625% Junior Subordinated Notes due 2079
Document Information [Line Items]
Title of 12(b) Security	5.625% Junior Subordinated Notes due 2079
Trading Symbol	SJIJ
Security Exchange Name	NYSE
Corporate Units
Document Information [Line Items]
Title of 12(b) Security	Corporate Units
Trading Symbol	SJIV
Security Exchange Name	NYSE
SJG
Document Information [Line Items]
Entity File Number	000-22211
Entity Registrant Name	South Jersey Gas Co
Entity Incorporation, State or Country Code	NJ
Entity Tax Identification Number	21-0398330
Entity Address, Address Line One	1 South Jersey Plaza
Entity Address, City or Town	Folsom
Entity Address, State or Province	NJ
Entity Address, Postal Zip Code	08037
City Area Code	(609)
Local Phone Number	561-9000
Entity Filer Category	Non-accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		2,339,139
Entity Central Index Key	0001035216
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q1
Amendment Flag	false