| Cover | Feb. 24, 2021 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 24, 2021 |
| Entity Incorporation, State or Country Code | NJ |
| Entity File Number | 1-6364 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0000091928 |
| Amendment Flag | false |
| Entity Registrant Name | SOUTH JERSEY INDUSTRIES, INC. |
| Common Stock [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Common Stock |
| Trading Symbol | SJI |
| Security Exchange Name | NYSE |
| Convertible Notes Payable [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | 5.625% Junior Subordinated Notes due 2079 |
| Trading Symbol | SJIJ |
| Security Exchange Name | NYSE |
| Capital Units [Member] | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Corporate Units |
| Trading Symbol | SJIU |
| Security Exchange Name | NYSE |
