| Document and Entity Information | Jul. 28, 2021 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 28, 2021 |
| Entity Registrant Name | SOUTH JERSEY GAS COMPANY |
| Entity Incorporation, State or Country Code | NJ |
| Entity File Number | 000-22211 |
| 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 |
| 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 | 0001035216 |
