| Document and Entity Information Document | Aug. 20, 2021 |
| Cover [Abstract] | |
| Entity Central Index Key | 0000705432 |
| Document Type | 8-K |
| Document Period End Date | Aug. 20, 2021 |
| Entity Registrant Name | Southside Bancshares, Inc. |
| Entity Emerging Growth Company | false |
| Entity Incorporation, State or Country Code | TX |
| Entity File Number | 000-12247 |
| Entity Tax Identification Number | 75-1848732 |
| Entity Address, Address Line One | 1201 S. Beckham Avenue, |
| Entity Address, City or Town | Tyler, |
| Entity Address, State or Province | TX |
| Entity Address, Postal Zip Code | 75701 |
| City Area Code | 903 |
| Local Phone Number | 531-7111 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Title of 12(b) Security | Common stock, $1.25 par value |
| Trading Symbol | SBSI |
| Security Exchange Name | NASDAQ |
| Amendment Flag | false |
