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LONG-TERM DEBT - LT Debt Interest Rates (Details) - USD ($) $ in Thousands | Nov. 14, 2025 | Aug. 10, 2007 | Aug. 08, 2007 | May 20, 2005 | Sep. 04, 2003 | Dec. 31, 2023 | Jun. 14, 2023 | Dec. 31, 2022 | Nov. 06, 2020 | Oct. 10, 2007
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Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other long-term debt | [1] |  |  |  |  |  |  | $ 60,270 |  |  | $ 60,265 |  |  |
Southside Statutory Trust III |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other long-term debt |  |  |  |  |  |  | $ 20,619 | 20,578 | [1],[2] |  | 20,573 | [1],[2] |  |
Southside Statutory Trust III | Three-Month Secured Overnight Financing Rate (SOFR) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | [3] |  |  |  |  |  | 3.20% |  |  |  |  |  |  |
Southside Statutory Trust IV |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other long-term debt |  |  |  | $ 23,196 |  |  |  | 23,196 | [1] |  | 23,196 | [1] |  |
Southside Statutory Trust IV | Three-Month Secured Overnight Financing Rate (SOFR) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | [3] |  |  | 1.56% |  |  |  |  |  |  |  |  |  |
Southside Statutory Trust V |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other long-term debt |  |  | $ 12,887 |  |  |  |  | 12,887 | [1] |  | 12,887 | [1] |  |
Southside Statutory Trust V | Three-Month Secured Overnight Financing Rate (SOFR) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | [3] |  | 2.51% |  |  |  |  |  |  |  |  |  |  |
Magnolia Trust Company I |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Other long-term debt |  |  |  |  | $ 3,609 | [4] |  | $ 3,609 | [1] |  | $ 3,609 | [1] |  | $ 3,600
Magnolia Trust Company I | Three-Month Secured Overnight Financing Rate (SOFR) |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate | [3],[4] |  |  |  | 2.06% |  |  |  |  |  |  |  |  |
3.875% Subordinated Notes |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt face amount | [5] |  |  |  |  |  |  |  |  |  |  |  | $ 100,000 |
Stated interest rate |  |  |  |  |  |  |  |  |  |  |  |  | 3.875% |
Debt Instrument, Repurchase Amount |  |  |  |  |  |  |  |  |  | $ 5,000 |  |  |  |
Forecast [Member] | 3.875% Subordinated Notes | Secured Overnight Financing Rate (SOFR) Overnight Index Swap Rate |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |
Basis spread on variable rate |  | 3.66% |  |  |  |  |  |  |  |  |  |  |  |
[1] | This debt consists of trust preferred securities that qualify under the risk-based capital guidelines as Tier 1 capital, subject to certain limitations.
[2] | The unamortized debt issuance costs reflected in the carrying amount of the Southside Statutory Trust III junior subordinated debentures totaled $41,000 at December 31, 2023 and $46,000 at December 31, 2022.
[3] | Effective July 1, 2023, the Comany began utilizing SOFR to reset rates on our floating rate trust preferred debentures, due to the fact that LIBOR ceased to be published as of June 30, 2023.
[4] | On October 10, 2007, as part of an acquisition we assumed $3.6 million of floating rate junior subordinated debentures issued in 2005 to Magnolia Trust Company I.
[5] | On June 14, 2023, the Company repurchased $5.0 million of the $100.0 million fixed-to-floating rate subordinated notes that mature on November 15, 2030.

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