Summary of Significant Accounting and Reporting Policies (Policies)	6 Months Ended
	Jun. 30, 2023
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Presentation	Basis of Presentation In this report, the words “the Company,” “we,” “us,” and “our” refer to the combined entities of Southside Bancshares, Inc. and its subsidiaries, including Southside Bank. The words “Southside” and “Southside Bancshares” refer to Southside Bancshares, Inc. The words “Southside Bank” and “the Bank” refer to Southside Bank. The accompanying unaudited consolidated financial statements have been prepared in accordance with U.S. GAAP for interim financial information and with the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, not all information required by GAAP for complete financial statements is included in these interim statements. In the opinion of management, all adjustments necessary for a fair presentation of such financial statements have been included. Such adjustments consisted only of normal recurring items. The preparation of these consolidated financial statements in accordance with GAAP requires the use of management’s estimates. These estimates are subjective in nature and involve matters of judgment. Actual amounts could differ from these estimates. Interim results are not necessarily indicative of results for a full year. These financial statements should be read in conjunction with the financial statements and notes thereto in our Annual Report on Form 10-K for the year ended December 31, 2022.
Reclassifications	Certain prior period amounts may be reclassified to conform to current year presentation. Current Expected Credit Losses - Troubled Debt Restructurings and Vintage Disclosures We adopted ASU 2022-02, “Financial Instruments - Credit Losses (Topic 326): Troubled Debt Restructurings and Vintage Disclosures” on January 1, 2023, the effective date of the guidance, on a prospective basis. ASU 2022-02 eliminated the accounting guidance for TDRs, while enhancing disclosure requirements for certain loan refinancings and restructurings by creditors when a borrower is experiencing financial difficulty. Specifically, rather than applying the recognition and measurement guidance for TDRs, an entity must apply the loan refinancing and restructuring guidance to determine whether a modification results in a new loan or a continuation of an existing loan. Additionally, ASU 2022-02 requires an entity to disclose current-period gross write-offs by year of origination for financing receivables within the scope of Subtopic 326-20, “Financial Instruments—Credit Losses—Measured at Amortized Cost.” ASU 2022-02 did not have a material impact on our consolidated financial statements.
Accounting Changes and Reclassifications and Accounting Pronouncements	Accounting Pronouncements In March 2020, the FASB issued ASU 2020-04, “Reference Rate Reform (Topic 848): Facilitation of the Effects of Reference Rate Reform on Financial Reporting.” ASU 2020-04 is intended to provide relief for companies preparing for discontinuation of interest rates based on LIBOR. The ASU provides optional expedients and exceptions for applying GAAP to contract modifications and hedging relationships, subject to meeting certain criteria, that reference LIBOR or other reference rates expected to be discontinued. ASU 2020-04 also provides for a one-time sale and/or transfer to AFS or trading to be made for HTM debt securities that both reference an eligible reference rate and were classified as HTM before January 1, 2020. ASU 2020-04 was effective for all entities as of March 12, 2020 and through December 31, 2022. Companies can apply the ASU as of the beginning of the interim period that includes March 12, 2020 or any date thereafter. The guidance requires companies to apply the guidance prospectively to contract modifications and hedging relationships while the one-time election to sell and/or transfer debt securities classified as HTM may be made any time after March 12, 2020. Additionally, in January 2021, the FASB issued ASU 2021-01, “Reference Rate Reform (Topic 848): Scope,” which provided additional clarification that certain optional expedients and exceptions noted above apply to derivative instruments that use an interest rate for margining, discounting or contract price alignment that is modified as a result of reference rate reform. In December 2022, the FASB issued ASU 2022-06, “Reference Rate Reform (Topic 848): Deferral of the Sunset Date of Topic 848,” which was effective upon issuance and deferred the sunset date in Topic 848 from December 31, 2022 to December 31, 2024. We established an officer level committee to guide our transition from LIBOR in October 2019 and are transitioning to alternative rates consistent with industry timelines. We continue to evaluate our LIBOR exposure. Our trust preferred subordinated debentures will transition to an adjusted SOFR index in accordance with the Federal Reserve final rule implementing the Adjustable Interest Rate Act. Our cash flow hedges will transition to an adjusted SOFR index in accordance with the ISDA 2020 IBOR Fallbacks Protocol. We have identified our products that utilize LIBOR and have implemented enhanced fallback language to facilitate the transition to alternative reference rates. We have evaluated our systems and are offering alternative rates. We are no longer offering LIBOR indexed rates on newly originated loans. ASU 2020-04 and ASU 2021-01 are not expected to have a material impact on our consolidated financial statements.