Entity tax identification number Entity Tax Identification Number Rollovers EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Rollover Maximum Maximum [Member] 2 EBP, Vested Percentage, Service Period, Two Years EBP, Vested Percentage, Service Period, Two Years Forfeited nonvested account, decrease from administrative expense EBP, Forfeited Nonvested Account, Decrease from Administrative Expense Legal Entity [Axis] Legal Entity [Axis] Note receivable from participant, new loan reduction, highest loan balance period EBP, Note Receivable From Participant, New Loan Reduction, Highest Loan Balance Period EBP, Note Receivable From Participant, New Loan Reduction, Highest Loan Balance Period Statistical Measurement [Domain] Statistical Measurement [Domain] EBP, Description of Plan [Table] EBP, Description of Plan [Table] Mutual Funds Mutual Fund [Member] Requisite service period for discretionary matching contribution eligibility (in hours) EBP, Requisite Service Period, Discretionary Matching Contribution Eligibility EBP, Requisite Service Period, Discretionary Matching Contribution Eligibility EBP, Related Party and Party-in-Interest Transactions [Table] EBP, Related Party and Party-in-Interest Transactions [Table] Total deductions EBP, Change in Net Asset Available for Benefit, Decrease Note receivable from participant, account, maximum borrowing, amount EBP, Note Receivable from Participant, Account, Maximum Borrowing, Amount FAIR VALUE MEASUREMENTS EBP, Investment, Fair Value and NAV [Text Block] Note receivable from participant, account, minimum borrowing, amount EBP, Note Receivable from Participant, Account, Minimum Borrowing, Amount Contributions Tranche Two Contributions Tranche Two [Member] Contributions Tranche Two Investments, at fair value EBP, Investment, Excluding Plan Interest in Master Trust, Fair Value Contributions Tranche [Domain] Contributions Tranche [Domain] Contributions Tranche [Domain] Less than 2 EBP, Vested Percentage, Service Period, Less Than Two Years EBP, Vested Percentage, Service Period, Less Than Two Years Level 1 Fair Value, Inputs, Level 1 [Member] EBP, Reconciliation of Financial Statement to Form 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Table Text Block] EBP, Investment, Fair Value and NAV [Abstract] Statistical Measurement [Axis] Statistical Measurement [Axis] Schedule of Vesting by Periods of Service EBP, Schedule Of Vesting By Periods Of Service [Table Text Block] EBP, Schedule Of Vesting By Periods Of Service ADDITIONS: EBP, Change in Net Asset Available for Benefit, Increase [Abstract] EBP, Statement of Change in Net Asset Available for Benefit [Table] EBP, Statement of Change in Net Asset Available for Benefit [Table] Payment of Benefits EBP, Payment to Participant [Policy Text Block] Amendment Flag Amendment Flag Basis of Accounting EBP, Basis of Accounting [Policy Text Block] EBP, Schedule of Asset Held for Investment [Table] EBP, Schedule of Asset Held for Investment [Table] Prior year employer match receivable EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Decrease, Prior Year Employer Match Receivable EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Decrease, Prior Year Employer Match Receivable Investment, number of shares (in shares) EBP, Investment, Number of Shares EBP, Description of Plan and Accounting Change [Abstract] Receivables: EBP, Receivable [Abstract] Schedule of Fair Value EBP, Investment, Fair Value and NAV [Table Text Block] 4 EBP, Vested Percentage, Service Period, Four Years EBP, Vested Percentage, Service Period, Four Years Investments [Domain] Investments [Domain] Contributions Tranche One Contributions Tranche One [Member] Contributions Tranche One Use of Estimates EBP, Use of Estimate [Policy Text Block] Pooled Separate Accounts EBP, Pooled Separate Account [Member] Schedule H, Line 4i – Schedule of Assets (Held At End of Year) EBP, Schedule of Asset Held for Investment [Text Block] Cover [Abstract] RISK AND UNCERTAINTIES EBP, Risk and Uncertainty [Text Block] Employer EBP, Change in Net Asset Available for Benefit, Increase from Employer Contribution, Cash Minimum Minimum [Member] Investment Type [Axis] Investment Type [Axis] Interest income on notes receivable from participants EBP, Change in Net Asset Available for Benefit, Increase from Interest Income on Note Receivable from Participant Total contributions EBP, Change in Net Asset Available for Benefit, Increase from Contribution Participant EBP, Change in Net Asset Available for Benefit, Increase from Participant Contribution, Excluding Rollover Investments, employer-level liquidation or employer initiated transfer of plan's interest, surrender charge percentage EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Surrender Charge Percentage EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Surrender Charge Percentage Net appreciation in fair value of investments EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Gain (Loss) on Investment Dividend and interest income EBP, Change in Net Asset Available for Benefit, Increase from Interest and Dividend Income on Investment EBP, Description of Plan [Line Items] EBP, Description of Plan [Line Items] Plan number EBP, Plan Number EBP, Investment, Fair Value and NAV [Line Items] EBP, Investment, Fair Value and NAV [Line Items] DESCRIPTION OF PLAN EBP, Description of Plan [Text Block] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Change in Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Table] EBP, Statement of Net Asset Available for Benefit [Table] Investments, employer-level liquidation or employer initiated transfer of plan's interest, advance notice period EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Advance Notice Period EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Advance Notice Period EBP, Schedule of Asset Held for Investment [Line Items] EBP, Schedule of Asset Held for Investment [Line Items] 6 or more EBP, Vested Percentage, Service Period, Six Years And Thereafter EBP, Vested Percentage, Service Period, Six Years And Thereafter Southside Bancshares, Inc. Common Stock EBP, Employer, Common Stock [Member] EBP, Schedule of Asset Held for Investment [Abstract] EBP, Accounting Policy [Table] EBP, Accounting Policy [Table] Total additions EBP, Change in Net Asset Available for Benefit, Increase EBP, Note Receivable from Participant, Allowance for Credit Loss EBP, Note Receivable from Participant, Allowance for Credit Loss Investment income: EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment [Abstract] Investment, Identifier [Axis] Investment, Identifier [Axis] Administrative expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Total EBP, Asset Held for Investment Document Information [Line Items] Document Information [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Line Items] EBP, Risk and Uncertainty [Table] EBP, Risk and Uncertainty [Table] Employer contribution, participant compensation matched, percentage EBP, Employer Contribution, Participant Compensation Matched, Percentage EBP, Statement of Change in Net Asset Available for Benefit [Abstract] Level 2 Fair Value, Inputs, Level 2 [Member] Participant contribution, automatic, annual increase deferral rate EBP, Participant Contribution, Automatic, Annual Increase Deferral Rate EBP, Participant Contribution, Automatic, Annual Increase Deferral Rate Net income per the Form 5500 EBP, Form 5500 Caption, Net Income (Loss) EBP, Tax Status [Table] EBP, Tax Status [Table] Net increase Net increase in the net assets available for benefits EBP, Change in Net Asset Available for Benefit, Increase (Decrease) RELATED-PARTY TRANSACTIONS EBP, Related Party and Party-in-Interest Transactions [Text Block] Investments, employer-level liquidation or employer initiated transfer of plan's interest, participant transfers cumulative percentage EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Participant Transfers Cumulative Percentage EBP, Investments, Employer-Level Liquidation Or Employer Initiated Transfer Of Plan's Interest, Participant Transfers Cumulative Percentage Participant investment, maximum employer stock percentage EBP, Participant Investment, Maximum Employer Stock Percentage EBP, Participant Investment, Maximum Employer Stock Percentage EBP, Related Party and Party-in-Interest Transactions [Abstract] EBP, Accounting Policy, Accounting Standard Update, and Change in Accounting Principle [Abstract] Participant contribution, automatic, deferral rate EBP, Participant Contribution, Automatic, Deferral Rate Investments: EBP, Investment, Fair Value [Abstract] Benefits paid to participants EBP, Change in Net Asset Available for Benefit, Decrease from Payment to Participant Current Value EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] 3 EBP, Vested Percentage, Service Period, Three Years EBP, Vested Percentage, Service Period, Three Years ASSETS Assets [Abstract] EBP, Statement of Net Asset Available for Benefit [Abstract] Current year employer match receivable EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase, Current Year Employer Match Receivable EBP, Reconciliation to Form 5500, Change in Net Asset Available for Benefit, Increase, Current Year Employer Match Receivable EBP, Accounting Policy [Line Items] EBP, Accounting Policy [Line Items] EBP, Tax Status [Abstract] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] EBP, Reconciliation of Financial Statement to Form 5500 [Line Items] RECONCILIATION OF FINANCIAL STATEMENTS TO FORM 5500 EBP, Reconciliation of Financial Statement to Form 5500 [Text Block] Participant loans EBP, Asset Held for Investment, Participant Loan, after Deemed Distribution Investment Valuation and Income Recognition EBP, Investment [Policy Text Block] Document Type Document Type EBP 002 EBP 002 [Member] EBP 002 Entity Central Index Key Entity Central Index Key Asset held for investment, participant loan, interest rate EBP, Asset Held for Investment, Participant Loan, Interest Rate EBP, Reconciliation of Financial Statement to Form 5500 [Abstract] Collective Investment Trusts Common Collective Trust [Member] NET ASSETS AVAILABLE FOR BENEFITS: EBP, Net Asset Available for Benefit [Abstract] EBP, Risk and Uncertainty [Abstract] EBP, Tax Status [Line Items] EBP, Tax Status [Line Items] DEDUCTIONS: EBP, Change in Net Asset Available for Benefit, Decrease [Abstract] Forfeited nonvested account, decrease from employer contribution EBP, Forfeited Nonvested Account, Decrease from Employer Contribution Employer contribution maximum vesting age EBP, Employer Contribution Maximum Vesting Age EBP, Employer Contribution Maximum Vesting Age Notes receivable from participants EBP, Note Receivable from Participant Note receivable from participant, number of maximum loans at any point in time EBP, Note Receivable From Participant, Number Of Maximum Loans At Any Point In Time EBP, Note Receivable From Participant, Number Of Maximum Loans At Any Point In Time Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] SIGNIFICANT ACCOUNTING POLICIES EBP, Summary of Accounting Policy [Text Block] Entity Registrant Name Entity Registrant Name Employer contribution vesting percentage EBP, Employer Contribution Vesting Percentage EBP, Employer Contribution Vesting Percentage TAX STATUS EBP, Tax Status [Text Block] 5 EBP, Vested Percentage, Service Period, Five Years EBP, Vested Percentage, Service Period, Five Years Note receivable from participant, account, maximum borrowing, to total account, percentage EBP, Note Receivable from Participant, Account, Maximum Borrowing, to Total Account, Percentage Employer match receivable EBP, Form 5500 Caption, Receivables, Employer Contributions Document Information [Table] Document Information [Table] Contributions Tranche [Axis] Contributions Tranche [Axis] Contributions Tranche Notes Receivable from Participants EBP, Note Receivable from Participant [Policy Text Block] Total investment income EBP, Change in Net Asset Available for Benefit, Increase (Decrease) from Income (Loss) on Investment EBP, Related Party and Party-in-Interest Transactions [Line Items] EBP, Related Party and Party-in-Interest Transactions [Line Items] Level 3 Fair Value, Inputs, Level 3 [Member] Benefit payments, mandatory distribution upon separation, vested account balance EBP, Benefit Payments, Mandatory Distribution Upon Separation, Vested Account Balance EBP, Benefit Payments, Mandatory Distribution Upon Separation, Vested Account Balance Net assets available for benefits Beginning of year End of year Net assets available for benefits - financial statements EBP, Net Asset Available for Benefit Total investments EBP, Investment, Excluding Plan Interest in Master Trust, Fair and Contract Value Entity [Domain] Entity [Domain] Contributions: EBP, Change in Net Asset Available for Benefit, Increase from Contribution [Abstract] Requisite service period EBP, Requisite Service Period EBP, Requisite Service Period Fully benefit responsive investment, at contract value EBP, Investment, Excluding Plan Interest in Master Trust, Contract Value Forfeited nonvested account EBP, Forfeited Nonvested Account Employer contribution, matching percentage EBP, Employer Contribution, Matching Percentage Note receivable from participant, maximum borrowing term EBP, Note Receivable From Participant, Maximum Borrowing Term EBP, Note Receivable From Participant, Maximum Borrowing Term Net assets available for benefits - Form 5500 EBP, Form 5500 Caption, Net Assets EBP, Investment, Fair Value and NAV [Table] EBP, Investment, Fair Value and NAV [Table] EBP, Statement of Net Asset Available for Benefit [Line Items] EBP, Statement of Net Asset Available for Benefit [Line Items]