Receivables [Abstract] Schedule of Financing Receivables Past Due [Table] Schedule of Financing Receivables Past Due [Table] Class of Financing Receivable [Axis] Class of Financing Receivable, Type [Axis] Class of Financing Receivable [Domain] Class of Financing Receivable, Type [Domain] Construction Real Estate Loans Construction Loans [Member] 1-4 Family Residential Real Estate Loans Residential Real Estate [Member] Commercial Real Estate Loans Commercial Real Estate Portfolio Segment [Member] Commercial Loans Commercial Loan [Member] Loans to Individuals Consumer Loan [Member] Financing Receivable, Recorded Investment, Past Due [Line Items] Financing Receivable, Recorded Investment, Past Due [Line Items] Nonaccrual loans Financing Receivable, Recorded Investment, Nonaccrual Status Debt Disclosure [Abstract] Debt [Table] Debt [Table] Debt [Table] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Federal funds purchased and repurchase agreements: Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member] FHLB borrowings: Federal Home Loan Bank Advances [Member] Subordinated notes, net of unamortized debt issuance costs: Subordinated Debt [Member] Trust preferred subordinated debentures, net of unamortized debt issuance costs: Junior Subordinated Debt [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] 2018 Borrowed Funds Maturities Repayments of Principal in the Next Twelve Months Borrowed Funds Maturities Repayments of Principal in the Next Twelve Months 2019 Borrowed Funds Maturing in Year Two Amount of borrowed funds maturing in year two following the date of the latest balance sheet presented in the financial statements. 2020 Borrowed Funds Maturing in Year Three Amount of borrowed funds maturing in year three following the date of the latest balance sheet presented in the financial statements. 2021 Borrowed Funds Maturing in Year Four Amount of borrowed funds maturing in year four following the date of the latest balance sheet presented in the financial statements. 2022 Borrowed Funds Maturing in Year Five Amount of borrowed funds maturing in year five following the date of the latest balance sheet presented in the financial statements. Thereafter Borrowed Funds Maturing After Year Five Amount of borrowed funds maturities after year five following the date of the latest balance sheet presented in the financial statements. Total Debt and Capital Lease Obligations Schedule of Financing Receivable, Troubled Debt Restructurings [Table] Schedule of Financing Receivable, Troubled Debt Restructurings [Table] Class of Financing Receivable [Domain] Municipal Loans Municipal Loans [Member] Class of financing receivables related to state, city or local governments or the agencies operated by state, city or local governments. Financing Receivable, Modifications [Line Items] Financing Receivable, Modifications [Line Items] Troubled Debt Restructuring [Abstract] Restructuring and Related Activities [Abstract] Extend Amortization Period Loan modification related to extending amortization period The amount of modified outstanding recorded investment related to extending amortization period. Interest Rate Reductions Loan modification related to lowering interest rates The amount of modified outstanding recorded investment related to lowering interest rates. Combination Loan modification extending amortization period, lowering interest rate, and principal forgiveness The amount of the modified outstanding recorded investment related to amortization period, lowering interest rate, and principal forgiveness of loans. Total Modifications Financing Receivable, Modifications, Total Modifications for the Period Financing Receivable, Modifications, Total Modifications for the Period Number of Contracts Financing Receivable, Modifications, Number of Contracts Derivative Instruments and Hedging Activities Disclosure [Abstract] Schedule of derivative instruments in statement of financial position, fair value Schedule of Derivative Instruments in Statement of Financial Position, Fair Value [Table Text Block] Weighted average maturity and interest rates on risk management interest rate swaps Weighted Average Maturity And Interest Rates On Risk Management Interest Rate Swaps [Table Text Block] [Table Text Block] for Weighted average remaining maturity of the notional amount of risk management interest rate swaps and weighted average interest rates. Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Abstract] Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Abstract] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Defined Benefit Plans and Other Postretirement Benefit Plans Disclosures [Table] Retirement Plan Type [Axis] Retirement Plan Type [Axis] Retirement Plan Type [Domain] Retirement Plan Type [Domain] Defined Benefit Pension Plan Pension Plan [Member] Defined Benefit Pension Plan Acquired Other Pension Plan [Member] Restoration Plan Other Pension, Postretirement and Supplemental Plans [Member] Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items] Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items] Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract] Defined Benefit Plan, Amounts Recognized in Other Comprehensive Income (Loss) [Abstract] Recognition of net loss Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), Reclassification Adjustment from AOCI, before Tax Recognition of prior service (credit) cost Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), Reclassification Adjustment from AOCI, before Tax Recognition of loss (gain) due to settlements Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement Net (loss) gain occurring during the year Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss) Arising During Period, before Tax Net prior service (cost) credit occurring during the year Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), before Tax Total adjustment during the year Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, before Tax Deferred tax benefit (expense) Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax Other comprehensive (loss) income, net of tax Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, after Tax Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract] Accumulated Other Comprehensive Income by Component, Changes [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Unrealized Gains (Losses) on Securities Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Unrealized Gains (Losses) on Derivatives Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Parent [Member] Net Prior Service (Cost) Credit Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member] Net Gain (Loss) Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member] Total AOCI Attributable to Parent [Member] Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Attributable to Parent, Net of Tax AOCI Attributable to Parent, Net of Tax [Roll Forward] Beginning balance, net of tax Stockholders' Equity Attributable to Parent Other comprehensive income (loss) before reclassifications Other Comprehensive Income (Loss), before Reclassifications, before Tax Reclassified from accumulated other comprehensive income Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax Income tax (expense) benefit Other Comprehensive Income (Loss), Tax Net current-period other comprehensive (loss) income, net of tax Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Reclassification of certain deferred tax effects Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income Ending balance, net of tax Purchased Credit Impaired [Abstract] Purchased Credit Impaired [Abstract] Purchased Credit Impaired [Abstract] Outstanding principal balance Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Outstanding Balance Carrying amount Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Carrying Amount, Net Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward] Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Movement Schedule [Roll Forward] Balance at beginning of period Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield Additions due to acquisition Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Acquired Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Acquired Reclassifications (to) from nonaccretable discount Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Reclassifications (to) from Nonaccretable Difference Accretion Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Accretable Yield, Accretion Balance at end of period Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Estimated Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Quoted Prices in Active Markets for Identical Assets (Level 1) Fair Value, Inputs, Level 1 [Member] Significant Other Observable Inputs (Level 2) Fair Value, Inputs, Level 2 [Member] Significant Unobservable Inputs (Level 3) Fair Value, Inputs, Level 3 [Member] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Axis] Major Types of Debt and Equity Securities [Domain] Major Types of Debt and Equity Securities [Domain] US Treasury US Treasury Securities [Member] U.S. Government Agency Debentures US Government Agencies Debt Securities [Member] State and Political Subdivisions US States and Political Subdivisions Debt Securities [Member] Other Stocks and Bonds Other Stocks and Bonds [Member] This category includes information about ownership interests or the right to acquire ownership interests in corporations and other legal entities which ownership interest is represented by shares of common or preferred stock (which is neither mandatorily redeemable no redeemable at the option of the holder), convertible securities, stock rights, or stock warrants, and debt instrument issued by corporations, governments and governmental agencies, municipalities, and other institutions. Other Equity Securities Equity Securities [Member] Residential MBS Residential Mortgage Backed Securities [Member] Commercial MBS Commercial Mortgage Backed Securities [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest Rate Swaps Interest Rate Swap [Member] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Foreclosed assets Foreclosed Assets [Member] Foreclosed Assets [Member] Impaired loans Receivable, Impaired [Member] Receivable, Impaired [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Total asset recurring fair value measurements Assets, Fair Value Disclosure, Recurring Total liability recurring fair value measurements Liabilities, Fair Value Disclosure, Recurring Total asset nonrecurring fair value measurements Assets, Fair Value Disclosure, Nonrecurring Statement of Stockholders' Equity [Abstract] Issuance of common stock for dividend reinvestment plan (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Net issuance of common stock (in shares) Stock Issued During Period, Shares, New Issues Dividends paid on common stock (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Purchase of common stock (in shares) Treasury Stock, Shares, Acquired Net issuance of common stock under employee stock plan (in shares) Stock Issued During Period, Shares, Share-based Compensation, Net of Forfeitures Common Stock Dividends (in shares) Common Stock Dividends, Shares Net issuance of common stock in connection with the acquisition of Diboll State Bancshares, Inc. (in shares) Stock Issued During Period, Shares, Acquisitions Business Combinations [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Diboll State Bancshares, Inc. Diboll State Bancshares, Inc. [Member] Diboll State Bancshares, Inc. [Member] Internal Credit Assessment [Axis] Internal Credit Assessment [Axis] Internal Credit Assessment [Domain] Internal Credit Assessment [Domain] Performing loans Performing Financial Instruments [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Fair Value at Acquisition Date Business Combination, Acquired Receivable, Fair Value Contractual Amounts Receivable Business Combination, Acquired Receivables, Gross Contractual Amount Cash Flows Not Expected to be Collected at Acquisition Date Business Combination, Acquired Receivables, Estimated Uncollectible Schedule of long-term debt by entity Schedule of long-term debt by entity [Table Text Block] [Table Text Block] for Schedule of long-term debt by entity [Table] Schedule of subordinated borrowing Schedule of Subordinated Borrowing [Table Text Block] Acquisition Business Combination Disclosure [Text Block] Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract] Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax [Abstract] Net (loss) gain Defined Benefit Plan, Accumulated Other Comprehensive Income (Loss), Gain (Loss), before Tax Prior service cost Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, Prior Service Cost (Credit), before Tax Accumulated other comprehensive (loss) income, before tax Defined Benefit Plan, Accumulated Other Comprehensive (Income) Loss, before Tax Deferred tax benefit (expense) Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Tax Pension and Other Postretirement Benefit Plans, Accumulated Other Comprehensive Income (Loss), Tax Reclassification of Certain Tax Effects Reclassification of Certain Tax Effects Reclassification of Certain Tax Effects Accumulated other comprehensive (loss) income, net of tax Accumulated Other Comprehensive (Income) Loss, Defined Benefit Plan, after Tax LOANS AND ALLOWANCE FOR PROBABLE LOAN LOSSES Loans, Notes, Trade and Other Receivables Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] OFF-BALANCE-SHEET ARRANGEMENTS, COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] FAIR VALUE MEASUREMENT Fair Value Disclosures [Text Block] Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year [Abstract] Defined Benefit Plan, Expected Amortization, Next Fiscal Year [Abstract] Net loss Pension and Other Postretirement Benefit Plans, Net Gains (Losses) that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Pension and Other Postretirement Benefit Plans, Net Gains (Losses) that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Prior service (credit) cost Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Pension and Other Postretirement Benefit Plans, Net Prior Service Cost (Credit) Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Total amount that will be amortized from accumulated other comprehensive income Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Before Tax Deferred tax benefit Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Tax Pension and Other Postretirement Benefit Plans, Amounts that Will be Amortized from Accumulated Other Comprehensive Income (Loss) in Next Fiscal Year, Tax Accumulated other comprehensive loss, net of tax Defined Benefit Plan, Expected Amortization, Next Fiscal Year Investments, Debt and Equity Securities [Abstract] Available-for-sale Securities, Amortized Cost Basis [Abstract] Available-for-sale Securities, Debt Maturities, Amortized Cost Basis, Fiscal Year Maturity [Abstract] Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Amortized Cost Basis Due after one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Amortized Cost Basis Due after five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Amortized Cost Basis Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Amortized Cost Basis Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Mortgage-backed Securities and Other Equity Securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Amortized Cost Basis Total Available-for-sale Debt Securities, Amortized Cost Basis Available-for-sale Securities, Fair Value [Abstract] Available-for-sale Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract] Due in one year or less Available-for-sale Securities, Debt Maturities, Next Twelve Months, Fair Value Due after one year through five years Available-for-sale Securities, Debt Maturities, Year Two Through Five, Fair Value Due after five years through ten years Available-for-sale Securities, Debt Maturities, Year Six Through Ten, Fair Value Due after ten years Available-for-sale Securities, Debt Maturities, after Ten Years, Fair Value Subtotal Available-for-sale Securities, Debt Maturities, Single Maturity Date Mortgage-backed Securities and Other Equity Securities Available-for-sale Securities, Debt Maturities, without Single Maturity Date, Fair Value Total Available-for-sale Securities Held to Maturity Securities, Carrying Value [Abstract] Held-to-maturity Securities, Debt Maturities, Net Carrying Amount [Abstract] Due in one year or less Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount Due after one year through five years Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount Due after five years through ten years Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount Due after ten years Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount Subtotal Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Amortized Cost Basis Mortgage-backed Securities Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Net Carrying Amount Carrying value Held-to-maturity Securities Held to Maturity Securities, Fair Value [Abstract] Held-to-maturity Securities, Debt Maturities, Fair Value, Fiscal Year Maturity [Abstract] Due in one year or less Held-to-maturity Securities, Debt Maturities, Next Twelve Months, Fair Value Due after one year through five years Held-to-maturity Securities, Debt Maturities, Year Two Through Five, Fair Value Due after five years through ten years Held-to-maturity Securities, Debt Maturities, Year Six Through Ten, Fair Value Due after ten years Held-to-maturity Securities, Debt Maturities, after Ten Years, Fair Value Subtotal Held-to-maturity Securities, Debt Maturities, Single Maturity Date, Fair Value Mortgage-backed Securities Held-to-maturity Securities, Debt Maturities, without Single Maturity Date, Fair Value Total Total held to maturities debt maturities by date and maturity date This item represents the total of all debt securities by maturity, at fair value, which are categorized as held-to-maturity. Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Loans and Leases Receivable Disclosure [Abstract] Loans and Leases Receivable Disclosure [Abstract] Total ending loans balance Loans and Leases Receivable, Gross Less: Allowance for loan losses Loans and Leases Receivable, Allowance Net loans Loans and Leases Receivable, Net Amount Loans acquired loans acquired carrying amount loans acquired carrying amount Allowance for loan loss recorded on PCI loans Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment, PCI Loans Financing Receivable, Allowance for Credit Losses, Individually Evaluated for Impairment, PCI Loans Contractually required principal and interest payments Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Contractually Required Payments Receivable at Acquisition Nonaccretable difference Certain Loans Acquired in Transfer, Nonaccretable Difference Cash flows expected to be collected Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, Cash Flows Expected to be Collected at Acquisition Accretable difference Certain Loans Acquired in Transfer, Accretable Yield Fair value of loans acquired with a deterioration of credit quality Certain Loans Acquired in Transfer Not Accounted for as Debt Securities, Acquired During Period, at Acquisition, at Fair Value Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Core deposits Core Deposits [Member] Trust Relationship Intangible Other Intangible Assets [Member] Noncompete Agreements Noncompete Agreements [Member] Acquisition, Acquiree [Domain] Percentage of company acquired Business Acquisition, Percentage of Voting Interests Acquired Number of branches Number of banking centers Number of branches Acquisition, number of shares issued Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Cash Payments to Acquire Businesses, Gross Company stock consideration, stock issued per each share of acquiree stock (in shares) Noncash or Part Noncash Acquisition, Company Stock Consideration, Per Each Share of Acquiree Stock, Shares Issued Noncash or Part Noncash Acquisition, Company Stock Consideration, Per Each Share of Acquiree Stock, Shares Issued Cash consideration, per share of acquiree stock (in dollars per share) Noncash or Part Noncash Acquisition, Cash Consideration, Per Each Share of Acquiree Stock Noncash or Part Noncash Acquisition, Cash Consideration, Per Each Share of Acquiree Stock Acquisition, closing stock price per share (in dollars per share) Business Acquisition, Share Price Acquisition, total merger consideration Business Combination, Consideration Transferred Acquisition, assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets Acquisition, loans Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Loans Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Loans Acquisition, investment securities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Marketable Securities Acquisition, liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities Acquisition, deposits Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deposits Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Deposits Acquisition, goodwill Goodwill Acquisition, finite-lived intangible assets Finite-lived Intangible Assets Acquired Amortization period Finite-Lived Intangible Assets, Remaining Amortization Period Acquisition expense Business Combination, Acquisition Related Costs Acquisition, legal and consulting fees Professional Fees Acquisition, software and data processing expense Information Technology and Data Processing Cost related to issuance of shares related to the merger Adjustments to Additional Paid in Capital, Stock Issued, Issuance Costs Pro forma net income (loss) Business Acquisition, Pro Forma Net Income (Loss) Pro forma revenue Business Acquisition, Pro Forma Revenue Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Financial institution counterparties Financial Institution Counterparties [Member] Financial Institution Counterparties [Member] Customer counterparties Customer Counterparties [Member] Customer Counterparties [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Derivatives designated as hedging instruments Designated as Hedging Instrument [Member] Derivatives designated as non-hedging instruments Not Designated as Hedging Instrument [Member] Hedging Relationship [Axis] Hedging Relationship [Axis] Hedging Relationship [Domain] Hedging Relationship [Domain] Cash Flow Hedging Cash Flow Hedging [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Notional Amount Derivative, Notional Amount Derivative Asset [Abstract] Derivative Asset [Abstract] Gross derivatives Derivative Asset, Fair Value, Gross Asset Offsetting derivative assets/liabilities Derivative Asset, Fair Value, Gross Liability Cash collateral received/posted Derivative Asset, Collateral, Obligation to Return Cash, Offset Net derivatives included in the consolidated balance sheets Derivative Asset Derivative Liability [Abstract] Derivative Liability [Abstract] Gross derivatives Derivative Liability, Fair Value, Gross Liability Offsetting derivative assets/liabilities Derivative Liability, Fair Value, Gross Asset Cash collateral received/posted Derivative Liability, Collateral, Right to Reclaim Cash, Offset Net derivatives included in the consolidated balance sheets Derivative Liability Net credit exposure Derivative Credit Risk Valuation Adjustment, Derivative Assets Schedule of accumulated other comprehensive income (loss) by component Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Reclassification out of Accumulated Other Comprehensive Income Reclassification out of Accumulated Other Comprehensive Income [Table Text Block] Schedule of Impaired Financing Receivable [Table] Schedule of Impaired Financing Receivable [Table] Financing Receivable, Impaired [Line Items] Financing Receivable, Impaired [Line Items] Impaired Financing Receivable, Recorded Investment [Abstract] Impaired Financing Receivable, Recorded Investment [Abstract] Unpaid Contractual Principal Balance Impaired Financing Receivable, Unpaid Principal Balance Recorded Investment Impaired Financing Receivable, with Related Allowance, Recorded Investment Related Allowance for Loan Losses Impaired Financing Receivable, Related Allowance PCI loans that experienced deterioration in credit quality subsequent to acquisition Purchase Credit Impaired Loans, with Deterioration in Credit Quality After Acquisition Purchase Credit Impaired Loans, with deterioration in credit qualify after acquisition LONG-TERM OBLIGATIONS Long-term Debt [Text Block] Condensed Financial Information of Parent Company Only Disclosure [Abstract] Schedule of Condensed Financial Statements [Table] Condensed Financial Statements [Table] Consolidated Entities [Axis] Consolidated Entities [Axis] Consolidated Entities [Domain] Consolidated Entities [Domain] Parent Parent Company [Member] Equity Method Investee, Name [Axis] Investment, Name [Axis] Equity Method Investee, Name [Domain] Investment, Name [Domain] Bank subsidiaries Bank Subsidiaries [Member] Bank Subsidiaries [Member] Nonbank subsidiaries Nonbank Subsidiaries [Member] Nonbank Subsidiaries [Member] Condensed Financial Statements, Captions [Line Items] Condensed Financial Statements, Captions [Line Items] ASSETS Assets [Abstract] Cash and due from banks Cash and Due from Banks Investment in subsidiaries at equity in underlying net assets Investment in Subsidiaries at Equity in Underlying Net Assets Investment in Subsidiaries at Equity in Underlying Net Assets Other assets Other Assets Total assets Assets Liabilities [Abstract] Liabilities [Abstract] Subordinated notes, net of unamortized debt issuance costs Subordinated Debt Trust preferred subordinated debentures, net of unamortized debt issuance costs Junior Subordinated Debenture Owed to Unconsolidated Subsidiary Trust Other liabilities Other Liabilities Total liabilities Liabilities Stockholders' Equity Attributable to Parent [Abstract] Stockholders' Equity Attributable to Parent [Abstract] Common stock: ($1.25 par value, 40,000,000 shares authorized, 37,802,352 shares issued at December 31, 2017 and 31,455,951 shares issued at December 31, 2016) Common Stock, Value, Issued Paid-in capital Additional Paid in Capital, Common Stock Retained earnings Retained Earnings (Accumulated Deficit) Treasury stock, at cost (2,802,019 at December 31, 2017 and 2,913,064 at December 31, 2016) Treasury Stock, Value Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total shareholders’ equity Total liabilities and shareholders’ equity Liabilities and Equity Schedule of Available-for-sale and Held to Maturity Securities [Table] Schedule of Available-for-sale and Held to Maturity Securities [Table] Schedule of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities and of all investments in certain debt and equity securities for which the entity has the positive intent and ability to hold until maturity. Residential Commercial Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] Schedule of Available-for-sale and Held-to-maturity Securities [Line Items] AVAILABLE FOR SALE: Available-for-sale Securities, Balance Sheet, Reported Amounts [Abstract] Amortized Cost Available-for-sale Securities, Amortized Cost Basis Gross unrealized gains, in OCI Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax Gross unrealized losses, in OCI Available-for-sale Securities, Accumulated Gross Unrealized Loss, before Tax Securities available for sale, at estimated fair value HELD TO MATURITY: Held-to-maturity Securities, Balance Sheet, Reported Amounts [Abstract] Amortized cost Held to Maturity Amortized Cost Basis Amortized cost basis before transfer from available for sale to held to maturity. Gross unrealized gains, in OCI Held To Maturity Securities Gross Unrealized Gains Recognized in Other Comprehensive Income Held To Maturity Securities Gross Unrealized Gains Recognized in Other Comprehensive Income Gross unrealized losses, in OCI Held To Maturity Securities Gross Unrealized Losses Recognized in OCI Held To Maturity Securities Gross Unrealized Losses Recognized in OCI Gross unrealized gains, not in OCI Held-to-maturity Securities, Accumulated Unrecognized Holding Gain Gross unrealized losses, not in OCI Held-to-maturity Securities, Accumulated Unrecognized Holding Loss Estimated fair value Held-to-maturity Securities, Fair Value Interest Income Recognized on Securities [Abstract] Interest and Other Income [Abstract] U.S. Treasury Interest Income, Securities, US Treasury U.S. Government Agency Debentures Interest Income, Securities, Other US Government State and Political Subdivisions Interest Income, Securities, State and Municipal Other Stocks and Bonds Interest Income, Other Stocks and Bonds Represents interest income, including any amortization and accretion (as applicable) of discounts and premiums, derived from securities backed by other stocks and bonds. Other Equity Securities Interest income, Other Equity Securities Interest income on other equity securities Mortgage-backed Securities Interest Income, Securities, Mortgage Backed Total interest income on securities Interest and Other Income Scheduled maturities of unused commitments Schedule of Fair Value, Off-balance Sheet Risks [Table Text Block] Future minimum commitments of non-cancelable operating leases Lessee, Operating Lease, Disclosure [Table Text Block] Schedule of future minimum rental payments receivable under non-cancelable operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Payments for Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income to net cash provided by operations: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and net amortization Depreciation, Depletion and Amortization Securities premium amortization (discount accretion), net Accretion (Amortization) of Discounts and Premiums, Investments Loan (discount accretion) premium amortization, net Investment Income, Net, Amortization of Discount and Premium Provision for loan losses Provision for Loan and Lease Losses Stock compensation expense Share-based Compensation Deferred tax expense (benefit) Deferred Income Tax Expense (Benefit) Net tax benefit related to stock awards Excess Tax Benefit from Share-based Compensation, Operating Activities Net gain on sale of securities available for sale Available-for-sale Securities, Gross Realized Gain (Loss), Excluding Other than Temporary Impairments Net loss on premises and equipment Gain (Loss) on Disposition of Property Plant Equipment, Excluding Oil and Gas Property and Timber Property Gross proceeds from sales of loans held for sale Proceeds from Sale of Mortgage Loans Held-for-sale Gross originations of loans held for sale Payments for Origination and Purchases of Loans Held-for-sale Net loss on other real estate owned Gains (Losses) on Sales of Other Real Estate Net gain on sale of customer receivables Gain (Loss) on Sale of Notes Receivable Net change in: Increase (Decrease) in Operating Capital [Abstract] Interest receivable Increase (Decrease) in Accrued Interest Receivable, Net Other assets Increase (Decrease) in Other Operating Assets Interest payable Increase (Decrease) in Interest Payable, Net Other liabilities Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Securities available for sale: Available-for-sale Securities [Abstract] Purchases Payments to Acquire Available-for-sale Securities Sales Proceeds from Sale of Available-for-sale Securities Maturities, calls and principal repayments Proceeds from Maturities, Prepayments and Calls of Available-for-sale Securities Securities held to maturity: Held-to-maturity Securities [Abstract] Purchases Payments to Acquire Held-to-maturity Securities Maturities, calls and principal repayments Proceeds from Maturities, Prepayments and Calls of Held-to-maturity Securities Proceeds from redemption of FHLB stock and other investments Proceeds from Sale of Federal Reserve Bank Stock Purchases of FHLB stock and other investments Payments to Acquire Federal Reserve Bank Stock Net loan originations Payments for (Proceeds from) Loans and Leases Proceeds from sales of customer receivables Proceeds from Sale of Notes Receivable Net cash and cash equivalents acquired in acquisition Cash Acquired from Acquisition Net cash paid in acquisition Purchases of premises and equipment Payments to Acquire Property, Plant, and Equipment Proceeds from sales of premises and equipment Proceeds from Sale of Property, Plant, and Equipment Proceeds from sales of other real estate owned Proceeds from Sale of Wholly Owned Real Estate and Real Estate Acquired in Settlement of Loans Proceeds from sales of repossessed assets Proceeds from Sale of Foreclosed Assets Net cash provided by (used in) investing activities Net Cash Provided by (Used in) Investing Activities FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Net change in deposits Net Change Interest and Noninterest-bearing Deposits, Domestic Net increase (decrease) in federal funds purchased and repurchase agreements Increase (Decrease) in Federal Funds Purchased and Securities Sold under Agreements to Repurchase, Net Proceeds from FHLB borrowings Proceeds from Federal Home Loan Bank Borrowings Repayment of FHLB borrowings Repayments of Federal Home Loan Bank Borrowings Net proceeds from issuance of subordinated long-term debt Proceeds from Issuance of Subordinated Long-term Debt Tax benefit related to stock awards Excess Tax Benefit from Share-based Compensation, Financing Activities Proceeds from stock option exercises Proceeds from Stock Options Exercised Cash paid to tax authority from stock option exercises Cash paid to tax authority from stock option exercises Cash paid to tax authority from stock option exercises Purchase of common stock Payments for Repurchase of Common Stock Proceeds from the issuance of common stock for dividend reinvestment plan Proceeds from Issuance of Common Stock, Dividend Reinvestment Plan Proceeds from the issuance of common stock Proceeds from Issuance of Common Stock Cash dividends paid Payments of Ordinary Dividends, Common Stock Payments for other financing activities Payments of Merger Related Costs, Financing Activities Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period SUPPLEMENTAL DISCLOSURES FOR CASH FLOW INFORMATION: Supplemental Cash Flow Information [Abstract] Interest paid Interest Paid Income taxes paid Income Taxes Paid SUPPLEMENTAL DISCLOSURES OF NONCASH INVESTING AND FINANCING ACTIVITIES: Noncash Investing and Financing Items [Abstract] Loans transferred to other repossessed assets and real estate through foreclosure Loans transferred to other repossessed assets and real estate through foreclosure The acquisition of assets and real estate received in full or partial satisfaction of a receivable including real and personal property; equity interests in corporations, partnerships, and joint ventures; and beneficial interests in trusts. Transfer of available for sale securities to held to maturity securities Securities Transferred From Available for Sale to Held to Maturity Securities Transferred From Available for Sale to Held to Maturity Adjustment to pension liability Adjustment to pension liability Net changes to pension liability during the period related to benefit plans, after tax. Stock dividend (2.5%, 5% and 5%, respectively) Dividends, Stock Unsettled trades to purchase securities Unsettled Trades to Purchase Securities Liability Amount of securities purchased that were not settled by the end of the period. The amount recorded is the purchase price including any accrued interest. This asset is collected upon delivery of the securities. Unsettled trades to sell securities Unsettled Trades to Sell Securities Amount of securities sold that were not settled by the end of the period. The amount recorded is the selling price including any accrued interest. This asset is collected upon delivery of the securities. Common stock issued in acquisition Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Investment securities: Investment securities: [Abstract] -- None. No documentation exists for this element. -- Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Less than 12 months, fair value Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value More than 12 months, fair value Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Total fair value Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract] Available-for-sale Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract] Less than 12 months, unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss More than 12 months, unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Unrealized loss position Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss Mortgage-backed securities: Mortgage Backed Securities [Abstract] Mortgage Backed Securities [Abstract] Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value [Abstract] Less than 12 months, fair value Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value More than 12 months, fair value Held-to-maturity Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value Total fair value Held-to-maturity Securities, Continuous Unrealized Loss Position, Fair Value Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Losses [Abstract] Held-to-maturity Securities, Continuous Unrealized Loss Position, Aggregate Loss [Abstract] Less than 12 Months, unrealized loss position Held-to-maturity Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss More than 12 Months, unrealized loss position Held-to-maturity Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss Unrealized loss position Held-to-maturity Securities, Continuous Unrealized Loss Position, Accumulated Loss Accounting Policies [Abstract] Basis of Presentation and Consolidation Consolidation, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Business Combinations Business Combinations Policy [Policy Text Block] Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Basic and Diluted Earnings per Common Share Earnings Per Share, Policy [Policy Text Block] Comprehensive Income Comprehensive Income, Policy [Policy Text Block] Loans Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block] Loans Held For Sale Finance, Loan and Lease Receivables, Held-for-sale, Policy [Policy Text Block] Loan Fees Loans and Leases Receivable, Origination Fees, Discounts or Premiums, and Direct Costs to Acquire Loans Policy [Policy Text Block] Allowance for Loan Losses Loans and Leases Receivable, Allowance for Loan Losses Policy [Policy Text Block] Nonaccrual Loans Loans and Leases Receivable, Nonaccrual Loan and Lease Status, Policy [Policy Text Block] Other Real Estate Owned Loans and Leases Receivable, Real Estate Acquired Through Foreclosure, Policy [Policy Text Block] Foreclosed Assets Finance, Loan and Lease Receivables, Held for Investments, Foreclosed Assets Policy [Policy Text Block] Securities Marketable Securities, Policy [Policy Text Block] Securities with Limited Marketability Securities Owned Not Readily Marketable, Policy [Policy Text Block] Premises and Equipment Property, Plant and Equipment, Policy [Policy Text Block] Bank Owned Life Insurance Bank Owned Life Insurance [Policy Text Block] Bank Owned Life Insurance [Policy Text Block] Goodwill and Other Intangibles Goodwill and Intangible Assets, Policy [Policy Text Block] Repurchase Agreements Repurchase and Resale Agreements Policy [Policy Text Block] Derivative Financial Instruments and Hedging Activities Derivatives, Policy [Policy Text Block] Terminated Derivative Financial Instruments Derivatives, Hedge Discontinuances, Termination of Hedging Instrument or Hedged Item [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Advertising Costs Advertising Cost, Policy, Expensed Advertising Cost [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Fair Value of Financial Instruments Fair Value of Financial Instruments, Policy [Policy Text Block] Defined Benefit Pension Plan Pension and Other Postretirement Plans, Pensions, Policy [Policy Text Block] Share-Based Awards Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Loss Contingencies Commitments and Contingencies, Policy [Policy Text Block] Trust Assets Assets, Trust Assets, Policy [Policy Text Block] Disclosure of accounting policy for reporting trust assets. Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Deposits [Abstract] Deposit Liabilities Components [Table] Deposit Liabilities Components [Table] Deposit Liabilities Components [Table] Deposits, by Customer, Alternative [Axis] Deposits, by Customer, Alternative [Axis] Deposits, by Customer, Alternative [Axis] Deposits, by Customer, Alternative [Domain] Deposits, by Customer, Alternative [ [Domain] Deposits, by Customer, Alternative [Domain] Private accounts Private Accounts [Member] Private Accounts [Member] Public accounts Public Accounts [Member] Public Accounts [Member] Deposit Liabilities Components [Line Items] Deposit Liabilities Components [Line Items] [Line Items] for Deposit Liabilities Components [Table] Deposits, by Component, Alternative [Abstract] Deposits, by Component, Alternative [Abstract] Noninterest bearing demand deposits: Noninterest-bearing Deposit Liabilities, by Component [Abstract] Noninterest bearing demand deposits Noninterest-bearing Deposit Liabilities, Domestic Interest bearing deposits: Interest-bearing Deposit Liabilities, by Component [Abstract] Savings deposits Interest-bearing Domestic Deposit, Savings Money market demand deposits Interest-bearing Domestic Deposit, Money Market Platinum money market deposits Interest-bearing Domestic Deposit, Money Market, Platinum Interest-bearing Domestic Deposit, Money Market, Platinum Interest bearing checking Interest-bearing Domestic Deposit, Checking, Premier Business Checking Interest-bearing Domestic Deposit, Checking, Premier Business Checking NOW demand deposits Interest-bearing Domestic Deposit, Negotiable Order of Withdrawal (NOW) Certificates and other time deposits, $250,000 or more Certificates and other time deposits, $250,000 or more Certificates and TIme Deposits, $250,000 or more, Domestic Certificates and other time deposits under $250,000 Time Deposits, Less than $250,000, Domestic Time Deposits, Less than $250,000, Domestic Total interest bearing deposits Interest-bearing Deposit Liabilities, Domestic Total deposits Deposits EMPLOYEE BENEFITS Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Text Block] Employee Benefits Including Defined Benefit Plans and Share-based Compensation Plans [Text Block] Property, Plant and Equipment [Abstract] Premises Buildings and Improvements, Gross Furniture and equipment Furniture and Fixtures, Gross Premises and equipment, gross Property, Plant and Equipment, Gross Less: accumulated depreciation Accumulated Depreciation, Depletion and Amortization, Property, Plant, and Equipment Premises and equipment, net Property, Plant and Equipment, Net Depreciation [Abstract] Depreciation [Abstract] Accumulated depreciation of assets written off Accumulated Depreciation, Depletion and Amortization, Sale or Disposal of Property, Plant and Equipment Depreciation expense Depreciation Dividend Reinvestment and Common Stock Repurchase Plan [Abstract] Dividend Reinvestment and Common Stock Repurchase Plan [Abstract] DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN DIVIDEND REINVESTMENT AND COMMON STOCK REPURCHASE PLAN [Text Block] Total disclosure about dividend reinvestment and common stock purchase plan. Schedule of Financing Receivable, Recorded Investment, Credit Quality Indicator [Table] Schedule of Financing Receivable, Recorded Investment, Credit Quality Indicator [Table] Pass Pass [Member] Pass Watch Pass Watch [Member] A category of financing receivables not considered to be special mention, substandard, doubtful, and loss receivables. Special Mention Special Mention [Member] Substandard Substandard [Member] Doubtful Doubtful [Member] Financing Receivable, Recorded Investment [Line Items] Financing Receivable, Recorded Investment [Line Items] Financing Receivable, Recorded Investment, Credit Quality Indicator [Abstract] Financing Receivable Recorded Investment By Credit Quality Indicator [Abstract] -- None. No documentation exists for this element. -- Total ending loan balance PCI loans ACCUMULATED OTHER COMPREHENSIVE LOSS Comprehensive Income (Loss) Note [Text Block] Nonperforming Assets by Asset Class [Abstract] Nonperforming Assets [Abstract] -- None. No documentation exists for this element. -- Accruing loans past due more than 90 days Financing Receivable, Recorded Investment, 90 Days Past Due and Still Accruing Restructured loans Financing Receivable, Modifications, Recorded Investment Other real estate owned Real Estate Acquired Through Foreclosure Repossessed assets Other Repossessed Assets Total Nonperforming Assets Nonperforming Assets Nonperforming Assets PCI loans restructured Purchase Credit Impaired Loans Restructured Purchase Credit Impaired Loans Restructured Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract] Service cost Defined Benefit Plan, Service Cost Interest cost Defined Benefit Plan, Interest Cost Expected return on assets Defined Benefit Plan, Expected Return (Loss) on Plan Assets Net loss amortization Defined Benefit Plan, Amortization of Gain (Loss) Prior service cost (credit) amortization Defined Benefit Plan, Amortization of Prior Service Cost (Credit) Special and contractual termination benefits Defined Benefit Plan, Benefit Obligation, Special and Contractual Termination Benefits Loss (gain) recognized due to settlement Net periodic benefit cost Defined Benefit Plan, Net Periodic Benefit Cost (Credit) Other Commitments [Abstract] Long-term Purchase Commitment [Table] Long-term Purchase Commitment [Table] Premises and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Premises and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Land, Buildings and Improvements Land, Buildings and Improvements [Member] Office Equipment Office Equipment [Member] Long-term Purchase Commitment [Line Items] Long-term Purchase Commitment [Line Items] Rent expense Operating Leases, Rent Expense, Net Number of square feet in building acquired Building Acquired, Number of Square Feet Building Acquired, Number of Square Feet Number of square feet occupied Number of Square Feet Occupied Number of Square Feet Occupied Lease revenue Operating Leases, Income Statement, Lease Revenue Securities Available-for-sale Securities and Held-to-maturity Securities [Abstract] Unsettled trades to purchase securities Unsettled trades to sell securities Deposits [Abstract] Unsettled issuances of brokered cds Unsettled Issuances of Brokered CDs Amount of brokered CDs sold that were not settled by the end of the period. The amount recorded is the selling price including any accrued interest. Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years 2021 Operating Leases, Future Minimum Payments, Due in Four Years 2022 Operating Leases, Future Minimum Payments, Due in Five Years 2023 and thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total future minimum payments due Operating Leases, Future Minimum Payments Due Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Stock options Employee Stock Option [Member] Exercise Price Range [Axis] Exercise Price Range [Axis] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Domain] $14.67 - $20.00 Range One [Member] Range One [Member] $20.01 - $25.00 Range Two [Member] Range Two [Member] $25.01 - $30.00 Range Three [Member] Range Three [Member] $30.01 - $35.00 Range Four [Member] [Member] Range Four $35.01 - $37.28 Range Five [Member] Range Five [Member] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] Range of Exercise Prices - Lower Range Limit (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Lower Range Limit Range of Exercise Prices - Upper Range Limit (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Upper Range Limit Options Outstanding Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Options Outstanding [Abstract] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Options Outstanding [Abstract] Number of Shares (in shares) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Outstanding Options Weighted- Average Exercise Price (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Exercise Price Weighted- Average Remaining Contractual Life in Years Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Outstanding Options, Weighted Average Remaining Contractual Term Options Exercisable Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Options Exercisable [Abstract] Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Options Exercisable [Abstract] Number of Shares (in shares) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Number of Exercisable Options Weighted- Average Exercise Price (in dollars per share) Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range, Exercisable Options, Weighted Average Exercise Price Regulatory Capital Requirements [Abstract] SHAREHOLDERS' EQUITY Regulatory Capital Requirements under Banking Regulations [Text Block] SECURITIES Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block] Schedule of Fair Value, Off-balance Sheet Risks [Table] Schedule of Fair Value, Off-balance Sheet Risks [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Commitments to extend credit Commitments to Extend Credit [Member] Standby letters of credit Standby Letters of Credit [Member] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Axis] Guarantor Obligations, Nature [Domain] Guarantor Obligations, Nature [Domain] Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items] Financial instruments with off-balance sheet risk, at fair value Fair Value Disclosure, Off-balance Sheet Risks, Amount, Liability DERIVATIVES INSTRUMENTS AND HEDGING ACTIVITIES DISCLOSURE Derivative Instruments and Hedging Activities Disclosure [Text Block] Line of Credit Facility [Table] Line of Credit Facility [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Three-Month London Interbank Offered Rate (LIBOR) Three-Month London Interbank Offered Rate (LIBOR) [Member] Three-Month London Interbank Offered Rate (LIBOR) [Member] One-Month London Interbank Offered Rate (LIBOR) One-Month London Interbank Offered Rate (LIBOR) [Member] One-Month London Interbank Offered Rate (LIBOR) [Member] Variable Rate Advance Agreements Variable Rate Advance Agreements [Member] Variable Rate Advance Agreements [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Lender Name [Axis] Line of Credit Facility, Lender [Domain] Frost Bank Frost Bank [Member] Frost Bank [Member] TIB - The Independent Bankers Bank TIB - The Independent Bankers Bank [Member] TIB - The Independent Bankers Bank [Member] Comerica Bank Comerica Bank [Member] Comerica Bank [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Federal home loan bank, advances, general debt obligations, disclosures, interest rate at period end Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Interest Rate at Period End Maturity range of FHLB advances Federal Home Loan Bank, Advances, Maturities Summary, Maturity Range Represents the range of years until maturity from lowest to highest that are applicable to Federal Home Loan Bank outstanding as of the balance sheet date. Debt face amount Debt Instrument, Face Amount Number of variable rate advance agreements Debt Instrument, Number Of Variable Rate Advance Agreements Debt Instrument, Number Of Variable Rate Advance Agreements Description of variable rate basis Debt Instrument, Description of Variable Rate Basis Basis spread on variable rate Debt Instrument, Basis Spread on Variable Rate Derivative, fixed interest rate Derivative, Fixed Interest Rate Derivative, term of contract Derivative, Term of Contract Derivative, instruments terminated Derivative, instruments terminated Derivative, instruments terminated Derivative, terminated, notional amount Derivative, terminated, notional amount Derivative, terminated, notional amount Number of credit lines maintained by the Company Line of Credit Facility, Number of Credit Lines Maintained by the Company Line of Credit Facility, Number of Credit Lines Maintained by the Company Line of credit, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Federal funds purchased Federal Funds Purchased Line of credit facility, capacity available for issuance of letters of credit Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases Number of outstanding letters of credit Number of outstanding letters of credit Number of Outstanding Letters of Credit Letters of credit outstanding Letters of Credit Outstanding, Amount FHLB Advances, unused funds Federal Home Loan Bank, Advances, General Debt Obligations, Amount of Available, Unused Funds Letters of credit, FHLB, as collateral Letters of Credit, FHLB, as Collateral The amount of letters of credit outstanding at year end from the Federal Home Loan Bank as collateral for its public fund deposits. Securities sold under agreements to repurchase Securities Sold under Agreements to Repurchase Maturity of repurchase agreements Repurchase Agreement Counterparty, Maturity of Agreements Repurchase Agreement Counterparty, Maturity of Agreements Defined Benefit Plan, Expected Future Benefit Payment [Abstract] Defined Benefit Plan, Expected Future Benefit Payment [Abstract] 2018 Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months 2019 Defined Benefit Plan, Expected Future Benefit Payment, Year Two 2020 Defined Benefit Plan, Expected Future Benefit Payment, Year Three 2021 Defined Benefit Plan, Expected Future Benefit Payment, Year Four 2022 Defined Benefit Plan, Expected Future Benefit Payment, Year Five 2023 through 2027 Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter Total expected future payments Defined Benefit Plan, Expected Future Benefit Payments Defined Benefit Plan, Expected Future Benefit Payments Change in Projected Benefit Obligation: Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] Benefit obligation at end of prior year Defined Benefit Plan, Benefit Obligation Actuarial loss (gain) Defined Benefit Plan, Benefit Obligation, Actuarial Gain (Loss) Benefits Paid Defined Benefit Plan, Benefit Obligation, Benefits Paid Expenses paid Defined Benefit Plan, Plan Assets, Administration Expense Plan Amendments Defined Benefit Plan, Benefit Obligation, Increase (Decrease) for Plan Amendment Settlements Defined Benefit Plan, Benefit Obligation, (Increase) Decrease for Settlement Special and contractual termination benefits Benefit obligation at end of year Change in Plan Assets: Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] Fair value of plan assets at end of prior year Defined Benefit Plan, Fair Value of Plan Assets Actual return Defined Benefit Plan, Plan Assets, Increase (Decrease) for Actual Return (Loss) Employer contributions Defined Benefit Plan, Plan Assets, Contributions by Employer Benefits paid Defined Benefit Plan, Plan Assets, Benefits Paid Expenses paid Settlements Defined Benefit Plan, Plan Assets, Payment for Settlement Fair value of plan assets at end of year (Un)Funded status at end of year Defined Benefit Plan, Funded (Unfunded) Status of Plan Accrued benefit (liability) asset recognized Defined Benefit Plan, Amounts for Asset (Liability) Recognized in Statement of Financial Position Accumulated benefit obligation at end of year Defined Benefit Plan, Accumulated Benefit Obligation Business Combination, Segment Allocation [Table] Business Combination, Segment Allocation [Table] Business Combination Segment Allocation [Line Items] Business Combination Segment Allocation [Line Items] Assets of acquired bank: Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets [Abstract] Cash, cash equivalents, and amounts due from banks Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Other investments Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Investments Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Assets, Other Investments Securities available for sale Loans Property and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment Other assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Other Noncurrent Assets Core deposit intangible Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Trust relationship intangible Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles Goodwill Liabilities of acquired bank: Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities [Abstract] Deposits Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Financial Liabilities Deferred tax liability, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities Noncurrent Other liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities, Other Fair value of assets acquired net of liabilities assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Financing Receivables, Period Past Due [Axis] Financing Receivables, Period Past Due [Axis] Financing Receivables, Period Past Due [Domain] Financing Receivables, Period Past Due [Domain] 30-59 Days Past Due Financing Receivables, 30 to 59 Days Past Due [Member] 60-89 Days Past Due Financing Receivables, 60 to 89 Days Past Due [Member] Greater than 90 Days Past Due Financing Receivables, Equal to Greater than 90 Days Past Due [Member] Total Past Due Financing Receivable, Recorded Investment, Past Due Current Financing Receivable, Recorded Investment, Current Allowance for Loan Losses, Loan Balance, By Impairment Method [Abstract] Allowance for Loan Losses, Loan Balance, By Impairment Method [Abstract] Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Table] Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Table] Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Table] Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items] Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Line Items] [Line Items] for Schedule of Allowance For Loan Losses, Loan Balance, by Impairment Method [Table] Loans individually evaluated for impairment Financing Receivable, Individually Evaluated for Impairment Loans collectively evaluated for impairment Financing Receivable, Collectively Evaluated for Impairment Purchased credit impaired loans Quarterly Financial Information Disclosure [Abstract] Schedule of quarterly financial information Quarterly Financial Information [Table Text Block] Balance Sheet-Parentheticals [Abstract] Balance Sheet-Parentheticals [Abstract] Statement [Table] Statement [Table] Statement [Line Items] Statement [Line Items] Common stock, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common stock, shares authorized (in shares) Common Stock, Shares Authorized Common stock, shares issued (in shares) Common Stock, Shares, Issued Treasury stock, (in shares) Treasury Stock, Shares PARENT COMPANY FINANCIAL INFORMATION Condensed Financial Information of Parent Company Only Disclosure [Text Block] Level 1 Level 2 Defined Benefit Plan, Asset Categories [Axis] Defined Benefit Plan, Asset Categories [Axis] Plan Asset Categories [Domain] Plan Asset Categories [Domain] Cash Cash [Member] Cash equivalents Cash Equivalents [Member] Equity Securities U.S. large cap equities United States Large Cap Equities [Member] United States Large Cap Equities [Member] U.S. mid cap equities United States Mid Cap Equities [Member] United States Mid Cap Equities [Member] U.S. small cap equities United States Small Cap Equities [Member] United States Small Cap Equities [Member] International International [Member] International Equities [Member] Fixed Income Securities Fixed Income Securities [Member] Corporate bonds Corporate Bond Securities [Member] International developed International Developed Equities [Member] International Developed Equities [Member] International emerging International Emerging Equities [Member] International Emerging Equities [Member] U.S. government agencies Municipal bonds Municipal Bonds [Member] U.S. agency mortgage-backed securities Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] Asset-backed Securities Asset-backed Securities [Member] Real Estate Real Estate Funds [Member] Balanced Asset Allocation Balanced Asset Allocation [Member] Balanced Asset Allocation [Member] - comprised of a combination of fixed income and equity investment options. Other Other [Member] Other [Member] - comprised of a broad range of instruments including, but not limited to, equities, bonds, currencies, convertible securities and derivatives such as futures, options, swaps and forwards. Defined Benefit Plan, Categories of Plan Assets [Abstract] Defined Benefit Plan, Information about Plan Assets [Abstract] Total fair value of plan assets Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Incentive Plan 2009 Incentive Plan 2009 [Member] Name of the equity-based compensation arrangement plan. Award Type [Domain] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Weighted-average grant date fair value per option (in dollars per share) Share-based Compensation, Weighted-Average Grant Date Fair Value The Share-based compensation, weighted-average grant date fair value per option, for grants during the period. Weighted-average assumptions: Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions and Methodology [Abstract] Risk-free interest rates Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected volatility factors of the market price of Southside Bancshares common stock Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected option life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] 5.50% Subordinated Notes 5.50% Subordinated Notes Due 2026 [Member] 5.50% Subordinated Notes Due 2026 Southside Statutory Trust III Southside Statutory Trust III, net of unamortized debt issuance costs [Member] Debt obligations for Southside Statutory Trust III. Southside Statutory Trust IV Southside Statutory Trust IV [Member] Debt obligation for Southside Statutory Trust IV. Southside Statutory Trust V Southside Statutory Trust V [Member] Debt obligation for Southside Statutory Trust V. Magnolia Trust Company I Magnolia Trust Company I [Member] Debt obligation for Magnolia Trust Company I. LIBOR London Interbank Offered Rate (LIBOR) [Member] Amount issued Aggregate principal amount of subordinated notes Aggregate principal amount of subordinated notes Other long-term debt Other Long-term Debt Stated interest rate Debt Instrument, Interest Rate, Stated Percentage Coupon Rate Debt Instrument, Interest Rate, Effective Percentage Basis spread on variable rate, effective September 30, 2021 Debt Instrument, Basis Spread on Variable Rate, effective September 30, 2021 Debt Instrument, Basis Spread on Variable Rate, effective September 30, 2021 Available for sale securities, transferred to held to maturity, unrealized loss Available For Sale Securities, Transferred To Held To Maturity Securities, Unrealized Loss, Before Tax The gross unrealized gain(loss) on available for sale securities transferred to held to maturity during the period. Available for sale securities, transferred to held to maturity, unrealized loss, net of tax Available For Sale Securities, Transferred To Held To Maturity Securities, Unrealized Loss, Net Of Tax The unrealized gain(loss) included in investments for those available for sale securities transferred to held to maturity securities, net of tax. Proceeds from sale of held-to-maturity securities Proceeds from Sale of Held-to-maturity Securities Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] Available-for-sale Securities, Gross Realized Gain (Loss) [Abstract] Realized losses Available-for-sale Securities, Gross Realized Losses Realized gains Available-for-sale Securities, Gross Realized Gains Net securities gains from AFS portfolio Available-for-sale Securities, Gross Realized Gain (Loss) Securities pledged as collateral, carrying value Pledged Financial Instruments, Not Separately Reported, Securities Statement of Financial Position [Abstract] Held to Maturity, fair value Time Deposits, Fiscal Year Maturity [Abstract] Time Deposits, Fiscal Year Maturity [Abstract] 2018 Time Deposit Maturities, Next Twelve Months 2019 Time Deposit Maturities, Year Two 2020 Time Deposit Maturities, Year Three 2021 Time Deposit Maturities, Year Four 2022 Time Deposit Maturities, Year Five 2023 and thereafter Time Deposit Maturities, after Year Five Total Time Deposits Common Stock Common Stock [Member] Paid In Capital Additional Paid-in Capital [Member] Retained Earnings Retained Earnings [Member] Treasury Stock Treasury Stock [Member] Accumulated Other Comprehensive Income (Loss) Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Net Income Other comprehensive income (loss) Other Comprehensive Income (Loss), Net of Tax Issuance of common stock for dividend reinvestment plan (43,650 shares in 2017, 44,575 shares in 2016, 49,908 shares in 2015) Stock Issued During Period, Value, Dividend Reinvestment Plan Net issuance of common stock (2,185,000 shares) Stock Issued During Period, Value, New Issues Net issuance of common stock in connection with the acquisition of Diboll State Bancshares, Inc. (5,534,925 shares) Stock Issued During Period, Value, Acquisitions Purchase of common stock (443,426 shares) Treasury Stock, Value, Acquired, Cost Method