$SBSI
SOUTHSIDE BANCSHARES INC Stock $sbsi

$sbsi Overview Financials Valuation SEC Filings Company Website

2020 Q4 Form 10-K Financial Statement

#000070543221000013 Filed on February 26, 2021

Income Statement

Concept	2020 Q4	2019 Q4	2019 Q3
Revenue	$56.90M	$60.53M	$60.56M
YoY Change	-6.0%	4.33%	5.95%
Cost Of Revenue
YoY Change
Gross Profit
YoY Change
Gross Profit Margin
Selling, General & Admin
YoY Change
% of Gross Profit
Research & Development
YoY Change
% of Gross Profit
Depreciation & Amortization	$3.000M	$3.000M	$3.000M
YoY Change	0.0%	-11.76%	-14.29%
% of Gross Profit
Operating Expenses
YoY Change
Operating Profit
YoY Change
Interest Expense	$8.197M	$17.36M	$18.18M
YoY Change	-52.77%	11.18%	23.33%
% of Operating Profit
Other Income/Expense, Net
YoY Change
Pretax Income	$33.84M	$20.19M	$23.45M
YoY Change	67.6%	1.44%	4.26%
Income Tax	$4.265M	$2.854M	$3.661M
% Of Pretax Income	12.6%	14.14%	15.61%
Net Earnings	$29.57M	$17.34M	$19.79M
YoY Change	70.59%	-0.26%	-2.52%
Net Earnings / Revenue	51.97%	28.64%	32.68%
Basic Earnings Per Share	$0.89	$0.51	$0.59
Diluted Earnings Per Share	$0.89	$0.51	$0.58
COMMON SHARES
Basic Shares Outstanding	33.07M shares	33.77M shares	33.77M shares
Diluted Shares Outstanding			33.90M shares

Balance Sheet

Concept	2020 Q4	2019 Q4	2019 Q3
SHORT-TERM ASSETS
Cash & Short-Term Investments
YoY Change
Cash & Equivalents	$108.4M	$110.7M	$114.8M
Short-Term Investments
Other Short-Term Assets
YoY Change
Inventory
Prepaid Expenses
Receivables
Other Receivables
Total Short-Term Assets
YoY Change
LONG-TERM ASSETS
Property, Plant & Equipment	$144.6M	$143.9M	$141.7M
YoY Change	0.46%	5.84%	5.78%
Goodwill	$201.1M	$201.1M	$201.1M
YoY Change	0.0%	0.0%	-0.01%
Intangibles	$9.744M	$13.36M	$14.39M
YoY Change	-27.07%	-24.85%	-24.29%
Long-Term Investments	$11.90M	$12.30M	$12.40M
YoY Change	-3.25%	1.65%
Other Assets		$0.00	$0.00
YoY Change		-100.0%	-100.0%
Total Long-Term Assets
YoY Change
TOTAL ASSETS
Total Short-Term Assets
Total Long-Term Assets
Total Assets	$7.008B	$6.749B	$6.542B
YoY Change	3.84%	10.21%	7.15%
SHORT-TERM LIABILITIES
YoY Change
Accounts Payable
YoY Change
Accrued Expenses	$16.70M	$10.20M	$10.50M
YoY Change	63.73%
Deferred Revenue
YoY Change
Short-Term Debt	$23.20M	$28.40M	$9.600M
YoY Change	-18.31%	-22.83%	6.67%
Long-Term Debt Due
YoY Change
Total Short-Term Liabilities	$16.70M	$10.20M	$10.50M
YoY Change	63.73%	-72.28%	16.67%
LONG-TERM LIABILITIES
Long-Term Debt	$257.5M	$158.8M	$158.8M
YoY Change	62.15%	0.06%	0.13%
Other Long-Term Liabilities	$55.10M	$66.60M	$75.00M
YoY Change	-17.27%	26.62%	6.38%
Total Long-Term Liabilities	$312.6M	$225.4M	$233.8M
YoY Change	38.69%	6.67%	2.05%
TOTAL LIABILITIES
Total Short-Term Liabilities	$16.70M	$10.20M	$10.50M
Total Long-Term Liabilities	$312.6M	$225.4M	$233.8M
Total Liabilities	$6.133B	$5.944B	$5.732B
YoY Change	3.17%	10.24%	7.08%
SHAREHOLDERS EQUITY
Retained Earnings	$111.2M	$80.27M	$74.48M
YoY Change	38.54%	23.89%	27.14%
Common Stock	$818.9M	$814.1M	$812.9M
YoY Change	0.6%	0.53%	0.49%
Preferred Stock
YoY Change
Treasury Stock (at cost)	$123.9M	$94.01M	$93.57M
YoY Change	31.82%	1.02%	103.57%
Treasury Stock Shares	4.984M shares	4.064M shares	4.083M shares
Shareholders Equity	$875.3M	$804.6M	$810.5M
YoY Change
Total Liabilities & Shareholders Equity	$7.008B	$6.749B	$6.542B
YoY Change	3.84%	10.21%	7.15%

Cashflow Statement

Concept	2020 Q4	2019 Q4	2019 Q3
OPERATING ACTIVITIES
Net Income	$29.57M	$17.34M	$19.79M
YoY Change	70.59%	-0.26%	-2.52%
Depreciation, Depletion And Amortization	$3.000M	$3.000M	$3.000M
YoY Change	0.0%	-11.76%	-14.29%
Cash From Operating Activities	$40.20M	$20.60M	$25.20M
YoY Change	95.15%	6.74%	-22.7%
INVESTING ACTIVITIES
Capital Expenditures	-$1.200M	-$4.500M	-$3.500M
YoY Change	-73.33%	0.0%	-5.41%
Acquisitions
YoY Change
Other Investing Activities	$201.2M	-$213.4M	-$180.1M
YoY Change	-194.28%	244.75%	-277.26%
Cash From Investing Activities	$200.1M	-$217.8M	-$183.7M
YoY Change	-191.87%	228.01%	-287.83%
FINANCING ACTIVITIES
Cash Dividend Paid
YoY Change
Common Stock Issuance & Retirement, Net
YoY Change
Debt Paid & Issued, Net
YoY Change
Cash From Financing Activities	-228.1M	193.1M	140.8M
YoY Change	-218.13%	-3165.08%	-174.73%
NET CHANGE
Cash From Operating Activities	40.20M	20.60M	25.20M
Cash From Investing Activities	200.1M	-217.8M	-183.7M
Cash From Financing Activities	-228.1M	193.1M	140.8M
Net Change In Cash	12.20M	-4.100M	-17.70M
YoY Change	-397.56%	-92.32%	-69.48%
FREE CASH FLOW
Cash From Operating Activities	$40.20M	$20.60M	$25.20M
Capital Expenditures	-$1.200M	-$4.500M	-$3.500M
Free Cash Flow	$41.40M	$25.10M	$28.70M
YoY Change	64.94%	5.46%	-20.94%

Facts In Submission

Frame	Concept Type	Concept / XBRL Key	Value	Unit
CY2020	dei	Entity Central Index Key EntityCentralIndexKey	0000705432
CY2020	dei	Document Fiscal Year Focus DocumentFiscalYearFocus	2020
CY2020	dei	Document Fiscal Period Focus DocumentFiscalPeriodFocus	FY
CY2020	dei	Amendment Flag AmendmentFlag	false
CY2020	dei	Document Type DocumentType	10-K
CY2020	dei	Document Annual Report DocumentAnnualReport	true
CY2020	dei	Document Period End Date DocumentPeriodEndDate	2020-12-31
CY2020	dei	Current Fiscal Year End Date CurrentFiscalYearEndDate	--12-31
CY2020	dei	Document Transition Report DocumentTransitionReport	false
CY2020	dei	Entity File Number EntityFileNumber	000-12247
CY2020	dei	Entity Registrant Name EntityRegistrantName	SOUTHSIDE BANCSHARES, INC.
CY2020	dei	Entity Incorporation State Country Code EntityIncorporationStateCountryCode	TX
CY2020	dei	Entity Tax Identification Number EntityTaxIdentificationNumber	75-1848732
CY2020	dei	Entity Address Address Line1 EntityAddressAddressLine1	1201 S. Beckham Avenue,
CY2020	dei	Entity Address City Or Town EntityAddressCityOrTown	Tyler,
CY2020	dei	Entity Address State Or Province EntityAddressStateOrProvince	TX
CY2020	dei	Entity Address Postal Zip Code EntityAddressPostalZipCode	75701
CY2020	dei	City Area Code CityAreaCode	903
CY2020	dei	Local Phone Number LocalPhoneNumber	531-7111
CY2020	dei	Security12b Title Security12bTitle	Common Stock, $1.25 par value
CY2020	dei	Trading Symbol TradingSymbol	SBSI
CY2020	dei	Security Exchange Name SecurityExchangeName	NASDAQ
CY2020	dei	Entity Well Known Seasoned Issuer EntityWellKnownSeasonedIssuer	Yes
CY2020	dei	Entity Voluntary Filers EntityVoluntaryFilers	No
CY2020	dei	Entity Current Reporting Status EntityCurrentReportingStatus	Yes
CY2020	dei	Entity Interactive Data Current EntityInteractiveDataCurrent	Yes
CY2020	dei	Entity Filer Category EntityFilerCategory	Large Accelerated Filer
CY2020	dei	Entity Small Business EntitySmallBusiness	false
CY2020	dei	Entity Emerging Growth Company EntityEmergingGrowthCompany	false
CY2020	dei	Icfr Auditor Attestation Flag IcfrAuditorAttestationFlag	true
CY2020	dei	Entity Shell Company EntityShellCompany	false
CY2020Q2	dei	Entity Public Float EntityPublicFloat	860500000	USD
CY2021Q1	dei	Entity Common Stock Shares Outstanding EntityCommonStockSharesOutstanding	32757551	shares
CY2020Q4	us-gaap	Cash And Due From Banks CashAndDueFromBanks	87357000	USD
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CY2020Q4	us-gaap	Interest Bearing Deposits In Banks InterestBearingDepositsInBanks	21051000	USD
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CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	2437513000	USD
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CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	2587305000	USD
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CY2019Q4	us-gaap	Goodwill Goodwill	201116000	USD
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CY2019	sbsi	Fees And Commissions Fiduciary And Trust Activity FeesAndCommissionsFiduciaryAndTrustActivity	6269000	USD
CY2018	sbsi	Fees And Commissions Fiduciary And Trust Activity FeesAndCommissionsFiduciaryAndTrustActivity	6832000	USD
CY2020	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	2554000	USD
CY2019	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	2307000	USD
CY2018	us-gaap	Bank Owned Life Insurance Income BankOwnedLifeInsuranceIncome	2923000	USD
CY2020	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	2271000	USD
CY2019	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	2080000	USD
CY2018	us-gaap	Brokerage Commissions Revenue BrokerageCommissionsRevenue	1987000	USD
CY2020	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	4386000	USD
CY2019	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	4409000	USD
CY2018	us-gaap	Noninterest Income Other Operating Income NoninterestIncomeOtherOperatingIncome	5096000	USD
CY2020	us-gaap	Noninterest Income NoninterestIncome	49732000	USD
CY2019	us-gaap	Noninterest Income NoninterestIncome	42368000	USD
CY2018	us-gaap	Noninterest Income NoninterestIncome	40773000	USD
CY2020	us-gaap	Labor And Related Expense LaborAndRelatedExpense	77225000	USD
CY2019	us-gaap	Labor And Related Expense LaborAndRelatedExpense	73731000	USD
CY2018	us-gaap	Labor And Related Expense LaborAndRelatedExpense	70643000	USD
CY2020	us-gaap	Occupancy Net OccupancyNet	14369000	USD
CY2019	us-gaap	Occupancy Net OccupancyNet	13128000	USD
CY2018	us-gaap	Occupancy Net OccupancyNet	13814000	USD
CY2020	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	0	USD
CY2019	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	0	USD
CY2018	us-gaap	Business Combination Acquisition Related Costs BusinessCombinationAcquisitionRelatedCosts	2413000	USD
CY2020	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2147000	USD
CY2019	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2964000	USD
CY2018	us-gaap	Marketing And Advertising Expense MarketingAndAdvertisingExpense	2894000	USD
CY2020	sbsi	Atm Expense ATMExpense	1018000	USD
CY2019	sbsi	Atm Expense ATMExpense	894000	USD
CY2018	sbsi	Atm Expense ATMExpense	1090000	USD
CY2020	us-gaap	Professional Fees ProfessionalFees	4224000	USD
CY2019	us-gaap	Professional Fees ProfessionalFees	4717000	USD
CY2018	us-gaap	Professional Fees ProfessionalFees	4035000	USD
CY2020	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	4957000	USD
CY2019	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	4537000	USD
CY2018	us-gaap	Information Technology And Data Processing InformationTechnologyAndDataProcessing	3996000	USD
CY2020	us-gaap	Communication Communication	1984000	USD
CY2019	us-gaap	Communication Communication	1941000	USD
CY2018	us-gaap	Communication Communication	1847000	USD
CY2020	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1124000	USD
CY2019	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	859000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Reclassification Adjustments And Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsAndTax	87481000	USD
CY2018	us-gaap	Federal Deposit Insurance Corporation Premium Expense FederalDepositInsuranceCorporationPremiumExpense	1871000	USD
CY2020	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	3617000	USD
CY2019	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	4418000	USD
CY2018	us-gaap	Amortization Of Intangible Assets AmortizationOfIntangibleAssets	5213000	USD
CY2020	us-gaap	Other Noninterest Expense OtherNoninterestExpense	12642000	USD
CY2019	us-gaap	Other Noninterest Expense OtherNoninterestExpense	12108000	USD
CY2018	us-gaap	Other Noninterest Expense OtherNoninterestExpense	12283000	USD
CY2020	us-gaap	Noninterest Expense NoninterestExpense	123307000	USD
CY2019	us-gaap	Noninterest Expense NoninterestExpense	119297000	USD
CY2018	us-gaap	Noninterest Expense NoninterestExpense	120099000	USD
CY2020	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	93489000	USD
CY2019	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	87775000	USD
CY2018	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	84301000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	11336000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13221000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	10163000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Reclassification Adjustments And Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsAndTax	-34238000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	82153000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	74554000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	74138000	USD
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.47
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.21
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.12
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.47
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.20
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.11
CY2020	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.30
CY2019	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.26
CY2018	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.20
CY2020	us-gaap	Net Income Loss NetIncomeLoss	82153000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	74554000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	74138000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Available For Sale Securities Adjustment Before Reclassification Adjustments And Tax OtherComprehensiveIncomeLossAvailableForSaleSecuritiesAdjustmentBeforeReclassificationAdjustmentsAndTax	105845000	USD
CY2020	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Due To Transition Before Adjustment And Tax OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossDueToTransitionBeforeAdjustmentAndTax	0	USD
CY2019	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Due To Transition Before Adjustment And Tax OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossDueToTransitionBeforeAdjustmentAndTax	0	USD
CY2018	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Due To Transition Before Adjustment And Tax OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossDueToTransitionBeforeAdjustmentAndTax	11881000	USD
CY2020	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Before Adjustment And Tax1 OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossBeforeAdjustmentAndTax1	0	USD
CY2019	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Before Adjustment And Tax1 OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossBeforeAdjustmentAndTax1	0	USD
CY2018	sbsi	Oci Debt Securities Available For Sale Transfer From Held To Maturity Gain Loss Before Adjustment And Tax1 OCIDebtSecuritiesAvailableForSaleTransferFromHeldToMaturityGainLossBeforeAdjustmentAndTax1	401000	USD
CY2020	sbsi	Amortizationof Unrealized Gains Losseson Securities Transferred Between Availablefor Sale And Heldto Maturity Debt Securities Before Tax AmortizationofUnrealizedGainsLossesonSecuritiesTransferredBetweenAvailableforSaleAndHeldtoMaturityDebtSecuritiesBeforeTax	-1197000	USD
CY2019	sbsi	Amortizationof Unrealized Gains Losseson Securities Transferred Between Availablefor Sale And Heldto Maturity Debt Securities Before Tax AmortizationofUnrealizedGainsLossesonSecuritiesTransferredBetweenAvailableforSaleAndHeldtoMaturityDebtSecuritiesBeforeTax	-816000	USD
CY2018	sbsi	Amortizationof Unrealized Gains Losseson Securities Transferred Between Availablefor Sale And Heldto Maturity Debt Securities Before Tax AmortizationofUnrealizedGainsLossesonSecuritiesTransferredBetweenAvailableforSaleAndHeldtoMaturityDebtSecuritiesBeforeTax	-1244000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	8257000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	756000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci For Sale Of Securities Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIForSaleOfSecuritiesBeforeTax	-1839000	USD
CY2020	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	-23462000	USD
CY2019	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	-9118000	USD
CY2018	us-gaap	Other Comprehensive Income Unrealized Gain Loss On Derivatives Arising During Period Before Tax OtherComprehensiveIncomeUnrealizedGainLossOnDerivativesArisingDuringPeriodBeforeTax	2351000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	-3945000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	2043000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Reclassification Adjustment From Aoci On Derivatives Before Tax OtherComprehensiveIncomeLossReclassificationAdjustmentFromAOCIOnDerivativesBeforeTax	1406000	USD
CY2020	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Gain Lossand Prior Service Cost Credit Reclassification Adjustmentfrom Aoc Ibefore Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossandPriorServiceCostCreditReclassificationAdjustmentfromAOCIbeforeTax	3028000	USD
CY2019	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Gain Lossand Prior Service Cost Credit Reclassification Adjustmentfrom Aoc Ibefore Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossandPriorServiceCostCreditReclassificationAdjustmentfromAOCIbeforeTax	2378000	USD
CY2018	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Gain Lossand Prior Service Cost Credit Reclassification Adjustmentfrom Aoc Ibefore Tax OtherComprehensiveIncomeLossDefinedBenefitPlanGainLossandPriorServiceCostCreditReclassificationAdjustmentfromAOCIbeforeTax	2182000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	215000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	0	USD
CY2018	us-gaap	Other Comprehensive Income Loss Finalization Of Pension And Non Pension Postretirement Plan Valuation Before Tax OtherComprehensiveIncomeLossFinalizationOfPensionAndNonPensionPostretirementPlanValuationBeforeTax	0	USD
CY2020	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Prior Service Cost Credit Plan Amendment Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanPriorServiceCostCreditPlanAmendmentBeforeTax	163000	USD
CY2019	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Prior Service Cost Credit Plan Amendment Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanPriorServiceCostCreditPlanAmendmentBeforeTax	0	USD
CY2018	sbsi	Other Comprehensive Income Loss Defined Benefit Plan Prior Service Cost Credit Plan Amendment Before Tax OtherComprehensiveIncomeLossDefinedBenefitPlanPriorServiceCostCreditPlanAmendmentBeforeTax	0	USD
CY2020	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-593000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-9816000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Pension And Other Postretirement Benefit Plans Net Unamortized Gain Loss Arising During Period Before Tax OtherComprehensiveIncomeLossPensionAndOtherPostretirementBenefitPlansNetUnamortizedGainLossArisingDuringPeriodBeforeTax	-1994000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	82081000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	68942000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Before Tax OtherComprehensiveIncomeLossBeforeTax	-17740000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	17237000	USD
CY2018	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	60123000	USD
CY2017Q4	us-gaap	Stockholders Equity StockholdersEquity	754140000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	74138000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	14478000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Tax OtherComprehensiveIncomeLossTax	-3725000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	64844000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	54464000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-14015000	USD
CY2020	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	146997000	USD
CY2019	us-gaap	Comprehensive Income Net Of Tax Including Portion Attributable To Noncontrolling Interest ComprehensiveIncomeNetOfTaxIncludingPortionAttributableToNoncontrollingInterest	129018000	USD
CY2018	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	-14015000	USD
CY2018	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	42872	shares
CY2018	us-gaap	Stock Issued During Period Value Dividend Reinvestment Plan StockIssuedDuringPeriodValueDividendReinvestmentPlan	1478000	USD
CY2018	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	1459148	shares
CY2018	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	47193000	USD
CY2018	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	2317000	USD
CY2018	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	140692	shares
CY2018	us-gaap	Stock Issued During Period Value Share Based Compensation StockIssuedDuringPeriodValueShareBasedCompensation	2405000	USD
CY2018	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.20
CY2018	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	41979000	USD
CY2018Q4	us-gaap	Stockholders Equity StockholdersEquity	731291000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	74554000	USD
CY2019	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	54464000	USD
CY2019	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	42438	shares
CY2019	us-gaap	Stock Issued During Period Value Dividend Reinvestment Plan StockIssuedDuringPeriodValueDividendReinvestmentPlan	1445000	USD
CY2019	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	66467	shares
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	2181000	USD
CY2019	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	2388000	USD
CY2019	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	122537	shares
CY2019	us-gaap	Stock Issued During Period Value Share Based Compensation StockIssuedDuringPeriodValueShareBasedCompensation	1592000	USD
CY2019	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.26
CY2019	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	42521000	USD
CY2019Q4	us-gaap	Stockholders Equity StockholdersEquity	804580000	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	82153000	USD
CY2020	us-gaap	Other Comprehensive Income Loss Net Of Tax OtherComprehensiveIncomeLossNetOfTax	64844000	USD
CY2020	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	47157	shares
CY2020	us-gaap	Stock Issued During Period Value Dividend Reinvestment Plan StockIssuedDuringPeriodValueDividendReinvestmentPlan	1424000	USD
CY2020	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	1035901	shares
CY2020	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	30989000	USD
CY2020	us-gaap	Adjustments To Additional Paid In Capital Sharebased Compensation Requisite Service Period Recognition Value AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue	3020000	USD
CY2020	us-gaap	Stock Issued During Period Shares Share Based Compensation StockIssuedDuringPeriodSharesShareBasedCompensation	116661	shares
CY2020	us-gaap	Stock Issued During Period Value Share Based Compensation StockIssuedDuringPeriodValueShareBasedCompensation	1299000	USD
CY2020	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.30
CY2020	us-gaap	Dividends Common Stock Cash DividendsCommonStockCash	43204000	USD
CY2020Q4	us-gaap	Stockholders Equity StockholdersEquity	875297000	USD
CY2020	us-gaap	Profit Loss ProfitLoss	82153000	USD
CY2019	us-gaap	Profit Loss ProfitLoss	74554000	USD
CY2018	us-gaap	Profit Loss ProfitLoss	74138000	USD
CY2020	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	12084000	USD
CY2019	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	12111000	USD
CY2018	us-gaap	Depreciation Depletion And Amortization DepreciationDepletionAndAmortization	14045000	USD
CY2020	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-24291000	USD
CY2019	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-13874000	USD
CY2018	us-gaap	Accretion Amortization Of Discounts And Premiums Investments AccretionAmortizationOfDiscountsAndPremiumsInvestments	-13675000	USD
CY2020	us-gaap	Investment Income Net Amortization Of Discount And Premium InvestmentIncomeNetAmortizationOfDiscountAndPremium	1107000	USD
CY2019	us-gaap	Investment Income Net Amortization Of Discount And Premium InvestmentIncomeNetAmortizationOfDiscountAndPremium	1211000	USD
CY2018	us-gaap	Investment Income Net Amortization Of Discount And Premium InvestmentIncomeNetAmortizationOfDiscountAndPremium	2333000	USD
CY2020	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	20201000	USD
CY2019	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	5101000	USD
CY2018	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	8437000	USD
CY2020	us-gaap	Share Based Compensation ShareBasedCompensation	3020000	USD
CY2019	us-gaap	Share Based Compensation ShareBasedCompensation	2388000	USD
CY2018	us-gaap	Share Based Compensation ShareBasedCompensation	2317000	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-4430000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	122000	USD
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	6154000	USD
CY2020	us-gaap	Availableforsale Securities Gross Realized Gain Loss Excluding Other Than Temporary Impairments AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments	8257000	USD
CY2019	us-gaap	Availableforsale Securities Gross Realized Gain Loss Excluding Other Than Temporary Impairments AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments	756000	USD
CY2018	us-gaap	Availableforsale Securities Gross Realized Gain Loss Excluding Other Than Temporary Impairments AvailableforsaleSecuritiesGrossRealizedGainLossExcludingOtherThanTemporaryImpairments	-1839000	USD
CY2020	us-gaap	Gain Loss On Disposition Of Assets GainLossOnDispositionOfAssets	-877000	USD
CY2019	us-gaap	Gain Loss On Disposition Of Assets GainLossOnDispositionOfAssets	-592000	USD
CY2018	us-gaap	Gain Loss On Disposition Of Assets GainLossOnDispositionOfAssets	-768000	USD
CY2020	us-gaap	Proceeds From Sale Of Mortgage Loans Held For Sale ProceedsFromSaleOfMortgageLoansHeldForSale	74814000	USD
CY2019	us-gaap	Proceeds From Sale Of Mortgage Loans Held For Sale ProceedsFromSaleOfMortgageLoansHeldForSale	22041000	USD
CY2018	us-gaap	Proceeds From Sale Of Mortgage Loans Held For Sale ProceedsFromSaleOfMortgageLoansHeldForSale	24092000	USD
CY2020	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	78126000	USD
CY2019	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	21823000	USD
CY2018	us-gaap	Payments For Origination And Purchases Of Loans Held For Sale PaymentsForOriginationAndPurchasesOfLoansHeldForSale	22692000	USD
CY2020	us-gaap	Gains Losses On Sales Of Other Real Estate GainsLossesOnSalesOfOtherRealEstate	-151000	USD
CY2019	us-gaap	Gains Losses On Sales Of Other Real Estate GainsLossesOnSalesOfOtherRealEstate	100000	USD
CY2018	us-gaap	Gains Losses On Sales Of Other Real Estate GainsLossesOnSalesOfOtherRealEstate	-433000	USD
CY2020	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Curtailments DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments	-163000	USD
CY2019	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Curtailments DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments	0	USD
CY2018	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Curtailments DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments	0	USD
CY2020	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	215000	USD
CY2019	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	0	USD
CY2018	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Settlements1 DefinedBenefitPlanRecognizedNetGainLossDueToSettlements1	0	USD
CY2020	us-gaap	Loans And Leases Receivable Gain Loss On Sales Net LoansAndLeasesReceivableGainLossOnSalesNet	0	USD
CY2019	us-gaap	Loans And Leases Receivable Gain Loss On Sales Net LoansAndLeasesReceivableGainLossOnSalesNet	0	USD
CY2018	us-gaap	Loans And Leases Receivable Gain Loss On Sales Net LoansAndLeasesReceivableGainLossOnSalesNet	124000	USD
CY2020	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	10256000	USD
CY2019	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	1165000	USD
CY2018	us-gaap	Increase Decrease In Accrued Interest Receivable Net IncreaseDecreaseInAccruedInterestReceivableNet	-1204000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	6445000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	12275000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Assets IncreaseDecreaseInOtherOperatingAssets	2166000	USD
CY2020	us-gaap	Increase Decrease In Interest Payable Net IncreaseDecreaseInInterestPayableNet	-3234000	USD
CY2019	us-gaap	Increase Decrease In Interest Payable Net IncreaseDecreaseInInterestPayableNet	530000	USD
CY2018	us-gaap	Increase Decrease In Interest Payable Net IncreaseDecreaseInInterestPayableNet	1257000	USD
CY2020	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	90520000	USD
CY2019	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	80606000	USD
CY2018	us-gaap	Net Cash Provided By Used In Operating Activities NetCashProvidedByUsedInOperatingActivities	122402000	USD
CY2020	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-15594000	USD
CY2019	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	-13377000	USD
CY2018	us-gaap	Increase Decrease In Other Operating Liabilities IncreaseDecreaseInOtherOperatingLiabilities	1358000	USD
CY2020	us-gaap	Payments To Acquire Available For Sale Securities PaymentsToAcquireAvailableForSaleSecurities	916873000	USD
CY2019	us-gaap	Payments To Acquire Available For Sale Securities PaymentsToAcquireAvailableForSaleSecurities	1253139000	USD
CY2018	us-gaap	Payments To Acquire Available For Sale Securities PaymentsToAcquireAvailableForSaleSecurities	306867000	USD
CY2020	us-gaap	Proceeds From Sale Of Available For Sale Securities ProceedsFromSaleOfAvailableForSaleSecurities	316043000	USD
CY2019	us-gaap	Proceeds From Sale Of Available For Sale Securities ProceedsFromSaleOfAvailableForSaleSecurities	751116000	USD
CY2018	us-gaap	Proceeds From Sale Of Available For Sale Securities ProceedsFromSaleOfAvailableForSaleSecurities	428518000	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	437098000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	201529000	USD
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Available For Sale Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfAvailableForSaleSecurities	137883000	USD
CY2020	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	26044000	USD
CY2019	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	27833000	USD
CY2018	us-gaap	Proceeds From Maturities Prepayments And Calls Of Held To Maturity Securities ProceedsFromMaturitiesPrepaymentsAndCallsOfHeldToMaturitySecurities	3064000	USD
CY2020	us-gaap	Proceeds From Sale Of Federal Reserve Stock ProceedsFromSaleOfFederalReserveStock	31000000	USD
CY2019	us-gaap	Proceeds From Sale Of Federal Reserve Stock ProceedsFromSaleOfFederalReserveStock	8788000	USD
CY2018	us-gaap	Proceeds From Sale Of Federal Reserve Stock ProceedsFromSaleOfFederalReserveStock	24360000	USD
CY2020	us-gaap	Payments To Acquire Federal Reserve Stock PaymentsToAcquireFederalReserveStock	5689000	USD
CY2019	us-gaap	Payments To Acquire Federal Reserve Stock PaymentsToAcquireFederalReserveStock	26483000	USD
CY2018	us-gaap	Payments To Acquire Federal Reserve Stock PaymentsToAcquireFederalReserveStock	1518000	USD
CY2020	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	90206000	USD
CY2019	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	262137000	USD
CY2018	us-gaap	Payments For Proceeds From Loans And Leases PaymentsForProceedsFromLoansAndLeases	24491000	USD
CY2020	us-gaap	Proceeds From Sale Of Loans Receivable ProceedsFromSaleOfLoansReceivable	0	USD
CY2019	us-gaap	Proceeds From Sale Of Loans Receivable ProceedsFromSaleOfLoansReceivable	0	USD
CY2018	us-gaap	Proceeds From Sale Of Loans Receivable ProceedsFromSaleOfLoansReceivable	4300000	USD
CY2020	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	11435000	USD
CY2019	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	15883000	USD
CY2018	us-gaap	Payments To Acquire Property Plant And Equipment PaymentsToAcquirePropertyPlantAndEquipment	13444000	USD
CY2020	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	12500000	USD
CY2019	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	0	USD
CY2018	us-gaap	Payments For Proceeds From Life Insurance Policies PaymentsForProceedsFromLifeInsurancePolicies	-5956000	USD
CY2020	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	1846000	USD
CY2019	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	96000	USD
CY2018	us-gaap	Proceeds From Sale Of Property Plant And Equipment ProceedsFromSaleOfPropertyPlantAndEquipment	1943000	USD
CY2020	us-gaap	Proceeds From Sale Of Wholly Owned Real Estate And Real Estate Acquired In Settlement Of Loans ProceedsFromSaleOfWhollyOwnedRealEstateAndRealEstateAcquiredInSettlementOfLoans	766000	USD
CY2019	us-gaap	Proceeds From Sale Of Wholly Owned Real Estate And Real Estate Acquired In Settlement Of Loans ProceedsFromSaleOfWhollyOwnedRealEstateAndRealEstateAcquiredInSettlementOfLoans	1122000	USD
CY2018	us-gaap	Proceeds From Sale Of Wholly Owned Real Estate And Real Estate Acquired In Settlement Of Loans ProceedsFromSaleOfWhollyOwnedRealEstateAndRealEstateAcquiredInSettlementOfLoans	1717000	USD
CY2020	us-gaap	Proceeds From Sale Of Foreclosed Assets ProceedsFromSaleOfForeclosedAssets	171000	USD
CY2019	us-gaap	Proceeds From Sale Of Foreclosed Assets ProceedsFromSaleOfForeclosedAssets	328000	USD
CY2018	us-gaap	Proceeds From Sale Of Foreclosed Assets ProceedsFromSaleOfForeclosedAssets	483000	USD
CY2020	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-223735000	USD
CY2019	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	-566830000	USD
CY2018	us-gaap	Net Cash Provided By Used In Investing Activities NetCashProvidedByUsedInInvestingActivities	261904000	USD
CY2020	us-gaap	Net Change Interest And Noninterest Bearing Deposits Domestic NetChangeInterestAndNoninterestBearingDepositsDomestic	249321000	USD
CY2019	us-gaap	Net Change Interest And Noninterest Bearing Deposits Domestic NetChangeInterestAndNoninterestBearingDepositsDomestic	272638000	USD
CY2018	us-gaap	Net Change Interest And Noninterest Bearing Deposits Domestic NetChangeInterestAndNoninterestBearingDepositsDomestic	-106014000	USD
CY2020	us-gaap	Increase Decrease In Federal Funds Purchased And Securities Sold Under Agreements To Repurchase Net IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet	-5186000	USD
CY2019	us-gaap	Increase Decrease In Federal Funds Purchased And Securities Sold Under Agreements To Repurchase Net IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet	-8452000	USD
CY2018	us-gaap	Increase Decrease In Federal Funds Purchased And Securities Sold Under Agreements To Repurchase Net IncreaseDecreaseInFederalFundsPurchasedAndSecuritiesSoldUnderAgreementsToRepurchaseNet	27312000	USD
CY2020	us-gaap	Proceeds From Federal Home Loan Bank Borrowings ProceedsFromFederalHomeLoanBankBorrowings	21797280000	USD
CY2019	us-gaap	Proceeds From Federal Home Loan Bank Borrowings ProceedsFromFederalHomeLoanBankBorrowings	6914800000	USD
CY2018	us-gaap	Proceeds From Federal Home Loan Bank Borrowings ProceedsFromFederalHomeLoanBankBorrowings	4201500000	USD
CY2020	us-gaap	Repayments Of Federal Home Loan Bank Borrowings RepaymentsOfFederalHomeLoanBankBorrowings	21937497000	USD
CY2019	us-gaap	Repayments Of Federal Home Loan Bank Borrowings RepaymentsOfFederalHomeLoanBankBorrowings	6661119000	USD
CY2018	us-gaap	Repayments Of Federal Home Loan Bank Borrowings RepaymentsOfFederalHomeLoanBankBorrowings	4499788000	USD
CY2020	us-gaap	Proceeds From Issuance Of Subordinated Long Term Debt ProceedsFromIssuanceOfSubordinatedLongTermDebt	98478000	USD
CY2019	us-gaap	Proceeds From Issuance Of Subordinated Long Term Debt ProceedsFromIssuanceOfSubordinatedLongTermDebt	0	USD
CY2018	us-gaap	Proceeds From Issuance Of Subordinated Long Term Debt ProceedsFromIssuanceOfSubordinatedLongTermDebt	0	USD
CY2020	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	1692000	USD
CY2019	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	1986000	USD
CY2018	us-gaap	Proceeds From Stock Options Exercised ProceedsFromStockOptionsExercised	2653000	USD
CY2020	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	393000	USD
CY2019	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	394000	USD
CY2018	us-gaap	Payments Related To Tax Withholding For Share Based Compensation PaymentsRelatedToTaxWithholdingForShareBasedCompensation	248000	USD
CY2020	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	30989000	USD
CY2019	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	2181000	USD
CY2018	us-gaap	Payments For Repurchase Of Common Stock PaymentsForRepurchaseOfCommonStock	47193000	USD
CY2020	us-gaap	Proceeds From Issuance Of Common Stock Dividend Reinvestment Plan ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan	1424000	USD
CY2019	us-gaap	Proceeds From Issuance Of Common Stock Dividend Reinvestment Plan ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan	1445000	USD
CY2018	us-gaap	Proceeds From Issuance Of Common Stock Dividend Reinvestment Plan ProceedsFromIssuanceOfCommonStockDividendReinvestmentPlan	1478000	USD
CY2020	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	43204000	USD
CY2019	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	42521000	USD
CY2018	us-gaap	Payments Of Dividends Common Stock PaymentsOfDividendsCommonStock	41979000	USD
CY2020	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	130926000	USD
CY2019	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	476202000	USD
CY2018	us-gaap	Net Cash Provided By Used In Financing Activities NetCashProvidedByUsedInFinancingActivities	-462279000	USD
CY2020	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-2289000	USD
CY2019	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-10022000	USD
CY2018	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents Period Increase Decrease Including Exchange Rate Effect CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect	-77973000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	110697000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	120719000	USD
CY2017Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	198692000	USD
CY2020Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	108408000	USD
CY2019Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	110697000	USD
CY2018Q4	us-gaap	Cash Cash Equivalents Restricted Cash And Restricted Cash Equivalents CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents	120719000	USD
CY2020	us-gaap	Interest Paid Net InterestPaidNet	47201000	USD
CY2019	us-gaap	Interest Paid Net InterestPaidNet	70452000	USD
CY2018	us-gaap	Interest Paid Net InterestPaidNet	55844000	USD
CY2020	us-gaap	Income Taxes Paid IncomeTaxesPaid	12000000	USD
CY2019	us-gaap	Income Taxes Paid IncomeTaxesPaid	10500000	USD
CY2018	us-gaap	Income Taxes Paid IncomeTaxesPaid	2000000	USD
CY2020	sbsi	Loans Transferred To Other Repossessed Assets And Real Estate Through Foreclosure LoansTransferredToOtherRepossessedAssetsAndRealEstateThroughForeclosure	749000	USD
CY2019	sbsi	Loans Transferred To Other Repossessed Assets And Real Estate Through Foreclosure LoansTransferredToOtherRepossessedAssetsAndRealEstateThroughForeclosure	649000	USD
CY2018	sbsi	Loans Transferred To Other Repossessed Assets And Real Estate Through Foreclosure LoansTransferredToOtherRepossessedAssetsAndRealEstateThroughForeclosure	2128000	USD
CY2020	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2019	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	0	USD
CY2018	us-gaap	Transfer Of Portfolio Loans And Leases To Held For Sale1 TransferOfPortfolioLoansAndLeasesToHeldForSale1	3984000	USD
CY2020	us-gaap	Debt Securities Held To Maturity Transfer Amount DebtSecuritiesHeldToMaturityTransferAmount	0	USD
CY2019	us-gaap	Debt Securities Held To Maturity Transfer Amount DebtSecuritiesHeldToMaturityTransferAmount	0	USD
CY2018	us-gaap	Debt Securities Held To Maturity Transfer Amount DebtSecuritiesHeldToMaturityTransferAmount	743421000	USD
CY2020Q4	sbsi	Unsettled Trades To Purchase Securities Liability UnsettledTradesToPurchaseSecuritiesLiability	0	USD
CY2019Q4	sbsi	Unsettled Trades To Purchase Securities Liability UnsettledTradesToPurchaseSecuritiesLiability	17538000	USD
CY2018Q4	sbsi	Unsettled Trades To Purchase Securities Liability UnsettledTradesToPurchaseSecuritiesLiability	6378000	USD
CY2020Q4	sbsi	Unsettled Issuancesof Brokered C Ds UnsettledIssuancesofBrokeredCDs	0	USD
CY2019Q4	sbsi	Unsettled Issuancesof Brokered C Ds UnsettledIssuancesofBrokeredCDs	20000000	USD
CY2018Q4	sbsi	Unsettled Issuancesof Brokered C Ds UnsettledIssuancesofBrokeredCDs	15236000	USD
CY2020Q4	sbsi	Numberofbankingcenters Numberofbankingcenters	57	banking_offices
CY2020Q4	sbsi	Numberofbankingcentersingrocerystores Numberofbankingcentersingrocerystores	15	banking_offices
CY2020Q1	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	24797000	USD
CY2020Q1	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1455000	USD
CY2020	us-gaap	Use Of Estimates UseOfEstimates	Use of Estimates. In preparing consolidated financial statements in conformity with GAAP, management is required to make estimates and assumptions that affect the reported amounts of assets and liabilities as of the date of the balance sheet and reported amounts of revenues and expenses during the reporting period. These estimates are subjective in nature and involve matters of judgment. Actual results could differ from these estimates. Material estimates that are particularly susceptible to significant change in the near term relate to the determination of the allowance for credit losses, assumptions used in the defined benefit plan and the fair values of financial instruments. The status of contingencies are particularly subject to change and significant assumptions used in periodic evaluation of securities for other-than-temporary impairment.
CY2020	us-gaap	Number Of Reportable Segments NumberOfReportableSegments	1	segment
CY2020Q4	us-gaap	Cash Reserve Deposit Required And Made CashReserveDepositRequiredAndMade	0	USD
CY2019Q4	us-gaap	Cash Reserve Deposit Required And Made CashReserveDepositRequiredAndMade	33800000	USD
CY2020	us-gaap	Revenue Recognition Interest RevenueRecognitionInterest	<span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%;text-decoration:underline">Accrued Interest</span><span style="color:#000000;font-family:'Times New Roman',sans-serif;font-size:10pt;font-weight:400;line-height:120%">. Accrued interest for our loans and debt securities, included in interest receivable on our consolidated balance sheets, is excluded from the estimate of allowance for credit losses.</span>
CY2020Q4	us-gaap	Financing Receivable Threshold Period Past Due FinancingReceivableThresholdPeriodPastDue	P90D
CY2020Q4	us-gaap	Financing Receivable Threshold Period Past Due Writeoff FinancingReceivableThresholdPeriodPastDueWriteoff	P120D
CY2020Q4	us-gaap	Debt Securities Held To Maturity Allowance For Credit Loss DebtSecuritiesHeldToMaturityAllowanceForCreditLoss	0	USD
CY2019	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2020	us-gaap	Goodwill Impairment Loss GoodwillImpairmentLoss	0	USD
CY2020	sbsi	Goodwill Impairmentlosscumulative GoodwillImpairmentlosscumulative	0	USD
CY2019	sbsi	Goodwill Impairmentlosscumulative GoodwillImpairmentlosscumulative	0	USD
CY2020	us-gaap	Net Income Loss NetIncomeLoss	82153000	USD
CY2019	us-gaap	Net Income Loss NetIncomeLoss	74554000	USD
CY2018	us-gaap	Net Income Loss NetIncomeLoss	74138000	USD
CY2020	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	33201000	shares
CY2019	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	33747000	shares
CY2018	us-gaap	Weighted Average Number Of Shares Outstanding Basic WeightedAverageNumberOfSharesOutstandingBasic	34951000	shares
CY2020	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	80000	shares
CY2019	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	148000	shares
CY2018	us-gaap	Incremental Common Shares Attributable To Share Based Payment Arrangements IncrementalCommonSharesAttributableToShareBasedPaymentArrangements	165000	shares
CY2020	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	33281000	shares
CY2019	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	33895000	shares
CY2018	us-gaap	Weighted Average Number Of Diluted Shares Outstanding WeightedAverageNumberOfDilutedSharesOutstanding	35116000	shares
CY2020	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.47
CY2019	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.21
CY2018	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	2.12
CY2020	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.47
CY2019	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.20
CY2018	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	2.11
CY2020	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	808000	shares
CY2019	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	521000	shares
CY2018	us-gaap	Antidilutive Securities Excluded From Computation Of Earnings Per Share Amount AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount	356000	shares
CY2020	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	69000	USD
CY2019	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-313000	USD
CY2018	us-gaap	Reclassification From Accumulated Other Comprehensive Income Current Period Net Of Tax ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax	-3048000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	2437513000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	150074000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	282000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	2587305000	USD
CY2020Q4	sbsi	Debt Securities Heldto Maturity Netof Allowancefor Credit Losses DebtSecuritiesHeldtoMaturityNetofAllowanceforCreditLosses	108998000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	9200000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	0	USD
CY2020Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	118198000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	2306741000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Gain Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	54426000	USD
CY2019Q4	us-gaap	Available For Sale Debt Securities Accumulated Gross Unrealized Loss Before Tax AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	2570000	USD
CY2019Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	2358597000	USD
CY2019Q4	us-gaap	Held To Maturity Securities HeldToMaturitySecurities	134863000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Gain HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingGain	4238000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Accumulated Unrecognized Holding Loss HeldToMaturitySecuritiesAccumulatedUnrecognizedHoldingLoss	222000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	138879000	USD
CY2020Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	1560000000	USD
CY2019Q4	us-gaap	Pledged Financial Instruments Not Separately Reported Securities Pledged PledgedFinancialInstrumentsNotSeparatelyReportedSecuritiesPledged	1120000000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	39898000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	282000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	0	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	0	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	39898000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	282000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months	273963000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	2282000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger	30697000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	288000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position DebtSecuritiesAvailableForSaleUnrealizedLossPosition	304660000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Unrealized Loss Position Accumulated Loss DebtSecuritiesAvailableForSaleUnrealizedLossPositionAccumulatedLoss	2570000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue	13053000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Less Than12 Months Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss	76000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Twelve Months Or Longer Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue	4092000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position12 Months Or Longer Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss	146000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Fair Value HeldToMaturitySecuritiesContinuousUnrealizedLossPositionFairValue	17145000	USD
CY2019Q4	us-gaap	Held To Maturity Securities Continuous Unrealized Loss Position Accumulated Loss HeldToMaturitySecuritiesContinuousUnrealizedLossPositionAccumulatedLoss	222000	USD
CY2020	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss Period Increase Decrease DebtSecuritiesAvailableForSaleAllowanceForCreditLossPeriodIncreaseDecrease	0	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Allowance For Credit Loss DebtSecuritiesAvailableForSaleAllowanceForCreditLoss	0	USD
CY2019	us-gaap	Other Than Temporary Impairment Losses Investments Portion Recognized In Earnings Net Availableforsale Securities OtherThanTemporaryImpairmentLossesInvestmentsPortionRecognizedInEarningsNetAvailableforsaleSecurities	0	USD
CY2020	us-gaap	Debt Securities Held To Maturity Credit Loss Expense Reversal DebtSecuritiesHeldToMaturityCreditLossExpenseReversal	0	USD
CY2020Q4	sbsi	Transferred Securities Unrealized Loss Before Tax TransferredSecuritiesUnrealizedLossBeforeTax	2900000	USD
CY2020Q4	sbsi	Securities Transferred Unrealized Loss Net Of Tax SecuritiesTransferredUnrealizedLossNetOfTax	2300000	USD
CY2019Q4	sbsi	Transferred Securities Unrealized Loss Before Tax TransferredSecuritiesUnrealizedLossBeforeTax	3700000	USD
CY2019Q4	sbsi	Securities Transferred Unrealized Loss Net Of Tax SecuritiesTransferredUnrealizedLossNetOfTax	2900000	USD
CY2020	sbsi	Securities Transferred From Available For Sale To Held To Maturity SecuritiesTransferredFromAvailableForSaleToHeldToMaturity	0	USD
CY2019	sbsi	Securities Transferred From Available For Sale To Held To Maturity SecuritiesTransferredFromAvailableForSaleToHeldToMaturity	0	USD
CY2020Q4	us-gaap	Debt Securities Held To Maturity Past Due DebtSecuritiesHeldToMaturityPastDue	0	USD
CY2020Q4	us-gaap	Debt Securities Held To Maturity Nonaccrual DebtSecuritiesHeldToMaturityNonaccrual	0	USD
CY2020	us-gaap	Interest Income Securities Us Treasury InterestIncomeSecuritiesUSTreasury	0	USD
CY2019	us-gaap	Interest Income Securities Us Treasury InterestIncomeSecuritiesUSTreasury	0	USD
CY2018	us-gaap	Interest Income Securities Us Treasury InterestIncomeSecuritiesUSTreasury	218000	USD
CY2020	us-gaap	Interest Income Securities Other Us Government InterestIncomeSecuritiesOtherUSGovernment	0	USD
CY2019	us-gaap	Interest Income Securities Other Us Government InterestIncomeSecuritiesOtherUSGovernment	0	USD
CY2018	us-gaap	Interest Income Securities Other Us Government InterestIncomeSecuritiesOtherUSGovernment	89000	USD
CY2020	us-gaap	Interest Income Securities State And Municipal InterestIncomeSecuritiesStateAndMunicipal	36393000	USD
CY2019	us-gaap	Interest Income Securities State And Municipal InterestIncomeSecuritiesStateAndMunicipal	16885000	USD
CY2018	us-gaap	Interest Income Securities State And Municipal InterestIncomeSecuritiesStateAndMunicipal	24960000	USD
CY2020	sbsi	Interest Income Other Stocks And Bonds InterestIncomeOtherStocksAndBonds	1195000	USD
CY2019	sbsi	Interest Income Other Stocks And Bonds InterestIncomeOtherStocksAndBonds	138000	USD
CY2018	sbsi	Interest Income Other Stocks And Bonds InterestIncomeOtherStocksAndBonds	110000	USD
CY2020	us-gaap	Interest Income Securities Mortgage Backed InterestIncomeSecuritiesMortgageBacked	34319000	USD
CY2019	us-gaap	Interest Income Securities Mortgage Backed InterestIncomeSecuritiesMortgageBacked	50486000	USD
CY2018	us-gaap	Interest Income Securities Mortgage Backed InterestIncomeSecuritiesMortgageBacked	41584000	USD
CY2020	us-gaap	Interest And Other Income InterestAndOtherIncome	71907000	USD
CY2019	us-gaap	Interest And Other Income InterestAndOtherIncome	67509000	USD
CY2018	us-gaap	Interest And Other Income InterestAndOtherIncome	66961000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	8300000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	8400000	USD
CY2020	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	129000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	756000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	5700000	USD
CY2019	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	4900000	USD
CY2018	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	-1800000	USD
CY2018	us-gaap	Debt Securities Available For Sale Realized Loss DebtSecuritiesAvailableForSaleRealizedLoss	3800000	USD
CY2018	us-gaap	Debt Securities Available For Sale Realized Gain DebtSecuritiesAvailableForSaleRealizedGain	2000000.0	USD
CY2020	us-gaap	Proceeds From Sale Of Held To Maturity Securities ProceedsFromSaleOfHeldToMaturitySecurities	0	USD
CY2019	us-gaap	Proceeds From Sale Of Held To Maturity Securities ProceedsFromSaleOfHeldToMaturitySecurities	0	USD
CY2018	us-gaap	Proceeds From Sale Of Held To Maturity Securities ProceedsFromSaleOfHeldToMaturitySecurities	0	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearAmortizedCost	2185000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Within One Year Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithinOneYearFairValue	2223000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsAmortizedCost	32972000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After One Through Five Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	33953000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsAmortizedCost	90751000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Five Through Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	93430000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsAmortizedCost	1426346000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities After Ten Years Fair Value AvailableForSaleSecuritiesDebtMaturitiesAfterTenYearsFairValue	1529243000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date Amortized Cost Basis AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis	1552254000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Single Maturity Date AvailableForSaleSecuritiesDebtMaturitiesSingleMaturityDate	1658849000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Without Single Maturity Date Amortized Cost AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateAmortizedCost	885259000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Maturities Without Single Maturity Date Fair Value AvailableForSaleSecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue	928456000	USD
CY2020Q4	us-gaap	Available For Sale Debt Securities Amortized Cost Basis AvailableForSaleDebtSecuritiesAmortizedCostBasis	2437513000	USD
CY2020Q4	us-gaap	Available For Sale Securities Debt Securities AvailableForSaleSecuritiesDebtSecurities	2587305000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount	120000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Within One Year Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue	121000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsNetCarryingAmount	509000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After One Through Five Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterOneThroughFiveYearsFairValue	516000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsNetCarryingAmount	278000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After Five Through Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterFiveThroughTenYearsFairValue	283000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsNetCarryingAmount	0	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities After Ten Years Fair Value HeldToMaturitySecuritiesDebtMaturitiesAfterTenYearsFairValue	0	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Single Maturity Date Amortized Cost Basis HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateAmortizedCostBasis	907000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Single Maturity Date Fair Value HeldToMaturitySecuritiesDebtMaturitiesSingleMaturityDateFairValue	920000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Without Single Maturity Date Net Carrying Amount HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateNetCarryingAmount	108091000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Debt Maturities Without Single Maturity Date Fair Value HeldToMaturitySecuritiesDebtMaturitiesWithoutSingleMaturityDateFairValue	117278000	USD
CY2020Q4	sbsi	Debt Securities Heldto Maturity Netof Allowancefor Credit Losses DebtSecuritiesHeldtoMaturityNetofAllowanceforCreditLosses	108998000	USD
CY2020Q4	us-gaap	Held To Maturity Securities Fair Value HeldToMaturitySecuritiesFairValue	118198000	USD
CY2020Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	11900000	USD
CY2019Q4	us-gaap	Equity Securities Fv Ni And Without Readily Determinable Fair Value EquitySecuritiesFvNiAndWithoutReadilyDeterminableFairValue	12300000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	24797000	USD
CY2020	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	-427000	USD
CY2019	us-gaap	Unrealized Gain Loss On Investments UnrealizedGainLossOnInvestments	66000	USD
CY2020	us-gaap	Gain Loss On Sale Of Investments GainLossOnSaleOfInvestments	0	USD
CY2019	us-gaap	Gain Loss On Sale Of Investments GainLossOnSaleOfInvestments	0	USD
CY2020	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	-427000	USD
CY2019	us-gaap	Realized Investment Gains Losses RealizedInvestmentGainsLosses	66000	USD
CY2020Q4	sbsi	Other Than Temporarily Impaired Equity Investments OtherThanTemporarilyImpairedEquityInvestments	0	USD
CY2020Q4	sbsi	Fhlb Stock With Other Than Temporary Impairment FHLBStockWithOtherThanTemporaryImpairment	0	USD
CY2020Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3657779000	USD
CY2019Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3568204000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	49006000	USD
CY2020Q4	us-gaap	Notes Receivable Net NotesReceivableNet	3608773000	USD
CY2019Q4	us-gaap	Notes Receivable Net NotesReceivableNet	3543407000	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	32200000	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Related Parties LoansAndLeasesReceivableRelatedParties	33800000	USD
CY2020Q4	sbsi	Loans And Leases Receivable Related Parties As Percent Of Shareholders Equity LoansAndLeasesReceivableRelatedPartiesAsPercentOfShareholdersEquity	0.037	Rate
CY2019Q4	sbsi	Loans And Leases Receivable Related Parties As Percent Of Shareholders Equity LoansAndLeasesReceivableRelatedPartiesAsPercentOfShareholdersEquity	0.042	Rate
CY2020Q4	us-gaap	Financing Receivable Originated In Current Fiscal Year FinancingReceivableOriginatedInCurrentFiscalYear	1030002000	USD
CY2020Q4	us-gaap	Financing Receivable Originated In Fiscal Year Before Latest Fiscal Year FinancingReceivableOriginatedInFiscalYearBeforeLatestFiscalYear	779358000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Two Years Before Latest Fiscal Year FinancingReceivableOriginatedTwoYearsBeforeLatestFiscalYear	370505000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Three Years Before Latest Fiscal Year FinancingReceivableOriginatedThreeYearsBeforeLatestFiscalYear	389723000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Four Years Before Latest Fiscal Year FinancingReceivableOriginatedFourYearsBeforeLatestFiscalYear	199634000	USD
CY2020Q4	us-gaap	Financing Receivable Originated Five Or More Years Before Latest Fiscal Year FinancingReceivableOriginatedFiveOrMoreYearsBeforeLatestFiscalYear	627713000	USD
CY2020Q4	us-gaap	Financing Receivable Revolving FinancingReceivableRevolving	260844000	USD
CY2020Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3657779000	USD
CY2020Q4	us-gaap	Financing Receivable Recorded Investment Past Due FinancingReceivableRecordedInvestmentPastDue	21587000	USD
CY2019Q4	us-gaap	Financing Receivable Recorded Investment Past Due FinancingReceivableRecordedInvestmentPastDue	19203000	USD
CY2019Q4	us-gaap	Financing Receivable Recorded Investment Current FinancingReceivableRecordedInvestmentCurrent	3549001000	USD
CY2020Q4	us-gaap	Financing Receivable Recorded Investment Current FinancingReceivableRecordedInvestmentCurrent	3636192000	USD
CY2020Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3657779000	USD
CY2019Q4	us-gaap	Notes Receivable Gross NotesReceivableGross	3568204000	USD
CY2020Q4	sbsi	Restructured Nonaccrual Loans RestructuredNonaccrualLoans	976000	USD
CY2019Q4	sbsi	Restructured Nonaccrual Loans RestructuredNonaccrualLoans	469000	USD
CY2019Q4	sbsi	Purchase Credit Impaired Loans Restructured PurchaseCreditImpairedLoansRestructured	755000	USD
CY2020	sbsi	Financing Receivable Nonaccrual Interest Income Reversal FinancingReceivableNonaccrualInterestIncomeReversal	193000	USD
CY2020Q4	us-gaap	Financing Receivable Nonaccrual No Allowance FinancingReceivableNonaccrualNoAllowance	2200000	USD
CY2020Q4	sbsi	Financing Receivable Collateral Dependent FinancingReceivableCollateralDependent	11500000	USD
CY2020Q4	sbsi	Loansin Processof Foreclosure LoansinProcessofForeclosure	1200000	USD
CY2019Q4	sbsi	Loansin Processof Foreclosure LoansinProcessofForeclosure	992000	USD
CY2020	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	521000	USD
CY2020	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	8	contract
CY2019	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	8955000	USD
CY2019	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	18	contract
CY2018	us-gaap	Financing Receivable Modifications Post Modification Recorded Investment2 FinancingReceivableModificationsPostModificationRecordedInvestment2	11269000	USD
CY2018	us-gaap	Financing Receivable Modifications Number Of Contracts2 FinancingReceivableModificationsNumberOfContracts2	22	contract
CY2018Q4	us-gaap	Loans And Leases Receivable Impaired Commitment To Lend LoansAndLeasesReceivableImpairedCommitmentToLend	0	USD
CY2019Q4	us-gaap	Loans And Leases Receivable Impaired Commitment To Lend LoansAndLeasesReceivableImpairedCommitmentToLend	0	USD
CY2020Q4	us-gaap	Loans And Leases Receivable Impaired Commitment To Lend LoansAndLeasesReceivableImpairedCommitmentToLend	0	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	24797000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	2854000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	1650000	USD
CY2020	us-gaap	Financing Receivable Allowance For Credit Loss Writeoff After Recovery FinancingReceivableAllowanceForCreditLossWriteoffAfterRecovery	1204000	USD
CY2020	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	20110000	USD
CY2020Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	49006000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	27019000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	8933000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	1610000	USD
CY2019	us-gaap	Financing Receivable Allowance For Credit Loss Writeoff After Recovery FinancingReceivableAllowanceForCreditLossWriteoffAfterRecovery	7323000	USD
CY2019	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	5101000	USD
CY2019Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	24797000	USD
CY2017Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	20781000	USD
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Write Offs FinancingReceivableAllowanceForCreditLossesWriteOffs	4246000	USD
CY2018	us-gaap	Financing Receivable Allowance For Credit Losses Recovery FinancingReceivableAllowanceForCreditLossesRecovery	2047000	USD
CY2018	us-gaap	Financing Receivable Allowance For Credit Loss Writeoff After Recovery FinancingReceivableAllowanceForCreditLossWriteoffAfterRecovery	2199000	USD
CY2018	us-gaap	Provision For Loan Losses Expensed ProvisionForLoanLossesExpensed	8437000	USD
CY2018Q4	us-gaap	Financing Receivable Allowance For Credit Losses FinancingReceivableAllowanceForCreditLosses	27019000	USD
CY2020Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	180025000	USD
CY2019Q4	us-gaap	Buildings And Improvements Gross BuildingsAndImprovementsGross	176949000	USD
CY2020Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	39842000	USD
CY2019Q4	us-gaap	Furniture And Fixtures Gross FurnitureAndFixturesGross	44647000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	219867000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Gross PropertyPlantAndEquipmentGross	221596000	USD
CY2020Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	75291000	USD
CY2019Q4	us-gaap	Accumulated Depreciation Depletion And Amortization Property Plant And Equipment AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment	77684000	USD
CY2020Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	144576000	USD
CY2019Q4	us-gaap	Property Plant And Equipment Net PropertyPlantAndEquipmentNet	143912000	USD
CY2020	us-gaap	Accumulated Depreciation Depletion And Amortization Sale Of Property Plant And Equipment1 AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment1	10400000	USD
CY2019	us-gaap	Accumulated Depreciation Depletion And Amortization Sale Of Property Plant And Equipment1 AccumulatedDepreciationDepletionAndAmortizationSaleOfPropertyPlantAndEquipment1	1500000	USD
CY2020	us-gaap	Depreciation Depreciation	8000000.0	USD
CY2019	us-gaap	Depreciation Depreciation	7300000	USD
CY2018	us-gaap	Depreciation Depreciation	8400000	USD
CY2020Q4	us-gaap	Noninterest Bearing Deposit Liabilities Domestic NoninterestBearingDepositLiabilitiesDomestic	1354815000	USD
CY2019Q4	us-gaap	Noninterest Bearing Deposit Liabilities Domestic NoninterestBearingDepositLiabilitiesDomestic	1040112000	USD
CY2020Q4	us-gaap	Interest Bearing Deposit Liabilities Domestic InterestBearingDepositLiabilitiesDomestic	3577507000	USD
CY2019Q4	us-gaap	Interest Bearing Deposit Liabilities Domestic InterestBearingDepositLiabilitiesDomestic	3662657000	USD
CY2020Q4	us-gaap	Deposits Deposits	4932322000	USD
CY2019Q4	us-gaap	Deposits Deposits	4702769000	USD
CY2020	sbsi	Interest Expense Time Deposits250000or More InterestExpenseTimeDeposits250000orMore	7400000	USD
CY2019	sbsi	Interest Expense Time Deposits250000or More InterestExpenseTimeDeposits250000orMore	7600000	USD
CY2018	sbsi	Interest Expense Time Deposits250000or More InterestExpenseTimeDeposits250000orMore	8500000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year One TimeDepositMaturitiesYearOne	651898000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Two TimeDepositMaturitiesYearTwo	88465000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Three TimeDepositMaturitiesYearThree	25784000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Four TimeDepositMaturitiesYearFour	10307000	USD
CY2020Q4	us-gaap	Time Deposit Maturities Year Five TimeDepositMaturitiesYearFive	14525000	USD
CY2020Q4	us-gaap	Time Deposit Maturities After Year Five TimeDepositMaturitiesAfterYearFive	118000	USD
CY2020Q4	us-gaap	Time Deposits TimeDeposits	791097000	USD
CY2020Q4	us-gaap	Related Party Deposit Liabilities RelatedPartyDepositLiabilities	10400000	USD
CY2019Q4	us-gaap	Related Party Deposit Liabilities RelatedPartyDepositLiabilities	9900000	USD
CY2020Q4	us-gaap	Deposit Liabilities Reclassified As Loans Receivable1 DepositLiabilitiesReclassifiedAsLoansReceivable1	933000	USD
CY2019Q4	us-gaap	Deposit Liabilities Reclassified As Loans Receivable1 DepositLiabilitiesReclassifiedAsLoansReceivable1	1700000	USD
CY2020Q4	sbsi	Borrowed Funds Maturities Repaymentsof Principalinthe Next Twelve Months BorrowedFundsMaturitiesRepaymentsofPrincipalintheNextTwelveMonths	851661000	USD
CY2020Q4	sbsi	Borrowed Funds Maturingin Year Two BorrowedFundsMaturinginYearTwo	680000	USD
CY2020Q4	sbsi	Borrowed Funds Maturingin Year Three BorrowedFundsMaturinginYearThree	710000	USD
CY2020Q4	sbsi	Borrowed Funds Maturingin Year Four BorrowedFundsMaturinginYearFour	740000	USD
CY2020Q4	sbsi	Borrowed Funds Maturingin Year Five BorrowedFundsMaturinginYearFive	772000	USD
CY2020Q4	sbsi	Borrowed Funds Maturing After Year Five BorrowedFundsMaturingAfterYearFive	1136000	USD
CY2020Q4	us-gaap	Debt And Capital Lease Obligations DebtAndCapitalLeaseObligations	855699000	USD
CY2020Q4	sbsi	Line Of Credit Facility Number Of Credit Lines Maintained By Company LineOfCreditFacilityNumberOfCreditLinesMaintainedByCompany	3	credit_line
CY2020Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	0	USD
CY2019Q4	us-gaap	Federal Funds Purchased FederalFundsPurchased	0	USD
CY2020Q4	sbsi	Letters Of Credit Fhlb As Collateral LettersOfCreditFhlbAsCollateral	0	USD
CY2020Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	23200000	USD
CY2019Q4	us-gaap	Securities Sold Under Agreements To Repurchase SecuritiesSoldUnderAgreementsToRepurchase	28400000	USD
CY2020	sbsi	Repurchase Agreement Counterparty Maturityof Agreements RepurchaseAgreementCounterpartyMaturityofAgreements	P1Y
CY2020Q4	us-gaap	Federal Home Loan Bank Advances General Debt Obligations Disclosures Amount Of Available Unused Funds FederalHomeLoanBankAdvancesGeneralDebtObligationsDisclosuresAmountOfAvailableUnusedFunds	1150000000	USD
CY2020Q4	us-gaap	Subordinated Debt SubordinatedDebt	197251000	USD
CY2019Q4	us-gaap	Subordinated Debt SubordinatedDebt	98576000	USD
CY2020Q4	us-gaap	Other Long Term Debt OtherLongTermDebt	60255000	USD
CY2019Q4	us-gaap	Other Long Term Debt OtherLongTermDebt	60250000	USD
CY2020Q4	us-gaap	Long Term Debt LongTermDebt	257506000	USD
CY2019Q4	us-gaap	Long Term Debt LongTermDebt	158826000	USD
CY2020	sbsi	Supplemental Unemployment Benefits Disability Related Benefits Automatic Coverage Qualification Minimum Annual Salary Level SupplementalUnemploymentBenefitsDisabilityRelatedBenefitsAutomaticCoverageQualificationMinimumAnnualSalaryLevel	50000	USD
CY2020	sbsi	Health Care Costs HealthCareCosts	7000000.0	USD
CY2019	sbsi	Health Care Costs HealthCareCosts	7900000	USD
CY2018	sbsi	Health Care Costs HealthCareCosts	6500000	USD
CY2020	sbsi	Other Postretirement Benefits Health Insurance Coverage For Employees Retiring Requisite Service Period OtherPostretirementBenefitsHealthInsuranceCoverageForEmployeesRetiringRequisiteServicePeriod	P50Y
CY2018Q4	sbsi	Retireesparticipatinginhealthinsurance Retireesparticipatinginhealthinsurance	1
CY2020Q4	sbsi	Retireesparticipatinginhealthinsurance Retireesparticipatinginhealthinsurance	1
CY2019Q4	sbsi	Retireesparticipatinginhealthinsurance Retireesparticipatinginhealthinsurance	1
CY2020	us-gaap	Employee Stock Ownership Plan Esop Cash Contributions To Esop EmployeeStockOwnershipPlanESOPCashContributionsToESOP	1000000.0	USD
CY2019	us-gaap	Employee Stock Ownership Plan Esop Cash Contributions To Esop EmployeeStockOwnershipPlanESOPCashContributionsToESOP	700000	USD
CY2018	us-gaap	Employee Stock Ownership Plan Esop Cash Contributions To Esop EmployeeStockOwnershipPlanESOPCashContributionsToESOP	700000	USD
CY2020Q4	us-gaap	Employee Stock Ownership Plan Esop Shares In Esop EmployeeStockOwnershipPlanESOPSharesInESOP	323606	shares
CY2019Q4	us-gaap	Employee Stock Ownership Plan Esop Shares In Esop EmployeeStockOwnershipPlanESOPSharesInESOP	283097	shares
CY2020	sbsi	Supplemental Unemployment Benefits Disability Related Benefits Automatic Coverage Qualification Requisite Service Period SupplementalUnemploymentBenefitsDisabilityRelatedBenefitsAutomaticCoverageQualificationRequisiteServicePeriod	P3Y
CY2020	sbsi	Supplemental Unemployment Benefits Disability Related Benefits Maximum Benefit Provided Per Month SupplementalUnemploymentBenefitsDisabilityRelatedBenefitsMaximumBenefitProvidedPerMonth	15000	USD
CY2020	sbsi	Defined Contribution Plan Requisite Service Period DefinedContributionPlanRequisiteServicePeriod	P30D
CY2020	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	1900000	USD
CY2019	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	1600000	USD
CY2018	us-gaap	Defined Contribution Plan Cost Recognized DefinedContributionPlanCostRecognized	1500000	USD
	us-gaap	Defined Benefit Plan Recognized Net Gain Loss Due To Curtailments DefinedBenefitPlanRecognizedNetGainLossDueToCurtailments	-163000	USD
CY2020Q2	us-gaap	Defined Benefit Plan Accumulated Other Comprehensive Income Net Gains Losses After Tax DefinedBenefitPlanAccumulatedOtherComprehensiveIncomeNetGainsLossesAfterTax	-6000000.0	USD
CY2020	sbsi	Adjustment To Pension Liability AdjustmentToPensionLiability	-2800000	USD
CY2020Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Outstanding Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions	1002039	shares
CY2020Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Exercise Price Beginning Balance1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1	32.17
CY2020	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Outstanding Options Weighted Average Remaining Contractual Term2 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2	P6Y7M9D
CY2020Q4	us-gaap	Share Based Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Number Of Exercisable Options ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions	633459	shares
CY2020Q4	us-gaap	Sharebased Compensation Shares Authorized Under Stock Option Plans Exercise Price Range Exercisable Options Weighted Average Exercise Price1 SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1	30.70
CY2020Q4	us-gaap	Debt Instrument Face Amount DebtInstrumentFaceAmount	670000000.0	USD
CY2020Q4	us-gaap	Collateral Already Posted Aggregate Fair Value CollateralAlreadyPostedAggregateFairValue	39300000	USD
CY2019Q4	us-gaap	Collateral Already Posted Aggregate Fair Value CollateralAlreadyPostedAggregateFairValue	10100000	USD
CY2019Q4	us-gaap	Derivative Collateral Right To Reclaim Cash DerivativeCollateralRightToReclaimCash	883000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	18537000	USD
CY2020Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	40172000	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Asset DerivativeFairValueOfDerivativeAsset	9600000	USD
CY2019Q4	us-gaap	Derivative Fair Value Of Derivative Liability DerivativeFairValueOfDerivativeLiability	11742000	USD
CY2020Q4	us-gaap	Derivative Asset Fair Value Gross Liability DerivativeAssetFairValueGrossLiability	0	USD
CY2020Q4	us-gaap	Derivative Liability Fair Value Gross Asset DerivativeLiabilityFairValueGrossAsset	0	USD
CY2019Q4	us-gaap	Derivative Asset Fair Value Gross Liability DerivativeAssetFairValueGrossLiability	1569000	USD
CY2019Q4	us-gaap	Derivative Liability Fair Value Gross Asset DerivativeLiabilityFairValueGrossAsset	1569000	USD
CY2020Q4	us-gaap	Derivative Asset Collateral Obligation To Return Cash Offset DerivativeAssetCollateralObligationToReturnCashOffset	0	USD
CY2020Q4	us-gaap	Derivative Liability Collateral Right To Reclaim Cash Offset DerivativeLiabilityCollateralRightToReclaimCashOffset	39270000	USD
CY2019Q4	us-gaap	Derivative Asset Collateral Obligation To Return Cash Offset DerivativeAssetCollateralObligationToReturnCashOffset	0	USD
CY2019Q4	us-gaap	Derivative Liability Collateral Right To Reclaim Cash Offset DerivativeLiabilityCollateralRightToReclaimCashOffset	10117000	USD
CY2020Q4	us-gaap	Derivative Assets DerivativeAssets	18537000	USD
CY2020Q4	us-gaap	Derivative Liabilities DerivativeLiabilities	902000	USD
CY2019Q4	us-gaap	Derivative Assets DerivativeAssets	8031000	USD
CY2019Q4	us-gaap	Derivative Liabilities DerivativeLiabilities	56000	USD
CY2020	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.30
CY2019	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.26
CY2018	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	1.20
CY2020	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	47157	shares
CY2020	sbsi	Stock Issued During Period Per Share Average Dividend Reinvestment Plan StockIssuedDuringPeriodPerShareAverageDividendReinvestmentPlan	30.21
CY2019	us-gaap	Stock Issued During Period Shares Dividend Reinvestment Plan StockIssuedDuringPeriodSharesDividendReinvestmentPlan	42438	shares
CY2019	sbsi	Stock Issued During Period Per Share Average Dividend Reinvestment Plan StockIssuedDuringPeriodPerShareAverageDividendReinvestmentPlan	34.04
CY2020	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	1035901	shares
CY2020	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	31000000.0	USD
CY2019	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	66467	shares
CY2019	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	2200000	USD
CY2018	us-gaap	Treasury Stock Shares Acquired TreasuryStockSharesAcquired	1459148	shares
CY2018	us-gaap	Treasury Stock Value Acquired Cost Method TreasuryStockValueAcquiredCostMethod	47200000	USD
CY2020	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	15766000	USD
CY2019	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	13099000	USD
CY2018	us-gaap	Current Income Tax Expense Benefit CurrentIncomeTaxExpenseBenefit	4009000	USD
CY2020	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	-4430000	USD
CY2019	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	122000	USD
CY2018	us-gaap	Deferred Income Tax Expense Benefit DeferredIncomeTaxExpenseBenefit	6154000	USD
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	11336000	USD
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13221000	USD
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	10163000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	10291000	USD
CY2020Q4	sbsi	Deferred Tax Liabilities Pension Plan DeferredTaxLiabilitiesPensionPlan	1582000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	9057000	USD
CY2020Q4	sbsi	Deferred Tax Asset Operating Lease Liabilities DeferredTaxAssetOperatingLeaseLiabilities	3514000	USD
CY2020Q4	sbsi	Deferred Tax Liabilities Operating Lease Right Of Use Assets DeferredTaxLiabilitiesOperatingLeaseRightOfUseAssets	3163000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	1385000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities Investments DeferredTaxLiabilitiesInvestments	30940000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	4543000	USD
CY2020Q4	sbsi	Deferred Tax Asset Fair Value Adjustmenton Acquired Loans DeferredTaxAssetFairValueAdjustmentonAcquiredLoans	1037000	USD
CY2020Q4	sbsi	Deferred Tax Assets Unfunded Status Of Defined Benefit Plan DeferredTaxAssetsUnfundedStatusOfDefinedBenefitPlan	7950000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards General Business DeferredTaxAssetsTaxCreditCarryforwardsGeneralBusiness	362000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	1105000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Other DeferredTaxAssetsOther	1776000	USD
CY2020Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	30578000	USD
CY2020Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	46127000	USD
CY2020Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	15549000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Reserves And Accruals Provision For Loan Losses DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsProvisionForLoanLosses	5207000	USD
CY2019Q4	sbsi	Deferred Tax Liabilities Pension Plan DeferredTaxLiabilitiesPensionPlan	2179000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Property Plant And Equipment DeferredTaxLiabilitiesPropertyPlantAndEquipment	6842000	USD
CY2019Q4	sbsi	Deferred Tax Asset Operating Lease Liabilities DeferredTaxAssetOperatingLeaseLiabilities	2137000	USD
CY2019Q4	sbsi	Deferred Tax Liabilities Operating Lease Right Of Use Assets DeferredTaxLiabilitiesOperatingLeaseRightOfUseAssets	2049000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Goodwill And Intangible Assets Intangible Assets DeferredTaxLiabilitiesGoodwillAndIntangibleAssetsIntangibleAssets	1990000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Investments DeferredTaxLiabilitiesInvestments	10278000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Derivative Instruments DeferredTaxAssetsDerivativeInstruments	445000	USD
CY2019Q4	sbsi	Deferred Tax Asset Fair Value Adjustmenton Acquired Loans DeferredTaxAssetFairValueAdjustmentonAcquiredLoans	1478000	USD
CY2019Q4	sbsi	Deferred Tax Assets Unfunded Status Of Defined Benefit Plan DeferredTaxAssetsUnfundedStatusOfDefinedBenefitPlan	8540000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Credit Carryforwards General Business DeferredTaxAssetsTaxCreditCarryforwardsGeneralBusiness	423000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Tax Deferred Expense Compensation And Benefits Share Based Compensation Cost DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefitsShareBasedCompensationCost	914000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities Other DeferredTaxLiabilitiesOther	629000	USD
CY2019Q4	us-gaap	Deferred Tax Assets Gross DeferredTaxAssetsGross	19144000	USD
CY2019Q4	us-gaap	Deferred Income Tax Liabilities DeferredIncomeTaxLiabilities	23967000	USD
CY2019Q4	us-gaap	Deferred Tax Liabilities DeferredTaxLiabilities	4823000	USD
CY2020	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	19633000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2019	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	18433000	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2018	us-gaap	Income Tax Reconciliation Income Tax Expense Benefit At Federal Statutory Income Tax Rate IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate	17703000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation At Federal Statutory Income Tax Rate EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate	0.210
CY2020	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	0
CY2019	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	0	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	0
CY2018	us-gaap	Income Tax Reconciliation Change In Enacted Tax Rate IncomeTaxReconciliationChangeInEnactedTaxRate	-767000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Change In Enacted Tax Rate EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate	-0.009
CY2020	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsuranceAmount	8137000	USD
CY2020	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsurancePercent	0.087
CY2019	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsuranceAmount	4875000	USD
CY2019	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsurancePercent	0.055
CY2018	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsuranceAmount	6257000	USD
CY2018	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Other Than Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeOtherThanLifeInsurancePercent	0.074
CY2020	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	536000	USD
CY2020	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsurancePercent	0.006
CY2019	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	484000	USD
CY2019	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsurancePercent	0.005
CY2018	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Amount EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsuranceAmount	613000	USD
CY2018	sbsi	Effective Income Tax Rate Reconciliation Tax Exempt Income Life Insurance Percent EffectiveIncomeTaxRateReconciliationTaxExemptIncomeLifeInsurancePercent	0.007
CY2020	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-70000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.001
CY2019	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-167000	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.002
CY2018	us-gaap	Income Tax Reconciliation Nondeductible Expense Share Based Compensation Cost IncomeTaxReconciliationNondeductibleExpenseShareBasedCompensationCost	-191000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Nondeductible Expense Share Based Compensation Cost EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost	-0.002
CY2020	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	329000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.004
CY2019	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	217000	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.002
CY2018	us-gaap	Income Tax Reconciliation State And Local Income Taxes IncomeTaxReconciliationStateAndLocalIncomeTaxes	297000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation State And Local Income Taxes EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes	0.003
CY2020	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	117000	USD
CY2020	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.001
CY2019	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	97000	USD
CY2019	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0.001
CY2018	us-gaap	Income Tax Reconciliation Other Adjustments IncomeTaxReconciliationOtherAdjustments	-9000	USD
CY2018	us-gaap	Effective Income Tax Rate Reconciliation Other Adjustments EffectiveIncomeTaxRateReconciliationOtherAdjustments	0
CY2020	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	11336000	USD
CY2020	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.121
CY2019	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	13221000	USD
CY2019	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.151
CY2018	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	10163000	USD
CY2018	us-gaap	Effective Income Tax Rate Continuing Operations EffectiveIncomeTaxRateContinuingOperations	0.121
CY2019Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	0	USD
CY2020Q4	us-gaap	Deferred Tax Assets Valuation Allowance DeferredTaxAssetsValuationAllowance	0	USD
CY2020Q4	us-gaap	Lessee Operating Lease Renewal Term LesseeOperatingLeaseRenewalTerm	P10Y
CY2020Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	15063000	USD
CY2019Q4	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	9755000	USD
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	16734000	USD
CY2019Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	10174000	USD
CY2020	us-gaap	Operating Lease Cost OperatingLeaseCost	2193000	USD
CY2019	us-gaap	Operating Lease Cost OperatingLeaseCost	1595000	USD
CY2018	us-gaap	Operating Lease Cost OperatingLeaseCost	1764000	USD
CY2020	us-gaap	Operating Lease Payments OperatingLeasePayments	1479000	USD
CY2019	us-gaap	Operating Lease Payments OperatingLeasePayments	1465000	USD
CY2020	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	7912000	USD
CY2019	us-gaap	Right Of Use Asset Obtained In Exchange For Operating Lease Liability RightOfUseAssetObtainedInExchangeForOperatingLeaseLiability	1205000	USD
CY2020Q2	sbsi	Lessee Operating Lease Numberof Contracts LesseeOperatingLeaseNumberofContracts	1	contract
CY2020Q4	us-gaap	Operating Lease Liability OperatingLeaseLiability	16734000	USD
CY2020Q2	us-gaap	Operating Lease Right Of Use Asset OperatingLeaseRightOfUseAsset	6600000	USD
CY2020Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P15Y9M18D
CY2019Q4	us-gaap	Operating Lease Weighted Average Remaining Lease Term1 OperatingLeaseWeightedAverageRemainingLeaseTerm1	P12Y2M12D
CY2020Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0301	Rate
CY2019Q4	us-gaap	Operating Lease Weighted Average Discount Rate Percent OperatingLeaseWeightedAverageDiscountRatePercent	0.0382	Rate
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Next Twelve Months LesseeOperatingLeaseLiabilityPaymentsDueNextTwelveMonths	1831000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Two LesseeOperatingLeaseLiabilityPaymentsDueYearTwo	1518000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Three LesseeOperatingLeaseLiabilityPaymentsDueYearThree	1379000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Four LesseeOperatingLeaseLiabilityPaymentsDueYearFour	1225000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due Year Five LesseeOperatingLeaseLiabilityPaymentsDueYearFive	1220000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due After Year Five LesseeOperatingLeaseLiabilityPaymentsDueAfterYearFive	14037000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Payments Due LesseeOperatingLeaseLiabilityPaymentsDue	21210000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Liability Undiscounted Excess Amount LesseeOperatingLeaseLiabilityUndiscountedExcessAmount	4476000	USD
CY2020Q4	sbsi	Lessee Operating Lease Lease Not Yet Commenced Payments Due LesseeOperatingLeaseLeaseNotYetCommencedPaymentsDue	1400000	USD
CY2020Q4	us-gaap	Lessee Operating Lease Lease Not Yet Commenced Term Of Contract1 LesseeOperatingLeaseLeaseNotYetCommencedTermOfContract1	P13Y
CY2020Q4	us-gaap	Net Rentable Area NetRentableArea	202000	sqft
CY2020Q4	sbsi	Numberof Square Feet Occupied NumberofSquareFeetOccupied	39000	sqft
CY2020	us-gaap	Operating Lease Lease Income OperatingLeaseLeaseIncome	3277000	USD
CY2019	us-gaap	Operating Lease Lease Income OperatingLeaseLeaseIncome	2991000	USD
CY2018	us-gaap	Operating Lease Lease Income OperatingLeaseLeaseIncome	2987000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Next Twelve Months LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths	3021000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Two Years LessorOperatingLeasePaymentsToBeReceivedTwoYears	2064000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Three Years LessorOperatingLeasePaymentsToBeReceivedThreeYears	1718000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Four Years LessorOperatingLeasePaymentsToBeReceivedFourYears	1415000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Five Years LessorOperatingLeasePaymentsToBeReceivedFiveYears	1148000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received Thereafter LessorOperatingLeasePaymentsToBeReceivedThereafter	1741000	USD
CY2020Q4	us-gaap	Lessor Operating Lease Payments To Be Received LessorOperatingLeasePaymentsToBeReceived	11107000	USD
CY2019Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1455000	USD
CY2018Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1890000	USD
CY2017Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1971000	USD
CY2020	us-gaap	Off Balance Sheet Credit Loss Liability Credit Loss Expense Reversal OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal	91000	USD
CY2019	us-gaap	Off Balance Sheet Credit Loss Liability Credit Loss Expense Reversal OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal	-435000	USD
CY2018	us-gaap	Off Balance Sheet Credit Loss Liability Credit Loss Expense Reversal OffBalanceSheetCreditLossLiabilityCreditLossExpenseReversal	-81000	USD
CY2020Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	6386000	USD
CY2019Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1455000	USD
CY2018Q4	us-gaap	Off Balance Sheet Credit Loss Liability OffBalanceSheetCreditLossLiability	1890000	USD
CY2020Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Amount Liability FairValueDisclosureOffbalanceSheetRisksAmountLiability	806796000	USD
CY2019Q4	us-gaap	Fair Value Disclosure Offbalance Sheet Risks Amount Liability FairValueDisclosureOffbalanceSheetRisksAmountLiability	942882000	USD
CY2020Q4	sbsi	Unsettled Trades To Purchase Securities Liability UnsettledTradesToPurchaseSecuritiesLiability	0	USD
CY2020Q4	sbsi	Unsettled Trades To Sell Securities UnsettledTradesToSellSecurities	0	USD
CY2019Q4	sbsi	Unsettled Trades To Purchase Securities Liability UnsettledTradesToPurchaseSecuritiesLiability	17500000	USD
CY2019Q4	sbsi	Unsettled Trades To Sell Securities UnsettledTradesToSellSecurities	0	USD
CY2020Q4	sbsi	Unsettled Issuancesof Brokered C Ds UnsettledIssuancesofBrokeredCDs	0	USD
CY2019Q4	sbsi	Unsettled Issuancesof Brokered C Ds UnsettledIssuancesofBrokeredCDs	20000000.0	USD
CY2020Q4	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	56904000	USD
CY2020Q3	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	55677000	USD
CY2020Q2	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	58495000	USD
CY2020Q1	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	60752000	USD
CY2020Q4	us-gaap	Interest Expense InterestExpense	8197000	USD
CY2020Q3	us-gaap	Interest Expense InterestExpense	9091000	USD
CY2020Q2	us-gaap	Interest Expense InterestExpense	11224000	USD
CY2020Q1	us-gaap	Interest Expense InterestExpense	16051000	USD
CY2020Q4	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	48707000	USD
CY2020Q3	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	46586000	USD
CY2020Q2	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	47271000	USD
CY2020Q1	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	44701000	USD
CY2020Q4	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	-5545000	USD
CY2020Q3	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	-4746000	USD
CY2020Q2	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	5245000	USD
CY2020Q1	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	25247000	USD
CY2020Q4	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	54252000	USD
CY2020Q3	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	51332000	USD
CY2020Q2	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	42026000	USD
CY2020Q1	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	19454000	USD
CY2020Q4	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	10924000	USD
CY2020Q3	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	11063000	USD
CY2020Q2	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	9531000	USD
CY2020Q1	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	9957000	USD
CY2020Q4	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	-24000	USD
CY2020Q3	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	78000	USD
CY2020Q2	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	2662000	USD
CY2020Q1	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	5541000	USD
CY2020Q4	us-gaap	Noninterest Expense NoninterestExpense	31315000	USD
CY2020Q3	us-gaap	Noninterest Expense NoninterestExpense	31616000	USD
CY2020Q2	us-gaap	Noninterest Expense NoninterestExpense	29856000	USD
CY2020Q1	us-gaap	Noninterest Expense NoninterestExpense	30520000	USD
CY2020Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	33837000	USD
CY2020Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	30857000	USD
CY2020Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	24363000	USD
CY2020Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	4432000	USD
CY2020Q4	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	4265000	USD
CY2020Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3783000	USD
CY2020Q2	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2809000	USD
CY2020Q1	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	479000	USD
CY2020Q4	us-gaap	Net Income Loss NetIncomeLoss	29572000	USD
CY2020Q3	us-gaap	Net Income Loss NetIncomeLoss	27074000	USD
CY2020Q2	us-gaap	Net Income Loss NetIncomeLoss	21554000	USD
CY2020Q1	us-gaap	Net Income Loss NetIncomeLoss	3953000	USD
CY2020Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.89
CY2020Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.82
CY2020Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.65
CY2020Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.12
CY2020Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.89
CY2020Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.82
CY2020Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.65
CY2020Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.12
CY2020Q4	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.37
CY2020Q3	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.31
CY2020Q2	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.31
CY2020Q1	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.31
CY2020Q4	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	26.56
CY2020Q3	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	25.37
CY2020Q2	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	24.75
CY2020Q1	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	24.11
CY2019Q4	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	60533000	USD
CY2019Q3	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	60555000	USD
CY2019Q2	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	60672000	USD
CY2019Q1	us-gaap	Interest And Dividend Income Operating InterestAndDividendIncomeOperating	59027000	USD
CY2019Q4	us-gaap	Interest Expense InterestExpense	17357000	USD
CY2019Q3	us-gaap	Interest Expense InterestExpense	18182000	USD
CY2019Q2	us-gaap	Interest Expense InterestExpense	17541000	USD
CY2019Q1	us-gaap	Interest Expense InterestExpense	17902000	USD
CY2019Q4	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	43176000	USD
CY2019Q3	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	42373000	USD
CY2019Q2	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	43131000	USD
CY2019Q1	us-gaap	Interest Income Expense Net InterestIncomeExpenseNet	41125000	USD
CY2019Q4	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	2508000	USD
CY2019Q3	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	1005000	USD
CY2019Q2	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	2506000	USD
CY2019Q1	us-gaap	Provision For Loan And Lease Losses ProvisionForLoanAndLeaseLosses	-918000	USD
CY2019Q4	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	40668000	USD
CY2019Q3	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	41368000	USD
CY2019Q2	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	40625000	USD
CY2019Q1	us-gaap	Interest Income Expense After Provision For Loan Loss InterestIncomeExpenseAfterProvisionForLoanLoss	42043000	USD
CY2019Q4	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	10423000	USD
CY2019Q3	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	11069000	USD
CY2019Q2	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	10838000	USD
CY2019Q1	sbsi	Noninterest Income Excluding Net Gain Loss On Sale Of Securities NoninterestIncomeExcludingNetGainLossOnSaleOfSecurities	9282000	USD
CY2019Q4	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	42000	USD
CY2019Q3	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	42000	USD
CY2019Q2	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	416000	USD
CY2019Q1	us-gaap	Debt Securities Available For Sale Realized Gain Loss DebtSecuritiesAvailableForSaleRealizedGainLoss	256000	USD
CY2019Q4	us-gaap	Noninterest Expense NoninterestExpense	30944000	USD
CY2019Q3	us-gaap	Noninterest Expense NoninterestExpense	29026000	USD
CY2019Q2	us-gaap	Noninterest Expense NoninterestExpense	29700000	USD
CY2019Q1	us-gaap	Noninterest Expense NoninterestExpense	29627000	USD
CY2019Q4	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	20189000	USD
CY2019Q3	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	23453000	USD
CY2019Q2	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	22179000	USD
CY2019Q1	us-gaap	Income Loss From Continuing Operations Before Income Taxes Minority Interest And Income Loss From Equity Method Investments IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments	21954000	USD
CY2019Q4	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	2854000	USD
CY2019Q3	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3661000	USD
CY2019Q2	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3569000	USD
CY2019Q1	us-gaap	Income Tax Expense Benefit IncomeTaxExpenseBenefit	3137000	USD
CY2019Q4	us-gaap	Net Income Loss NetIncomeLoss	17335000	USD
CY2019Q3	us-gaap	Net Income Loss NetIncomeLoss	19792000	USD
CY2019Q2	us-gaap	Net Income Loss NetIncomeLoss	18610000	USD
CY2019Q1	us-gaap	Net Income Loss NetIncomeLoss	18817000	USD
CY2019Q4	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.51
CY2019Q3	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.59
CY2019Q2	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.55
CY2019Q1	us-gaap	Earnings Per Share Basic EarningsPerShareBasic	0.56
CY2019Q4	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.51
CY2019Q3	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.58
CY2019Q2	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.55
CY2019Q1	us-gaap	Earnings Per Share Diluted EarningsPerShareDiluted	0.56
CY2019Q4	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.34
CY2019Q3	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.31
CY2019Q2	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.31
CY2019Q1	us-gaap	Common Stock Dividends Per Share Cash Paid CommonStockDividendsPerShareCashPaid	0.30
CY2019Q4	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	23.79
CY2019Q3	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	23.98
CY2019Q2	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	23.34
CY2019Q1	sbsi	Bookvaluepercommonshare Bookvaluepercommonshare	22.48

Files In Submission

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$SBSI
SOUTHSIDE BANCSHARES INC Stock $sbsi

2020 Q4 Form 10-K Financial Statement

#000070543221000013 Filed on February 26, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$SBSI SOUTHSIDE BANCSHARES INC Stock $sbsi

2020 Q4 Form 10-K Financial Statement

#000070543221000013 Filed on February 26, 2021

Income Statement

Balance Sheet

Cashflow Statement

Facts In Submission

Files In Submission

$SBSI
SOUTHSIDE BANCSHARES INC Stock $sbsi