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Loans and Allowance for Probable Loan Losses - Troubled Debt Restructurings (Details) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Mar. 31, 2015
contract
Mar. 31, 2014
contract
Troubled Debt Restructuring [Abstract]    
Extend Amortization Period $ 31sbsi_LoanModificationRelatedToExtendingAmortizationPeriod $ 599sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
Interest Rate Reductions 0sbsi_LoanModificationRelatedToLoweringInterestRates 303sbsi_LoanModificationRelatedToLoweringInterestRates
Combination 1,055sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness [1] 129sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness [1]
Total Modifications 1,086sbsi_FinancingReceivableModificationsTotalModificationsForPeriod 1,031sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
Number of Loans 6us-gaap_FinancingReceivableModificationsNumberOfContracts2 10us-gaap_FinancingReceivableModificationsNumberOfContracts2
1-4 Family Residential    
Troubled Debt Restructuring [Abstract]    
Extend Amortization Period 0sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 0sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Interest Rate Reductions 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 286sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Combination 266sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 [1] 0sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 [1]
Total Modifications 266sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 286sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Number of Loans 2us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember		 1us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ResidentialRealEstateMember
Other    
Troubled Debt Restructuring [Abstract]    
Extend Amortization Period 31sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 338sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Interest Rate Reductions 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Combination 0sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 [1] 25sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 [1]
Total Modifications 31sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 363sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Number of Loans 1us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember		 2us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialRealEstatePortfolioSegmentMember
Commercial Loans    
Troubled Debt Restructuring [Abstract]    
Extend Amortization Period 0sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 261sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember
Interest Rate Reductions 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember
Combination 762sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 [1] 57sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 [1]
Total Modifications 762sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 318sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember
Number of Loans 1us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember		 3us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_CommercialLoanMember
Loans to Individuals    
Troubled Debt Restructuring [Abstract]    
Extend Amortization Period 0sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 0sbsi_LoanModificationRelatedToExtendingAmortizationPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
Interest Rate Reductions 0sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 17sbsi_LoanModificationRelatedToLoweringInterestRates
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
Combination 27sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 [1] 47sbsi_LoanModificationExtendingAmortizationPeriodLoweringInterestRateAndPrincipalForgiveness
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 [1]
Total Modifications $ 27sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 $ 64sbsi_FinancingReceivableModificationsTotalModificationsForPeriod
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
Number of Loans 2us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember		 4us-gaap_FinancingReceivableModificationsNumberOfContracts2
/ us-gaap_FinancingReceivableTroubledDebtRestructuringAxis
= us-gaap_ConsumerLoanMember
[1] These modifications include an extension of the amortization period and interest rate reduction.