Document And Entity Information Note To Financial Statement Details Textual Document Fiscal Period Focus EBP 20-2451671 002 [Member] EBP 20-2451671 002 EBP, Basis of Accounting [Policy Text Block] Significant Accounting Policies Document Fiscal Year Focus Note 3 - Fair Value Measurements Schedule H, Line 4i - Schedule of Assets Net assets available for benefits: Note 3 - Fair Value Measurements - Investments at Fair Value (Details) Amendment Flag Schedule of Assets Held at End of Year (Details) Schedule of Assets Held at End of Year 2 (Details) us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentPartyInInterest EBP, Asset Held for Investment, Party-in-Interest [true false] Notes To Financial Statements Notes To Financial Statements [Abstract] dei_DocumentPeriodEndDate Document Period End Date us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseForContribution Total contributions Other income Legal Entity [Axis] dei_EntityTaxIdentificationNumber Entity Tax Identification Number EBP, Investment, Fair Value and NAV [Text Block] Entity [Domain] Entity Central Index Key Net appreciation in investments dei_EntityRegistrantName Entity Registrant Name Entity Current Reporting Status EBP, Description of Plan [Text Block] EBP, Related Party and Party-in-Interest Transactions [Table] Current Fiscal Year End Date us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncrease Total additions sfbs_EmployeeBenefitPlanAgeOfParticipantRequiredToMakeCatchUpContributions Employee Benefit Plan, Age of Participant Required to Make Catch Up Contributions The age of the participant required to make catch up contributions in the employee benefit plan. sfbs_EmployeeBenefitPlanVestingPercentage Employee Benefit Plan, Vesting Percentage (Rate) The vesting percentage in the employee benefit plan. sfbs_EmployeeBenefitPlanMinimumAgeOfParticipant Employee Benefit Plan, Minimum Age of Participant The minimum age of the participant in the employee benefit plan. Entity Shell Company Entity Emerging Growth Company Entity Small Business Investments [Domain] Benefits paid to participants and beneficiaries Accounting Policies [Abstract] sfbs_EmployeeBenefitPlanInvestmentLevel3ReconciliationIncreaseForTransferFromToLevel3 Employee Benefit Plan, Investment, Level 3 Reconciliation, Increase for Transfer from (to) Level 3 Amount of increase in investment, measured using unobservable input, held by employee stock purchase, saving, or similar plan (employee benefit plan (EBP)) from transfer into Level 3 of fair value hierarchy . Rollovers Money Market Funds, Employer Common Stock Funds, and Mutual Funds [Member] Money Market Funds, Employer Common Stock Funds, and Mutual Funds sfbs_EmployeeBenefitPlanTermOfCreditedService Employee Benefit Plan, Term of Credited Service (Year) The term of credited service in the employee benefit plan. sfbs_EmployeeBenefitPlanVestedPercentagePlanTermination Employee Benefit Plan, Vested Percentage, Plan Termination (Rate) The percent of contributions vested in case of plan termination. EBP, Risk and Uncertainty [Table] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecreaseForIncomeLossOnInvestment Total investment income Investments, at contract value Valuation, Cost Approach [Member] Valuation Approach and Technique [Domain] us-gaap-ebp_EmployeeBenefitPlanTaxQualificationStatusExtensibleEnumeration EBP, Tax Qualification Status [Extensible Enumeration] Valuation, Market Approach [Member] Statement of Stockholders' Equity [Abstract] EBP, Tax Status [Text Block] us-gaap-ebp_EmployeeBenefitPlanForfeitedNonvestedAccount EBP, Forfeited Nonvested Account us-gaap-ebp_EmployeeBenefitPlanInvestmentValuationTechniqueExtensibleEnumeration EBP, Investment, Valuation Technique [Extensible Enumeration] EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Current Value Equity Components [Axis] Class of Stock [Axis] Equity Component [Domain] Fair Value, Inputs, Level 2 [Member] us-gaap_PlanNameAxis Plan Name [Axis] Fair Value, Inputs, Level 3 [Member] Interest and dividends Fair Value, Inputs, Level 1 [Member] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitIncreaseDecrease Net increase in net assets available for benefits Deductions Additions EBP, Reconciliation of Financial Statement to Form 5500 [Text Block] EBP, Participant-Directed [Member] Contributions: Investment income: Investments, at fair value Company Plan expenses EBP, Change in Net Asset Available for Benefit, Decrease from Administrative Expense Investment, Identifier [Axis] EBP, Accounting Policy [Table] EBP, Description of Plan [Table] Statement [Table] EBP, Reconciliation of Financial Statement to Form 5500 [Table] EBP, Tax Status [Table] Fair Value Hierarchy and NAV [Domain] us-gaap-ebp_EmployeeBenefitPlanPlanNumber EBP, Plan Number EBP, Risk and Uncertainty [Text Block] Statement of Financial Position [Abstract] us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractLimitationOnTransactingAtContractValueNotProbable EBP, Fully Benefit-Responsive Investment Contract, Limitation on Transacting at Contract Value, Not Probable [true false] us-gaap-ebp_EmployeeBenefitPlanFullyBenefitResponsiveInvestmentContractDescription EBP, Fully Benefit-Responsive Investment Contract, Description EBP, Traditional Guaranteed Investment Contract [Member] EBP, Fully Benefit-Responsive Investment Contract [Text Block] EBP, Investment, Current Value, Type [Extensible Enumeration] sfbs_PolicyTable EBP, Participant-Directed and Nonparticipant-Directed Status [Domain] Investment Type [Axis] us-gaap-ebp_EmployeeBenefitPlanEmployerContributionMatchingPercentage EBP, Employer Contribution, Matching Percentage Mutual Fund [Member] EBP, Schedule of Asset Held for Investment [Text Block] EBP, Use of Estimate [Policy Text Block] EBP, Related Party and Party-in-Interest [Domain] EBP, Other Related Party and Party-in-Interest [Member] EBP, Employer, Common Stock Fund [Member] dei_DocumentType Document Type EBP, Summary of Accounting Policy [Text Block] Document Information [Line Items] EBP, Investment [Policy Text Block] Document Information [Table] EBP, Trustee [Member] Entity Interactive Data Current Statement [Line Items] Fair Value Hierarchy and NAV [Axis] EBP, Related Party and Party-in-Interest [Axis] EBP, Payment to Participant [Policy Text Block] us-gaap-ebp_EmployeeBenefitPlanEmployerContributionParticipantCompensationMatchedPercentage EBP, Employer Contribution, Participant Compensation Matched, Percentage us-gaap-ebp_EmployeeBenefitPlanTaxDeterminationLetterObtained EBP, Tax Determination Letter, Obtained [true false] us-gaap-ebp_EmployeeBenefitPlanAssetHeldForInvestmentInvestmentExcludingPlanInterestInMasterTrustParticipationStatusExtensibleEnumeration EBP, Asset Held for Investment, Investment, Excluding Plan Interest in Master Trust, Participation Status [Extensible Enumeration] us-gaap-ebp_EmployeeBenefitPlanChangeInNetAssetAvailableForBenefitDecrease Total deductions Money Market Funds [Member] EBP, Related Party and Party-in-Interest Transactions [Text Block] us-gaap-ebp_EmployeeBenefitPlanNetAssetAvailableForBenefit Net assets available for benefits Beginning of year End of year EBP, Fully Benefit-Responsive Investment Contract [Table] EBP, Investment, Fair Value and NAV [Table Text Block] us-gaap_PolicyTextBlockAbstract Accounting Policies Participants EBP, Investment, Fair Value and NAV [Table] us-gaap_DisclosureTextBlockAbstract Notes to Financial Statements Retirement Plan Tax Status [Domain] us-gaap_TableTextBlock Notes Tables Qualified Plan [Member]