<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <Version>2.4.1.9</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>383</ContextCount>
  <ElementCount>556</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>88</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>11</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Consolidated Statements Of Financial Condition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementsOfFinancialCondition</Role>
      <ShortName>Consolidated Statements Of Financial Condition</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00101 - Statement - Consolidated Statements Of Financial Condition (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementsOfFinancialConditionParenthetical</Role>
      <ShortName>Consolidated Statements Of Financial Condition (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Consolidated Statements Of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementsOfOperations</Role>
      <ShortName>Consolidated Statements Of Operations</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Consolidated Statements Of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements Of Comprehensive Income</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Consolidated Statements Of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements Of Cash Flows</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00500 - Statement - Consolidated Statement Of Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementOfShareholdersEquity</Role>
      <ShortName>Consolidated Statement Of Shareholders' Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00501 - Statement - Consolidated Statement of Shareholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/StatementConsolidatedStatementOfShareholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statement of Shareholders' Equity (Parenthetical)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Summary of Significant Accounting And Reporting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureSummaryOfSignificantAccountingAndReportingPolicies</Role>
      <ShortName>Summary of Significant Accounting And Reporting Policies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Disposals</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDisposals</Role>
      <ShortName>Disposals</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecurities</Role>
      <ShortName>Investment Securities</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Loans And Allowance For Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLosses</Role>
      <ShortName>Loans And Allowance For Loan Losses</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Premises And Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosurePremisesAndEquipment</Role>
      <ShortName>Premises And Equipment</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Goodwill And Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureGoodwillAndOtherIntangibleAssets</Role>
      <ShortName>Goodwill And Other Intangible Assets</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDeposits</Role>
      <ShortName>Deposits</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureBorrowedFunds</Role>
      <ShortName>Borrowed Funds</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Trust Preferred Securities and Subordinated Debentures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTrustPreferredSecuritiesAndSubordinatedDebentures</Role>
      <ShortName>Trust Preferred Securities and Subordinated Debentures</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Derivative Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDerivativeInstruments</Role>
      <ShortName>Derivative Instruments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Taxes On Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncome</Role>
      <ShortName>Taxes On Income</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Earnings Per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureEarningsPerCommonShare</Role>
      <ShortName>Earnings Per Common Share</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Capital Requirements and Regulatory Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCapitalRequirementsAndRegulatoryMatters</Role>
      <ShortName>Capital Requirements and Regulatory Matters</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Employee Benefits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureEmployeeBenefits</Role>
      <ShortName>Employee Benefits</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11701 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>11801 - Disclosure - Off Balance Sheet Arrangements, Commitments, Guarantees, And Contractual Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsGuaranteesAndContractualObligations</Role>
      <ShortName>Off Balance Sheet Arrangements, Commitments, Guarantees, And Contractual Obligations</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>11901 - Disclosure - Operating Segments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOperatingSegments</Role>
      <ShortName>Operating Segments</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>12001 - Disclosure - Parent Company Condensed Financial Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureParentCompanyCondensedFinancialInformation</Role>
      <ShortName>Parent Company Condensed Financial Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>12101 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>12201 - Disclosure - New Authoritative Accounting Guidance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureNewAuthoritativeAccountingGuidance</Role>
      <ShortName>New Authoritative Accounting Guidance</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>20102 - Disclosure - Summary Of Significant Accounting And Reporting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureSummaryOfSignificantAccountingAndReportingPoliciess</Role>
      <ShortName>Summary Of Significant Accounting And Reporting Policies</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesTables</Role>
      <ShortName>Investment Securities (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>30403 - Disclosure - Loans And Allowance For Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesTables</Role>
      <ShortName>Loans And Allowance For Loan Losses (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Premises And Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosurePremisesAndEquipmentTables</Role>
      <ShortName>Premises And Equipment (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Goodwill And Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureGoodwillAndOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill And Other Intangible Assets (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureBorrowedFundsTables</Role>
      <ShortName>Borrowed Funds (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Trust Preferred Securities and Subordinated Debentures (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTrustPreferredSecuritiesAndSubordinatedDebenturesTables</Role>
      <ShortName>Trust Preferred Securities and Subordinated Debentures (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Taxes On Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncomeTables</Role>
      <ShortName>Taxes On Income (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Earnings Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureEarningsPerCommonShareTables</Role>
      <ShortName>Earnings Per Common Share (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Capital Requirements And Regulatory Matters (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCapitalRequirementsAndRegulatoryMattersTables</Role>
      <ShortName>Capital Requirements And Regulatory Matters (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>31803 - Disclosure - Off-Balance-Sheet Arrangments, Commitments, Guarantees And Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOffBalanceSheetArrangmentsCommitmentsGuaranteesAndContingenciesTables</Role>
      <ShortName>Off-Balance-Sheet Arrangments, Commitments, Guarantees And Contingencies (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>31903 - Disclosure - Operating Segments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOperatingSegmentsTables</Role>
      <ShortName>Operating Segments (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>32003 - Disclosure - Parent Company Condensed Financial Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureParentCompanyCondensedFinancialInformationTables</Role>
      <ShortName>Parent Company Condensed Financial Information (Tables)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Summary Of Significant Accounting And Reporting Policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureSummaryOfSignificantAccountingAndReportingPoliciesDetails</Role>
      <ShortName>Summary Of Significant Accounting And Reporting Policies (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Disposals (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDisposalsNarrativeDetails</Role>
      <ShortName>Disposals (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Investment Securities (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesNarrativeDetails</Role>
      <ShortName>Investment Securities (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>40302 - Disclosure - Investment Securities (Summary Of Amortized Cost And Fair Values Of Investment Securities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesSummaryOfAmortizedCostAndFairValuesOfInvestmentSecuritiesDetails</Role>
      <ShortName>Investment Securities (Summary Of Amortized Cost And Fair Values Of Investment Securities) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>40303 - Disclosure - Investment Securities (Amortized Cost And Approximate Fair Value Of Investment Securities By Maturity Date) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesAmortizedCostAndApproximateFairValueOfInvestmentSecuritiesByMaturityDateDetails</Role>
      <ShortName>Investment Securities (Amortized Cost And Approximate Fair Value Of Investment Securities By Maturity Date) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>40304 - Disclosure - Investment Securities (Summary Of Sales Of Available For Sale Securities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesSummaryOfSalesOfAvailableForSaleSecuritiesDetails</Role>
      <ShortName>Investment Securities (Summary Of Sales Of Available For Sale Securities) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>40305 - Disclosure - Investment Securities (Summary Of Securities With Gross Unrealized Losses And Their Fair Values) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureInvestmentSecuritiesSummaryOfSecuritiesWithGrossUnrealizedLossesAndTheirFairValuesDetails</Role>
      <ShortName>Investment Securities (Summary Of Securities With Gross Unrealized Losses And Their Fair Values) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Loans And Allowance For Loan Losses (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesNarrativeDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>40402 - Disclosure - Loans And Allowance For Loan Losses (Southwest's Loan Classifications) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesSouthwestSLoanClassificationsDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Southwest's Loan Classifications) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>40403 - Disclosure - Loans And Allowance For Loan Losses (Changes In The Carrying Amounts And Accretable Yields For ASC 310.30 Loans) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesChangesInCarryingAmountsAndAccretableYieldsForAsc31030LoansDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Changes In The Carrying Amounts And Accretable Yields For ASC 310.30 Loans) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>40404 - Disclosure - Loans And Allowance For Loan Losses (Recorded Investment In Loans On Nonaccrual Status) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesRecordedInvestmentInLoansOnNonaccrualStatusDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Recorded Investment In Loans On Nonaccrual Status) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>40405 - Disclosure - Loans And Allowance For Loan Losses (Age Analysis Of Past Due Loans) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesAgeAnalysisOfPastDueLoansDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Age Analysis Of Past Due Loans) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>40406 - Disclosure - Loans And Allowance For Loan Losses (Impaired Loans) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesImpairedLoansDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Impaired Loans) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>40407 - Disclosure - Loans And Allowance For Loan Losses (Average Recorded Investment And Interest Income Recognized On Impaired Loans) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesAverageRecordedInvestmentAndInterestIncomeRecognizedOnImpairedLoansDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Average Recorded Investment And Interest Income Recognized On Impaired Loans) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>40408 - Disclosure - Loans And Allowance For Loan Losses (Troubled Debt Restructured Loans Outstanding) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesTroubledDebtRestructuredLoansOutstandingDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Troubled Debt Restructured Loans Outstanding) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>40409 - Disclosure - Loans And Allowance For Loan Losses (Loans Modified As Troubled Debt Restructurings) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesLoansModifiedAsTroubledDebtRestructuringsDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Loans Modified As Troubled Debt Restructurings) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>40410 - Disclosure - Loans And Allowance For Loan Losses (Recorded Investment And The Number Of Loans Modified As Troubled Debt Restructuring Which Subsequently Defaulted) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesRecordedInvestmentAndNumberOfLoansModifiedAsTroubledDebtRestructuringWhichSubsequentlyDefaultedDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Recorded Investment And The Number Of Loans Modified As Troubled Debt Restructuring Which Subsequently Defaulted) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>40411 - Disclosure - Loans And Allowance For Loan Losses (Classification Of Risk Category Of Loans, By Classes) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesClassificationOfRiskCategoryOfLoansByClassesDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (Classification Of Risk Category Of Loans, By Classes) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>40412 - Disclosure - Loans And Allowance For Loan Losses (By Balance In The Allowance For Loan Losses And The Recorded Investment In Loans Portfolio Classification Disaggregated On The Basis Of Impairment Evaluation Method) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureLoansAndAllowanceForLoanLossesByBalanceInAllowanceForLoanLossesAndRecordedInvestmentInLoansPortfolioClassificationDisaggregatedOnBasisOfImpairmentEvaluationMethodDetails</Role>
      <ShortName>Loans And Allowance For Loan Losses (By Balance In The Allowance For Loan Losses And The Recorded Investment In Loans Portfolio Classification Disaggregated On The Basis Of Impairment Evaluation Method) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Premises And Equipment (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosurePremisesAndEquipmentNarrativeDetails</Role>
      <ShortName>Premises And Equipment (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>40502 - Disclosure - Premises And Equipment (Premises And Equipment) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosurePremisesAndEquipmentPremisesAndEquipmentDetails</Role>
      <ShortName>Premises And Equipment (Premises And Equipment) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>40503 - Disclosure - Premises And Equipment (Future Minimum Annual Rental Payments) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosurePremisesAndEquipmentFutureMinimumAnnualRentalPaymentsDetails</Role>
      <ShortName>Premises And Equipment (Future Minimum Annual Rental Payments) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Goodwill And Other Intangible Assets (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureGoodwillAndOtherIntangibleAssetsNarrativeDetails</Role>
      <ShortName>Goodwill And Other Intangible Assets (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Goodwill and Other Intangible Assets (Gross Carrying Amount of Other Intangible Assets and Accumulated Amortization) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureGoodwillAndOtherIntangibleAssetsGrossCarryingAmountOfOtherIntangibleAssetsAndAccumulatedAmortizationDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets (Gross Carrying Amount of Other Intangible Assets and Accumulated Amortization) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>40603 - Disclosure - Goodwill and Other Intangible Assets (Estimated Aggregate Future Amortization Expense for Other Intangible Assets) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureGoodwillAndOtherIntangibleAssetsEstimatedAggregateFutureAmortizationExpenseForOtherIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets (Estimated Aggregate Future Amortization Expense for Other Intangible Assets) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Fair Value Measurements (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurementsNarrativeDetails</Role>
      <ShortName>Fair Value Measurements (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>40702 - Disclosure - Fair Value Measurements (Summary Of Financial Assets Measured At Fair Value On A Recurring Basis) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements (Summary Of Financial Assets Measured At Fair Value On A Recurring Basis) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>40703 - Disclosure - Fair Value Measurements (Asset Measured At Fair Value On A Nonrecurring Basis) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurementsAssetMeasuredAtFairValueOnNonrecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements (Asset Measured At Fair Value On A Nonrecurring Basis) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>40704 - Disclosure - Fair Value Measurements (Carrying Values And Estimated Fair Values Of Financial Instruments Segregated By The Level Of The Valuation Inputs) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureFairValueMeasurementsCarryingValuesAndEstimatedFairValuesOfFinancialInstrumentsSegregatedByLevelOfValuationInputsDetails</Role>
      <ShortName>Fair Value Measurements (Carrying Values And Estimated Fair Values Of Financial Instruments Segregated By The Level Of The Valuation Inputs) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Deposits (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDepositsNarrativeDetails</Role>
      <ShortName>Deposits (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>40802 - Disclosure - Deposits (Schedule Of Deposits) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDepositsScheduleOfDepositsDetails</Role>
      <ShortName>Deposits (Schedule Of Deposits) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>40803 - Disclosure - Deposits (Time Deposits Maturities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDepositsTimeDepositsMaturitiesDetails</Role>
      <ShortName>Deposits (Time Deposits Maturities) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Borrowed Funds (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureBorrowedFundsNarrativeDetails</Role>
      <ShortName>Borrowed Funds (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>40902 - Disclosure - Borrowed Funds (Schedule Of Borrowed Funds) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureBorrowedFundsScheduleOfBorrowedFundsDetails</Role>
      <ShortName>Borrowed Funds (Schedule Of Borrowed Funds) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Trust Preferred Securities and Subordinated Debentures (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTrustPreferredSecuritiesAndSubordinatedDebenturesNarrativeDetails</Role>
      <ShortName>Trust Preferred Securities and Subordinated Debentures (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>41002 - Disclosure - Trust Preferred Securities and Subordinated Debentures (Schedule of Trust Preferred Securities) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTrustPreferredSecuritiesAndSubordinatedDebenturesScheduleOfTrustPreferredSecuritiesDetails</Role>
      <ShortName>Trust Preferred Securities and Subordinated Debentures (Schedule of Trust Preferred Securities) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureDerivativeInstrumentsDetails</Role>
      <ShortName>Derivative Instruments (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Taxes On Income (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncomeNarrativeDetails</Role>
      <ShortName>Taxes On Income (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>41202 - Disclosure - Taxes On Income (Tax Components) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncomeTaxComponentsDetails</Role>
      <ShortName>Taxes On Income (Tax Components) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>41203 - Disclosure - Taxes On Income (Reconciliation from the Expected Tax Expense (Benefit) Using the U.S. Federal Income Tax Rate) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncomeReconciliationFromExpectedTaxExpenseBenefitUsingUsFederalIncomeTaxRateDetails</Role>
      <ShortName>Taxes On Income (Reconciliation from the Expected Tax Expense (Benefit) Using the U.S. Federal Income Tax Rate) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>41204 - Disclosure - Taxes on Income (Temporary Differences That Give Rise to the Deferred Tax Assets) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureTaxesOnIncomeTemporaryDifferencesThatGiveRiseToDeferredTaxAssetsDetails</Role>
      <ShortName>Taxes on Income (Temporary Differences That Give Rise to the Deferred Tax Assets) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Shareholders' Equity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureShareholdersEquityDetails</Role>
      <ShortName>Shareholders' Equity (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureEarningsPerCommonShareDetails</Role>
      <ShortName>Earnings Per Common Share (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Capital Requirements And Regulatory Agreements (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCapitalRequirementsAndRegulatoryAgreementsNarrativeDetails</Role>
      <ShortName>Capital Requirements And Regulatory Agreements (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Capital Requirements And Regulatory Agreements (Southwest’s and Bank SNB's Actual Capital Amounts And Ratios) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCapitalRequirementsAndRegulatoryAgreementsSouthwestsAndBankSnbSActualCapitalAmountsAndRatiosDetails</Role>
      <ShortName>Capital Requirements And Regulatory Agreements (Southwest’s and Bank SNB's Actual Capital Amounts And Ratios) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Employee Benefits (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureEmployeeBenefitsNarrativeDetails</Role>
      <ShortName>Employee Benefits (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>41701 - Disclosure - Related Party Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureRelatedPartyTransactionsDetails</Role>
      <ShortName>Related Party Transactions (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>41801 - Disclosure - Off-Balance-Sheet Arrangements, Commitments, Guarantees And Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOffBalanceSheetArrangementsCommitmentsGuaranteesAndContingenciesDetails</Role>
      <ShortName>Off-Balance-Sheet Arrangements, Commitments, Guarantees And Contingencies (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>41901 - Disclosure - Operating Segments (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOperatingSegmentsNarrativeDetails</Role>
      <ShortName>Operating Segments (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>41902 - Disclosure - Operating Segments (Financial Results By Operating Segment) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureOperatingSegmentsFinancialResultsByOperatingSegmentDetails</Role>
      <ShortName>Operating Segments (Financial Results By Operating Segment) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>42001 - Disclosure - Parent Company Condensed Financial Information (Statements Of Financial Condition) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureParentCompanyCondensedFinancialInformationStatementsOfFinancialConditionDetails</Role>
      <ShortName>Parent Company Condensed Financial Information (Statements Of Financial Condition) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>42002 - Disclosure - Parent Company Condensed Financial Information (Statements Of Operations) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureParentCompanyCondensedFinancialInformationStatementsOfOperationsDetails</Role>
      <ShortName>Parent Company Condensed Financial Information (Statements Of Operations) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>42003 - Disclosure - Parent Company Condensed Financial Information (Statements Of Cash Flows) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureParentCompanyCondensedFinancialInformationStatementsOfCashFlowsDetails</Role>
      <ShortName>Parent Company Condensed Financial Information (Statements Of Cash Flows) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>42101 - Disclosure - Commitments And Contingencies (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://oksb.com/role/DisclosureCommitmentsAndContingenciesNarrativeDetails</Role>
      <ShortName>Commitments And Contingencies (Narrative) (Details)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Element us-gaap_CollateralAlreadyPostedAggregateFairValue had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">Element us-gaap_Goodwill had a mix of decimals attribute values: -5 -3.</Log>
    <Log type="Info">'Monetary' elements on report '00400 - Statement - Consolidated Statements Of Cash Flows' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40101 - Disclosure - Summary Of Significant Accounting And Reporting Policies (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40401 - Disclosure - Loans And Allowance For Loan Losses (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40701 - Disclosure - Fair Value Measurements (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40801 - Disclosure - Deposits (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '40901 - Disclosure - Borrowed Funds (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41001 - Disclosure - Trust Preferred Securities and Subordinated Debentures (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41101 - Disclosure - Derivative Instruments (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41201 - Disclosure - Taxes On Income (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41601 - Disclosure - Employee Benefits (Narrative) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41801 - Disclosure - Off-Balance-Sheet Arrangements, Commitments, Guarantees And Contingencies (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">'Monetary' elements on report '41902 - Disclosure - Operating Segments (Financial Results By Operating Segment) (Details)' had a mix of different decimal attribute values.</Log>
    <Log type="Info">Process Flow-Through: 00100 - Statement - Consolidated Statements Of Financial Condition</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2012'</Log>
    <Log type="Info">	Process Flow-Through: Removing column 'Dec. 31, 2011'</Log>
    <Log type="Info">Process Flow-Through: 00101 - Statement - Consolidated Statements Of Financial Condition (Parenthetical)</Log>
    <Log type="Info">Process Flow-Through: 00200 - Statement - Consolidated Statements Of Operations</Log>
    <Log type="Info">Process Flow-Through: 00300 - Statement - Consolidated Statements Of Comprehensive Income</Log>
    <Log type="Info">Process Flow-Through: 00400 - Statement - Consolidated Statements Of Cash Flows</Log>
    <Log type="Info">Process Flow-Through: 00501 - Statement - Consolidated Statement of Shareholders' Equity (Parenthetical)</Log>
  </Logs>
  <InputFiles>
    <File>oksb-20141231.xml</File>
    <File>oksb-20141231.xsd</File>
    <File>oksb-20141231_cal.xml</File>
    <File>oksb-20141231_def.xml</File>
    <File>oksb-20141231_lab.xml</File>
    <File>oksb-20141231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles />
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
