<?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>2.4.0.8</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ContextCount>116</ContextCount>
  <ElementCount>88</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>72</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000001 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>020000 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT LARGE CAP FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLARGECAPFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT LARGE CAP FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>020005 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT LARGE CAP FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLARGECAPFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT LARGE CAP FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>020006 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT LARGE CAP DIVERSIFIED ALPHA FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLARGECAPDIVERSIFIEDALPHAFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT LARGE CAP DIVERSIFIED ALPHA FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>020011 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT LARGE CAP DIVERSIFIED ALPHA FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLARGECAPDIVERSIFIEDALPHAFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT LARGE CAP DIVERSIFIED ALPHA FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>020012 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT LARGE CAP DISCIPLINED EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLARGECAPDISCIPLINEDEQUITYFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT LARGE CAP DISCIPLINED EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>020017 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT LARGE CAP DISCIPLINED EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLARGECAPDISCIPLINEDEQUITYFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT LARGE CAP DISCIPLINED EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>020018 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT LARGE CAP INDEX FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLARGECAPINDEXFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT LARGE CAP INDEX FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>020023 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT LARGE CAP INDEX FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLARGECAPINDEXFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT LARGE CAP INDEX FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>020024 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT S&amp;P 500 Index Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITSP500IndexFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT S&amp;P 500 Index Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>020027 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT S&amp;P 500 Index Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITSP500IndexFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT S&amp;P 500 Index Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>020028 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Extended Market Index Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITExtendedMarketIndexFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Extended Market Index Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>020031 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Extended Market Index Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITExtendedMarketIndexFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Extended Market Index Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>020032 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT SMALL CAP FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITSMALLCAPFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT SMALL CAP FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>020037 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT SMALL CAP FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITSMALLCAPFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT SMALL CAP FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>020038 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Small Cap II Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITSmallCapIIFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Small Cap II Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>020043 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Small Cap II Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITSmallCapIIFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Small Cap II Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>020044 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT SMALL MID CAP EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITSMALLMIDCAPEQUITYFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT SMALL MID CAP EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>020049 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT SMALL MID CAP EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITSMALLMIDCAPEQUITYFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT SMALL MID CAP EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>020050 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT U.S. Managed Volatility Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITUSManagedVolatilityFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT U.S. Managed Volatility Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>020055 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT U.S. Managed Volatility Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITUSManagedVolatilityFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT U.S. Managed Volatility Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>020056 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT WORLD EQUITY EX-US FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITWORLDEQUITYEXUSFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT WORLD EQUITY EX-US FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>020061 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT WORLD EQUITY EX-US FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITWORLDEQUITYEXUSFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT WORLD EQUITY EX-US FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>020062 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Screened World Equity Ex-US Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITScreenedWorldEquityExUSFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Screened World Equity Ex-US Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>020067 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Screened World Equity Ex-US Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITScreenedWorldEquityExUSFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Screened World Equity Ex-US Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>020068 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT EMERGING MARKETS EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITEMERGINGMARKETSEQUITYFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT EMERGING MARKETS EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>020071 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT EMERGING MARKETS EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITEMERGINGMARKETSEQUITYFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT EMERGING MARKETS EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>020072 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Opportunistic Income Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITOpportunisticIncomeFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Opportunistic Income Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>020077 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Opportunistic Income Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITOpportunisticIncomeFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Opportunistic Income Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>020078 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT CORE FIXED INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITCOREFIXEDINCOME</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT CORE FIXED INCOME</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>020083 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT CORE FIXED INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITCOREFIXEDINCOME</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT CORE FIXED INCOME</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>020084 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT HIGH YIELD BOND FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITHIGHYIELDBONDFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT HIGH YIELD BOND FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>020089 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT HIGH YIELD BOND FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITHIGHYIELDBONDFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT HIGH YIELD BOND FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>020090 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT LONG DURATION FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLONGDURATIONFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT LONG DURATION FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>020095 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT LONG DURATION FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLONGDURATIONFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT LONG DURATION FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>020096 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Long Duration Corporate Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLongDurationCorporateBondFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Long Duration Corporate Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>020101 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Long Duration Corporate Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLongDurationCorporateBondFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Long Duration Corporate Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>020102 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Ultra Short Duration Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITUltraShortDurationBondFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Ultra Short Duration Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>020107 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Ultra Short Duration Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITUltraShortDurationBondFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Ultra Short Duration Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>020108 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT EMERGING MARKETS DEBT FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITEMERGINGMARKETSDEBTFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT EMERGING MARKETS DEBT FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>020113 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT EMERGING MARKETS DEBT FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITEMERGINGMARKETSDEBTFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT EMERGING MARKETS DEBT FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>020114 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Real Return Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITRealReturnFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Real Return Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>020119 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Real Return Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITRealReturnFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Real Return Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>020120 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Limited Duration Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITLimitedDurationBondFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Limited Duration Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>020123 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Limited Duration Bond Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITLimitedDurationBondFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Limited Duration Bond Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>020124 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Dynamic Asset Allocation Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITDynamicAssetAllocationFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Dynamic Asset Allocation Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R131.htm</HtmlFileName>
      <LongName>020129 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Dynamic Asset Allocation Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITDynamicAssetAllocationFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Dynamic Asset Allocation Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R132.htm</HtmlFileName>
      <LongName>020130 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Multi-Asset Real Return Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITMultiAssetRealReturnFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Multi-Asset Real Return Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R137.htm</HtmlFileName>
      <LongName>020135 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Multi-Asset Real Return Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITMultiAssetRealReturnFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Multi-Asset Real Return Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R138.htm</HtmlFileName>
      <LongName>020136 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT Strategic U.S. Large Cap Equity Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITStrategicUSLargeCapEquityFund</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT Strategic U.S. Large Cap Equity Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R141.htm</HtmlFileName>
      <LongName>020139 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT Strategic U.S. Large Cap Equity Fund</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITStrategicUSLargeCapEquityFund</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT Strategic U.S. Large Cap Equity Fund</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>true</HasEmbeddedReports>
      <HtmlFileName>R142.htm</HtmlFileName>
      <LongName>020140 - Document - Risk/Return Summary {Unlabeled} - Class A Prospectus - SIIT GLOBAL EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DocumentRiskReturnSummaryUnlabeledClassAProspectusSIITGLOBALEQUITYFUND</Role>
      <ShortName>Risk/Return Summary  - Class A Prospectus - SIIT GLOBAL EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R145.htm</HtmlFileName>
      <LongName>020143 - Disclosure - Risk/Return Detail Data {Elements} - Class A Prospectus - SIIT GLOBAL EQUITY FUND</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://sei.com/20140926/role/DisclosureRiskReturnDetailDataElementsClassAProspectusSIITGLOBALEQUITYFUND</Role>
      <ShortName>Risk/Return Detail Data  - Class A Prospectus - SIIT GLOBAL EQUITY FUND</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R146.htm</HtmlFileName>
      <LongName>040000 - Disclosure - Risk/Return Detail Data {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/rr/role/RiskReturnDetailData</Role>
      <ShortName>Risk/Return Detail Data</ShortName>
    </Report>
    <Report>
      <IsDefault>true</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs />
  <InputFiles>
    <File>ck0000939934-20140926.xml</File>
    <File>ck0000939934-20140926.xsd</File>
    <File>ck0000939934-20140926_cal.xml</File>
    <File>ck0000939934-20140926_def.xml</File>
    <File>ck0000939934-20140926_lab.xml</File>
    <File>ck0000939934-20140926_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>BarChart1.jpg</File>
    <File>BarChart2.jpg</File>
    <File>BarChart3.jpg</File>
    <File>BarChart4.jpg</File>
    <File>BarChart5.jpg</File>
    <File>BarChart6.jpg</File>
    <File>BarChart7.jpg</File>
    <File>BarChart8.jpg</File>
    <File>BarChart9.jpg</File>
    <File>BarChart10.jpg</File>
    <File>BarChart11.jpg</File>
    <File>BarChart12.jpg</File>
    <File>BarChart13.jpg</File>
    <File>BarChart14.jpg</File>
    <File>BarChart15.jpg</File>
    <File>BarChart16.jpg</File>
    <File>BarChart17.jpg</File>
    <File>BarChart18.jpg</File>
    <File>BarChart19.jpg</File>
    <File>BarChart20.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
