<?xml version="1.0" encoding="utf-8"?>
<FilingSummary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
  <Version>2.3.0.11</Version>
  <ProcessingTime />
  <ReportFormat>Html</ReportFormat>
  <ReportType />
  <ContextCount>99</ContextCount>
  <ElementCount>86</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>72</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>2</UnitCount>
  <MyReports>
    <Report>
      <IsDefault>true</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>001001 - Document - Document And Entity Information {Elements}</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/DocumentDocumentandEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>011002 - Document - Risk/Return Summary {Unlabeled} (SDIT MONEY MARKET FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006775Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT MONEY MARKET FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R7.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>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>061008 - Document - Risk/Return Summary {Unlabeled} (SDIT PRIME OBLIGATION FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008265Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT PRIME OBLIGATION FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>061013 - Disclosure - Risk/Return Detail Data {Elements} (SDIT PRIME OBLIGATION FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008265Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT PRIME OBLIGATION FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>061014 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006773Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>061019 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006773Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>061020 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT II FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006776Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT II FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>061025 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT II FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006776Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT II FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>061026 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008270Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>061031 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008270Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>061032 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY II FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006774Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY II FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>061037 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY II FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006774Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY II FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>061038 - Document - Risk/Return Summary {Unlabeled} (SDIT MONEY MARKET FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006775Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT MONEY MARKET FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>061043 - Disclosure - Risk/Return Detail Data {Elements} (SDIT MONEY MARKET FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006775Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT MONEY MARKET FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>061044 - Document - Risk/Return Summary {Unlabeled} (SDIT PRIME OBLIGATION FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008265Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT PRIME OBLIGATION FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>061049 - Disclosure - Risk/Return Detail Data {Elements} (SDIT PRIME OBLIGATION FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008265Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT PRIME OBLIGATION FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>061050 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006773Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>061055 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006773Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>061056 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT II FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006776Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT II FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>061061 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT II FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006776Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT II FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>061062 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008270Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>061067 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008270Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>061068 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY II FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006774Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY II FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>061073 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY II FUND - CLASS B)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006774Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY II FUND - CLASS B)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>061074 - Document - Risk/Return Summary {Unlabeled} (SDIT MONEY MARKET FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006775Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT MONEY MARKET FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>061079 - Disclosure - Risk/Return Detail Data {Elements} (SDIT MONEY MARKET FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006775Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT MONEY MARKET FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>061080 - Document - Risk/Return Summary {Unlabeled} (SDIT PRIME OBLIGATION FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008265Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT PRIME OBLIGATION FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>061085 - Disclosure - Risk/Return Detail Data {Elements} (SDIT PRIME OBLIGATION FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008265Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT PRIME OBLIGATION FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>061086 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006773Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>061091 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006773Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>061092 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT II FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006776Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT II FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>061097 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT II FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006776Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT II FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>061098 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008270Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>061103 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008270Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>061104 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY II FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006774Member3</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY II FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>061109 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY II FUND - CLASS C)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006774Member3</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY II FUND - CLASS C)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>061110 - Document - Risk/Return Summary {Unlabeled} (SDIT MONEY MARKET FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006775Member4</Role>
      <ShortName>Risk/Return Summary  (SDIT MONEY MARKET FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>061115 - Disclosure - Risk/Return Detail Data {Elements} (SDIT MONEY MARKET FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006775Member4</Role>
      <ShortName>Risk/Return Detail Data  (SDIT MONEY MARKET FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>061116 - Document - Risk/Return Summary {Unlabeled} (SDIT PRIME OBLIGATION FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008265Member4</Role>
      <ShortName>Risk/Return Summary  (SDIT PRIME OBLIGATION FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>061121 - Disclosure - Risk/Return Detail Data {Elements} (SDIT PRIME OBLIGATION FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008265Member4</Role>
      <ShortName>Risk/Return Detail Data  (SDIT PRIME OBLIGATION FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>061122 - Document - Risk/Return Summary {Unlabeled} (SDIT GOVERNMENT FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000006773Member4</Role>
      <ShortName>Risk/Return Summary  (SDIT GOVERNMENT FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>061127 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GOVERNMENT FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000006773Member4</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GOVERNMENT FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R128.htm</HtmlFileName>
      <LongName>061128 - Document - Risk/Return Summary {Unlabeled} (SDIT TREASURY FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008270Member4</Role>
      <ShortName>Risk/Return Summary  (SDIT TREASURY FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R133.htm</HtmlFileName>
      <LongName>061133 - Disclosure - Risk/Return Detail Data {Elements} (SDIT TREASURY FUND - SWEEP CLASS)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008270Member4</Role>
      <ShortName>Risk/Return Detail Data  (SDIT TREASURY FUND - SWEEP CLASS)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R134.htm</HtmlFileName>
      <LongName>061134 - Document - Risk/Return Summary {Unlabeled} (SDIT PRIME OBLIGATION FUND - CLASS H)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008265Member5</Role>
      <ShortName>Risk/Return Summary  (SDIT PRIME OBLIGATION FUND - CLASS H)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R139.htm</HtmlFileName>
      <LongName>061139 - Disclosure - Risk/Return Detail Data {Elements} (SDIT PRIME OBLIGATION FUND - CLASS H)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008265Member5</Role>
      <ShortName>Risk/Return Detail Data  (SDIT PRIME OBLIGATION FUND - CLASS H)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R140.htm</HtmlFileName>
      <LongName>061140 - Document - Risk/Return Summary {Unlabeled} (SDIT ULTRA SHORT DURATION BOND FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008266Member1</Role>
      <ShortName>Risk/Return Summary  (SDIT ULTRA SHORT DURATION BOND FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R146.htm</HtmlFileName>
      <LongName>061146 - Disclosure - Risk/Return Detail Data {Elements} (SDIT ULTRA SHORT DURATION BOND FUND - CLASS A)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008266Member1</Role>
      <ShortName>Risk/Return Detail Data  (SDIT ULTRA SHORT DURATION BOND FUND - CLASS A)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R147.htm</HtmlFileName>
      <LongName>061147 - Document - Risk/Return Summary {Unlabeled} (SDIT SHORT-DURATION GOVERNMENT FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008267Member</Role>
      <ShortName>Risk/Return Summary  (SDIT SHORT-DURATION GOVERNMENT FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R153.htm</HtmlFileName>
      <LongName>061153 - Disclosure - Risk/Return Detail Data {Elements} (SDIT SHORT-DURATION GOVERNMENT FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008267Member</Role>
      <ShortName>Risk/Return Detail Data  (SDIT SHORT-DURATION GOVERNMENT FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R154.htm</HtmlFileName>
      <LongName>061154 - Document - Risk/Return Summary {Unlabeled} (SDIT INTERMEDIATE-DURATION GOVERNMENT FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008268Member</Role>
      <ShortName>Risk/Return Summary  (SDIT INTERMEDIATE-DURATION GOVERNMENT FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R160.htm</HtmlFileName>
      <LongName>061160 - Disclosure - Risk/Return Detail Data {Elements} (SDIT INTERMEDIATE-DURATION GOVERNMENT FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008268Member</Role>
      <ShortName>Risk/Return Detail Data  (SDIT INTERMEDIATE-DURATION GOVERNMENT FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R161.htm</HtmlFileName>
      <LongName>061161 - Document - Risk/Return Summary {Unlabeled} (SDIT GNMA FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008269Member</Role>
      <ShortName>Risk/Return Summary  (SDIT GNMA FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R167.htm</HtmlFileName>
      <LongName>061167 - Disclosure - Risk/Return Detail Data {Elements} (SDIT GNMA FUND)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008269Member</Role>
      <ShortName>Risk/Return Detail Data  (SDIT GNMA FUND)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>true</ContainEmbeddedReports>
      <HtmlFileName>R168.htm</HtmlFileName>
      <LongName>061168 - Document - Risk/Return Summary {Unlabeled} (SDIT ULTRA SHORT DURATION BOND FUND - CLASS G)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturn_S000008266Member2</Role>
      <ShortName>Risk/Return Summary  (SDIT ULTRA SHORT DURATION BOND FUND - CLASS G)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <HtmlFileName>R174.htm</HtmlFileName>
      <LongName>061174 - Disclosure - Risk/Return Detail Data {Elements} (SDIT ULTRA SHORT DURATION BOND FUND - CLASS G)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.seic.com/role/RiskReturnDetailData_S000008266Member2</Role>
      <ShortName>Risk/Return Detail Data  (SDIT ULTRA SHORT DURATION BOND FUND - CLASS G)</ShortName>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <ContainEmbeddedReports>false</ContainEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <Logs>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
    <Log type="Info">Element rr_DistributionAndService12b1FeesOverAssets had a mix of decimals attribute values: 4 2.</Log>
  </Logs>
  <InputFiles>
    <File>ck0000701939-20110131.xml</File>
    <File>ck0000701939-20110131.xsd</File>
    <File>ck0000701939-20110131_cal.xml</File>
    <File>ck0000701939-20110131_def.xml</File>
    <File>ck0000701939-20110131_lab.xml</File>
    <File>ck0000701939-20110131_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>
    <File>BarChart21.jpg</File>
    <File>BarChart22.jpg</File>
    <File>BarChart23.jpg</File>
    <File>BarChart24.jpg</File>
    <File>BarChart25.jpg</File>
    <File>BarChart26.jpg</File>
    <File>BarChart27.jpg</File>
    <File>BarChart28.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies />
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
