<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>210</ContextCount>
  <ElementCount>367</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>59</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Consolidated Balance Sheets (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedBalanceSheetsUnaudited</Role>
      <ShortName>Consolidated Balance Sheets (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Consolidated Balance Sheets (unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedBalanceSheetsUnauditedParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Consolidated Statements of Operations (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedStatementsOfOperationsUnaudited</Role>
      <ShortName>Consolidated Statements of Operations (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Consolidated Statements of Comprehensive Income (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedStatementsOfComprehensiveIncomeUnaudited</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - Consolidated Statements of Stockholders' Equity (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedStatementsOfStockholdersEquityUnaudited</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - Consolidated Statements of Cash Flows (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/StatementConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Consolidated Statements of Cash Flows (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - Basis of Presentation and Recently Issued Accounting Standards</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureBasisOfPresentationAndRecentlyIssuedAccountingStandards</Role>
      <ShortName>Basis of Presentation and Recently Issued Accounting Standards</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Sales Recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognition</Role>
      <ShortName>Sales Recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Assets Held for Sale</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAssetsHeldForSale</Role>
      <ShortName>Assets Held for Sale</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Net Earnings Per Share ("EPS")</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPS</Role>
      <ShortName>Net Earnings Per Share ("EPS")</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Debt, Inventory Financing Facility, Finance Leases and Other Financing Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilityFinanceLeasesAndOtherFinancingObligations</Role>
      <ShortName>Debt, Inventory Financing Facility, Finance Leases and Other Financing Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Share Repurchase Program</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureShareRepurchaseProgram</Role>
      <ShortName>Share Repurchase Program</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Subsequent Event</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSubsequentEvent</Role>
      <ShortName>Subsequent Event</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Basis of Presentation and Recently Issued Accounting Standards (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureBasisOfPresentationAndRecentlyIssuedAccountingStandardsPolicies</Role>
      <ShortName>Basis of Presentation and Recently Issued Accounting Standards (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureBasisOfPresentationAndRecentlyIssuedAccountingStandards</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Sales Recognition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionTables</Role>
      <ShortName>Sales Recognition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognition</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Net Earnings Per Share ("EPS") (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPSTables</Role>
      <ShortName>Net Earnings Per Share ("EPS") (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPS</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilitiesFinanceLeasesAndOtherFinancingObligationsTables</Role>
      <ShortName>Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureLeases</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensation</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformation</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitions</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Basis of Presentation and Recently Issued Accounting Standards - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureBasisOfPresentationAndRecentlyIssuedAccountingStandardsAdditionalInformationDetail</Role>
      <ShortName>Basis of Presentation and Recently Issued Accounting Standards - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Sales Recognition - Summary of Revenue Disaggregated by Reportable Operating Segments (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionSummaryOfRevenueDisaggregatedByReportableOperatingSegmentsDetail</Role>
      <ShortName>Sales Recognition - Summary of Revenue Disaggregated by Reportable Operating Segments (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Sales Recognition - Summary of Information about Receivables and Contract Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionSummaryOfInformationAboutReceivablesAndContractLiabilitiesDetail</Role>
      <ShortName>Sales Recognition - Summary of Information about Receivables and Contract Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Sales Recognition - Summary of Changes in Contract Liabilities from Contract with Customers (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionSummaryOfChangesInContractLiabilitiesFromContractWithCustomersDetail</Role>
      <ShortName>Sales Recognition - Summary of Changes in Contract Liabilities from Contract with Customers (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Sales Recognition - Summary of Estimated Net Sales Related to Performance Obligation (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionSummaryOfEstimatedNetSalesRelatedToPerformanceObligationDetail</Role>
      <ShortName>Sales Recognition - Summary of Estimated Net Sales Related to Performance Obligation (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Sales Recognition - Summary of Estimated Net Sales Related to Performance Obligation (Detail 1)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionSummaryOfEstimatedNetSalesRelatedToPerformanceObligationDetail1</Role>
      <ShortName>Sales Recognition - Summary of Estimated Net Sales Related to Performance Obligation (Detail 1)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Sales Recognition - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSalesRecognitionAdditionalInformationDetail</Role>
      <ShortName>Sales Recognition - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Assets Held for Sale - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAssetsHeldForSaleAdditionalInformationDetail</Role>
      <ShortName>Assets Held for Sale - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Net Earnings Per Share ("EPS") - Reconciliation of Denominators of Basic and Diluted EPS Calculations (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPSReconciliationOfDenominatorsOfBasicAndDilutedEPSCalculationsDetail</Role>
      <ShortName>Net Earnings Per Share ("EPS") - Reconciliation of Denominators of Basic and Diluted EPS Calculations (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPSTables</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Net Earnings Per Share ("EPS") - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPSAdditionalInformationDetail</Role>
      <ShortName>Net Earnings Per Share ("EPS") - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureNetEarningsPerShareEPSTables</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Long-Term Debt (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilitiesFinanceLeasesAndOtherFinancingObligationsLongTermDebtDetail</Role>
      <ShortName>Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Long-Term Debt (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilitiesFinanceLeasesAndOtherFinancingObligationsTables</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilitiesFinanceLeasesAndOtherFinancingObligationsAdditionalInformationDetail</Role>
      <ShortName>Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Schedule of Convertible Senior Notes Balances (Detail)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureDebtInventoryFinancingFacilitiesFinanceLeasesAndOtherFinancingObligationsScheduleOfConvertibleSeniorNotesBalancesDetail</Role>
      <ShortName>Debt, Inventory Financing Facilities, Finance Leases and Other Financing Obligations - Schedule of Convertible Senior Notes Balances (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Leases - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesAdditionalInformationDetail</Role>
      <ShortName>Leases - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Balance Sheet (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfFinancialStatementClassificationOfLeaseBalancesWithConsolidatedBalanceSheetDetail</Role>
      <ShortName>Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Balance Sheet (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Balance Sheet (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfFinancialStatementClassificationOfLeaseBalancesWithConsolidatedBalanceSheetParentheticalDetail</Role>
      <ShortName>Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Balance Sheet (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Statement of Operations (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfFinancialStatementClassificationOfLeaseBalancesWithConsolidatedStatementOfOperationsDetail</Role>
      <ShortName>Leases - Schedule of Financial Statement Classification of Lease Balances With Consolidated Statement of Operations (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100460 - Disclosure - Leases - Schedule of Future Minimum Lease Payments Under Non-cancelable Leases (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfFutureMinimumLeasePaymentsUnderNonCancelableLeasesDetail</Role>
      <ShortName>Leases - Schedule of Future Minimum Lease Payments Under Non-cancelable Leases (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Leases - Schedule of Weighted Average Remaining Term and Discount Rates (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfWeightedAverageRemainingTermAndDiscountRatesDetail</Role>
      <ShortName>Leases - Schedule of Weighted Average Remaining Term and Discount Rates (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Leases - Schedule of Cash Flows Associated With the Company's Leasing Activities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureLeasesScheduleOfCashFlowsAssociatedWithCompanySLeasingActivitiesDetail</Role>
      <ShortName>Leases - Schedule of Cash Flows Associated With the Company's Leasing Activities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100500 - Disclosure - Stock-Based Compensation - Pre-tax Amounts by Operating Segment for Stock-Based Compensation (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensationPreTaxAmountsByOperatingSegmentForStockBasedCompensationDetail</Role>
      <ShortName>Stock-Based Compensation - Pre-tax Amounts by Operating Segment for Stock-Based Compensation (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>100510 - Disclosure - Stock-Based Compensation - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetail</Role>
      <ShortName>Stock-Based Compensation - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>100520 - Disclosure - Stock-Based Compensation - Summary of Restricted Stock Units Activity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedStockUnitsActivityDetail</Role>
      <ShortName>Stock-Based Compensation - Summary of Restricted Stock Units Activity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>100530 - Disclosure - Stock-Based Compensation - Summary of Restricted Stock Units Activity (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedStockUnitsActivityParentheticalDetail</Role>
      <ShortName>Stock-Based Compensation - Summary of Restricted Stock Units Activity (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>100540 - Disclosure - Income Taxes - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetail</Role>
      <ShortName>Income Taxes - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>100550 - Disclosure - Share Repurchase Program - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureShareRepurchaseProgramAdditionalInformationDetail</Role>
      <ShortName>Share Repurchase Program - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>100560 - Disclosure - Commitments and Contingencies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetail</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>100570 - Disclosure - Segment Information - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationAdditionalInformationDetail</Role>
      <ShortName>Segment Information - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>100580 - Disclosure - Segment Information - Net Sales by Offering for North America, EMEA and APAC (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationNetSalesByOfferingForNorthAmericaEMEAAndAPACDetail</Role>
      <ShortName>Segment Information - Net Sales by Offering for North America, EMEA and APAC (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>100590 - Disclosure - Segment Information - Financial Information about Reportable Operating Segments (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationFinancialInformationAboutReportableOperatingSegmentsDetail</Role>
      <ShortName>Segment Information - Financial Information about Reportable Operating Segments (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>100600 - Disclosure - Segment Information - Summary of Total Assets by Reportable Operating Segment (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationSummaryOfTotalAssetsByReportableOperatingSegmentDetail</Role>
      <ShortName>Segment Information - Summary of Total Assets by Reportable Operating Segment (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>100610 - Disclosure - Segment Information - Pre-Tax Depreciation and Amortization by Operating Segment (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSegmentInformationPreTaxDepreciationAndAmortizationByOperatingSegmentDetail</Role>
      <ShortName>Segment Information - Pre-Tax Depreciation and Amortization by Operating Segment (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>100620 - Disclosure - Acquisitions - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitionsAdditionalInformationDetail</Role>
      <ShortName>Acquisitions - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>100630 - Disclosure - Acquisitions - Summary of Purchase Price and Estimated Fair Value of Assets Acquired and Liabilities Assumed (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitionsSummaryOfPurchasePriceAndEstimatedFairValueOfAssetsAcquiredAndLiabilitiesAssumedDetail</Role>
      <ShortName>Acquisitions - Summary of Purchase Price and Estimated Fair Value of Assets Acquired and Liabilities Assumed (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>100640 - Disclosure - Acquisitions - Summary of Pro Forma Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureAcquisitionsSummaryOfProFormaInformationDetail</Role>
      <ShortName>Acquisitions - Summary of Pro Forma Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="nsit-10q_20200331.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>100650 - Disclosure - Subsequent Event - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.insight.com/20200331/taxonomy/role/DisclosureSubsequentEventAdditionalInformationDetail</Role>
      <ShortName>Subsequent Event - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="nsit-10q_20200331.htm">nsit-10q_20200331.htm</File>
    <File>nsit-20200331.xsd</File>
    <File>nsit-20200331_cal.xml</File>
    <File>nsit-20200331_def.xml</File>
    <File>nsit-20200331_lab.xml</File>
    <File>nsit-20200331_pre.xml</File>
    <File>nsit-ex311_7.htm</File>
    <File>nsit-ex312_8.htm</File>
    <File>nsit-ex321_6.htm</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g5pjt43ojmuz000001.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
