<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.19.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>164</ContextCount>
  <ElementCount>329</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>32</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedStatementsOfIncomeAndComprehensiveIncomeUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF INCOME AND COMPREHENSIVE INCOME (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002000 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002501 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1004000 - Statement - CONDENSED CONSOLIDATED STATEMENT OF EQUITY (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedStatementOfEquityUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENT OF EQUITY (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004001 - Statement - CONDENSED CONSOLIDATED STATEMENT OF EQUITY (UNAUDITED) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/CondensedConsolidatedStatementOfEquityUnauditedParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENT OF EQUITY (UNAUDITED) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Interim financial statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InterimFinancialStatements</Role>
      <ShortName>Interim financial statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Revenues</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/Revenues</Role>
      <ShortName>Revenues</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Investments in debt and equity securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecurities</Role>
      <ShortName>Investments in debt and equity securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Fair value measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/FairValueMeasurements</Role>
      <ShortName>Fair value measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Investment and other gains - net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNet</Role>
      <ShortName>Investment and other gains - net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Estimated title losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EstimatedTitleLosses</Role>
      <ShortName>Estimated title losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Share-based payments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/ShareBasedPayments</Role>
      <ShortName>Share-based payments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2118100 - Disclosure - Earnings per share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EarningsPerShare</Role>
      <ShortName>Earnings per share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2119100 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2121100 - Disclosure - Contingent liabilities and commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/ContingentLiabilitiesAndCommitments</Role>
      <ShortName>Contingent liabilities and commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2122100 - Disclosure - Regulatory and legal developments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/RegulatoryAndLegalDevelopments</Role>
      <ShortName>Regulatory and legal developments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Segment information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/SegmentInformation</Role>
      <ShortName>Segment information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2124100 - Disclosure - Other comprehensive (loss) income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/OtherComprehensiveLossIncome</Role>
      <ShortName>Other comprehensive (loss) income</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2201201 - Disclosure - Interim financial statements (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InterimFinancialStatementsPolicies</Role>
      <ShortName>Interim financial statements (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2302301 - Disclosure - Revenues (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/RevenuesTables</Role>
      <ShortName>Revenues (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/Revenues</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Investments in debt and equity securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesTables</Role>
      <ShortName>Investments in debt and equity securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecurities</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Fair value measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair value measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/FairValueMeasurements</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Investment and other gains - net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNetTables</Role>
      <ShortName>Investment and other gains - net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/InvestmentAndOtherGainsNet</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Estimated title losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EstimatedTitleLossesTables</Role>
      <ShortName>Estimated title losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/EstimatedTitleLosses</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2318301 - Disclosure - Earnings per share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EarningsPerShareTables</Role>
      <ShortName>Earnings per share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/EarningsPerShare</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2319301 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/Leases</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2323301 - Disclosure - Segment information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/SegmentInformationTables</Role>
      <ShortName>Segment information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/SegmentInformation</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2324301 - Disclosure - Other comprehensive (loss) income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/OtherComprehensiveLossIncomeTables</Role>
      <ShortName>Other comprehensive (loss) income (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.stewart.com/role/OtherComprehensiveLossIncome</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2401402 - Disclosure - Interim financial statements - Restrictions on Cash and Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InterimFinancialStatementsRestrictionsOnCashAndInvestmentsDetails</Role>
      <ShortName>Interim financial statements - Restrictions on Cash and Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2401403 - Disclosure - Interim financial statements - Recently Adopted Accounting Standard (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InterimFinancialStatementsRecentlyAdoptedAccountingStandardDetails</Role>
      <ShortName>Interim financial statements - Recently Adopted Accounting Standard (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2401404 - Disclosure - Interim financial statements - Merger Agreement Termination (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InterimFinancialStatementsMergerAgreementTerminationDetails</Role>
      <ShortName>Interim financial statements - Merger Agreement Termination (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2402402 - Disclosure - Revenues (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/RevenuesDetails</Role>
      <ShortName>Revenues (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/RevenuesTables</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Investments in debt and equity securities - Investments in Debt and Equity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesInvestmentsInDebtAndEquitySecuritiesDetails</Role>
      <ShortName>Investments in debt and equity securities - Investments in Debt and Equity Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Investments in debt and equity securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesAdditionalInformationDetails</Role>
      <ShortName>Investments in debt and equity securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2407404 - Disclosure - Investments in debt and equity securities - Amortized Costs and Fair Values (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesAmortizedCostsAndFairValuesDetails</Role>
      <ShortName>Investments in debt and equity securities - Amortized Costs and Fair Values (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2407405 - Disclosure - Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesGrossUnrealizedGainsAndLossesDetails</Role>
      <ShortName>Investments in debt and equity securities - Gross Unrealized Gains and Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2407406 - Disclosure - Investments in debt and equity securities - Debt Securities According to Contractual Terms (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesDebtSecuritiesAccordingToContractualTermsDetails</Role>
      <ShortName>Investments in debt and equity securities - Debt Securities According to Contractual Terms (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2407407 - Disclosure - Investments in debt and equity securities - Gross Unrealized Losses on Investments and Fair Values of Related Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentsInDebtAndEquitySecuritiesGrossUnrealizedLossesOnInvestmentsAndFairValuesOfRelatedSecuritiesDetails</Role>
      <ShortName>Investments in debt and equity securities - Gross Unrealized Losses on Investments and Fair Values of Related Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Fair value measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/FairValueMeasurementsDetails</Role>
      <ShortName>Fair value measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/FairValueMeasurementsTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Investment and other gains - net - Gross Realized Investment and Other Gains and Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNetGrossRealizedInvestmentAndOtherGainsAndLossesDetails</Role>
      <ShortName>Investment and other gains - net - Gross Realized Investment and Other Gains and Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2412403 - Disclosure - Investment and other gains - net - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNetAdditionalInformationDetails</Role>
      <ShortName>Investment and other gains - net - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2412404 - Disclosure - Investment and other gains - net - Net Gains on Investments in Equity Securities Still Held (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNetNetGainsOnInvestmentsInEquitySecuritiesStillHeldDetails</Role>
      <ShortName>Investment and other gains - net - Net Gains on Investments in Equity Securities Still Held (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2412405 - Disclosure - Investment and other gains - net - Proceeds from the Sale of Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/InvestmentAndOtherGainsNetProceedsFromSaleOfInvestmentsDetails</Role>
      <ShortName>Investment and other gains - net - Proceeds from the Sale of Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Estimated title losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EstimatedTitleLossesDetails</Role>
      <ShortName>Estimated title losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/EstimatedTitleLossesTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2415401 - Disclosure - Share-based payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/ShareBasedPaymentsDetails</Role>
      <ShortName>Share-based payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/ShareBasedPayments</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2418402 - Disclosure - Earnings per share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/EarningsPerShareDetails</Role>
      <ShortName>Earnings per share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/EarningsPerShareTables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2419402 - Disclosure - Leases - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/LeasesAdditionalInformationDetails</Role>
      <ShortName>Leases - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2419403 - Disclosure - Leases - Classification of Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/LeasesClassificationOfLeasesDetails</Role>
      <ShortName>Leases - Classification of Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2419404 - Disclosure - Leases - Other Information Related to Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/LeasesOtherInformationRelatedToLeasesDetails</Role>
      <ShortName>Leases - Other Information Related to Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2419405 - Disclosure - Leases - Future Minimum Lease Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/LeasesFutureMinimumLeasePaymentsDetails</Role>
      <ShortName>Leases - Future Minimum Lease Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2421401 - Disclosure - Contingent liabilities and commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/ContingentLiabilitiesAndCommitmentsDetails</Role>
      <ShortName>Contingent liabilities and commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/ContingentLiabilitiesAndCommitments</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2423402 - Disclosure - Segment information - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/SegmentInformationAdditionalInformationDetails</Role>
      <ShortName>Segment information - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2423403 - Disclosure - Segment information - Selected Statement of Operations and Income (Loss) Information Related to Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/SegmentInformationSelectedStatementOfOperationsAndIncomeLossInformationRelatedToSegmentsDetails</Role>
      <ShortName>Segment information - Selected Statement of Operations and Income (Loss) Information Related to Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2423404 - Disclosure - Segment information - Revenues Generated in United States and All International Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/SegmentInformationRevenuesGeneratedInUnitedStatesAndAllInternationalOperationsDetails</Role>
      <ShortName>Segment information - Revenues Generated in United States and All International Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2424402 - Disclosure - Other comprehensive (loss) income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.stewart.com/role/OtherComprehensiveLossIncomeDetails</Role>
      <ShortName>Other comprehensive (loss) income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.stewart.com/role/OtherComprehensiveLossIncomeTables</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="q3-2019stewart10xq.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items - q3-2019stewart10xq.htm</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/role/uncategorizedFacts</Role>
      <ShortName>Uncategorized Items - q3-2019stewart10xq.htm</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>58</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="q3-2019stewart10xq.htm">q3-2019stewart10xq.htm</File>
    <File>q3-19ex311.htm</File>
    <File>q3-19ex312.htm</File>
    <File>q3-19ex321.htm</File>
    <File>q3-19ex322.htm</File>
    <File>stc-20190930.xsd</File>
    <File>stc-20190930_cal.xml</File>
    <File>stc-20190930_def.xml</File>
    <File>stc-20190930_lab.xml</File>
    <File>stc-20190930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2017-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
