<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>128</ContextCount>
  <ElementCount>325</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>47</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementBalanceSheets</Role>
      <ShortName>Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementBalanceSheetsParenthetical</Role>
      <ShortName>Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Statements of Operations and Comprehensive Loss</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementStatementsOfOperationsAndComprehensiveLoss</Role>
      <ShortName>Statements of Operations and Comprehensive Loss</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Statements of Convertible Preferred Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementStatementsOfConvertiblePreferredStock</Role>
      <ShortName>Statements of Convertible Preferred Stock</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Statements of Stockholders' Equity (Deficit)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementStatementsOfStockholdersEquityDeficit</Role>
      <ShortName>Statements of Stockholders' Equity (Deficit)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00405 - Statement - Statements of Stockholders' Equity (Deficit) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementStatementsOfStockholdersEquityDeficitParenthetical</Role>
      <ShortName>Statements of Stockholders' Equity (Deficit) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00500 - Statement - Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/StatementStatementsOfCashFlows</Role>
      <ShortName>Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10101 - Disclosure - Organization</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureOrganization</Role>
      <ShortName>Organization</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Basis of presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureBasisOfPresentation</Role>
      <ShortName>Basis of presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Summary of significant accounting policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of significant accounting policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Research collaboration agreement with Allergan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureResearchCollaborationAgreementWithAllergan</Role>
      <ShortName>Research collaboration agreement with Allergan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Fair value measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair value measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Prepaid expenses and other current assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</Role>
      <ShortName>Prepaid expenses and other current assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Property and equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePropertyAndEquipment</Role>
      <ShortName>Property and equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Accrued expenses and other current liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</Role>
      <ShortName>Accrued expenses and other current liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Operating leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureOperatingLeases</Role>
      <ShortName>Operating leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Convertible preferred stock and stockholders??? equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquity</Role>
      <ShortName>Convertible preferred stock and stockholders??? equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Stock incentive plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlan</Role>
      <ShortName>Stock incentive plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Net loss per share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureNetLossPerShare</Role>
      <ShortName>Net loss per share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Employee benefit plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureEmployeeBenefitPlan</Role>
      <ShortName>Employee benefit plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Income taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Commitments and contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Subsequent events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSubsequentEvents</Role>
      <ShortName>Subsequent events</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>20302 - Disclosure - Summary of significant accounting policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of significant accounting policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Summary of significant accounting policiess (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciessTables</Role>
      <ShortName>Summary of significant accounting policiess (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Fair value measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair value measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Prepaid expenses and other current assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</Role>
      <ShortName>Prepaid expenses and other current assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssets</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Property and equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePropertyAndEquipmentTables</Role>
      <ShortName>Property and equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosurePropertyAndEquipment</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Accrued expenses and other current liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesTables</Role>
      <ShortName>Accrued expenses and other current liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilities</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Operating leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureOperatingLeasesTables</Role>
      <ShortName>Operating leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureOperatingLeases</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Convertible preferred stock and stockholders??? equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquityTables</Role>
      <ShortName>Convertible preferred stock and stockholders??? equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquity</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Stock incentive plan (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanTables</Role>
      <ShortName>Stock incentive plan (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureStockIncentivePlan</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Net loss per share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureNetLossPerShareTables</Role>
      <ShortName>Net loss per share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureNetLossPerShare</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Income taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Organization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureOrganizationDetails</Role>
      <ShortName>Organization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureOrganization</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Summary of significant accounting policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciesDetails</Role>
      <ShortName>Summary of significant accounting policies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciessTables</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>40302 - Disclosure - Summary of significant accounting policies - Cash, cash equivalents, and restricted cash (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciesCashCashEquivalentsAndRestrictedCashDetails</Role>
      <ShortName>Summary of significant accounting policies - Cash, cash equivalents, and restricted cash (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>40303 - Disclosure - Summary of significant accounting policies - Property and equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciesPropertyAndEquipmentDetails</Role>
      <ShortName>Summary of significant accounting policies - Property and equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>40304 - Disclosure - Summary of significant accounting policies - Income taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSummaryOfSignificantAccountingPoliciesIncomeTaxesDetails</Role>
      <ShortName>Summary of significant accounting policies - Income taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Research collaboration agreement with Allergan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureResearchCollaborationAgreementWithAllerganDetails</Role>
      <ShortName>Research collaboration agreement with Allergan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureResearchCollaborationAgreementWithAllergan</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Fair value measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureFairValueMeasurementsDetails</Role>
      <ShortName>Fair value measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureFairValueMeasurementsTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Prepaid expenses and other current assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsDetails</Role>
      <ShortName>Prepaid expenses and other current assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Property and equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosurePropertyAndEquipmentDetails</Role>
      <ShortName>Property and equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosurePropertyAndEquipmentTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Accrued expenses and other current liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesDetails</Role>
      <ShortName>Accrued expenses and other current liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureAccruedExpensesAndOtherCurrentLiabilitiesTables</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Operating leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureOperatingLeasesDetails</Role>
      <ShortName>Operating leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureOperatingLeasesTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Convertible preferred stock and stockholders??? equity - Convertible preferred stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquityConvertiblePreferredStockDetails</Role>
      <ShortName>Convertible preferred stock and stockholders??? equity - Convertible preferred stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>41002 - Disclosure - Convertible preferred stock and stockholders??? equity - Conversion update, Voting rights (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquityConversionUpdateVotingRightsDetails</Role>
      <ShortName>Convertible preferred stock and stockholders??? equity - Conversion update, Voting rights (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>41003 - Disclosure - Convertible preferred stock and stockholders??? equity - Common stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureConvertiblePreferredStockAndStockholdersEquityCommonStockDetails</Role>
      <ShortName>Convertible preferred stock and stockholders??? equity - Common stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Stock incentive plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanDetails</Role>
      <ShortName>Stock incentive plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureStockIncentivePlanTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>41102 - Disclosure - Stock incentive plan - Shares available for grant (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanSharesAvailableForGrantDetails</Role>
      <ShortName>Stock incentive plan - Shares available for grant (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>41103 - Disclosure - Stock incentive plan - Stock-based compensation expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stock incentive plan - Stock-based compensation expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>41104 - Disclosure - Stock incentive plan - Restricted stock awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanRestrictedStockAwardsDetails</Role>
      <ShortName>Stock incentive plan - Restricted stock awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>41105 - Disclosure - Stock incentive plan - Restricted stock units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanRestrictedStockUnitsDetails</Role>
      <ShortName>Stock incentive plan - Restricted stock units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>41106 - Disclosure - Stock incentive plan - Fair value assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanFairValueAssumptionsDetails</Role>
      <ShortName>Stock incentive plan - Fair value assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>41107 - Disclosure - Stock incentive plan - Activity related to stock options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanActivityRelatedToStockOptionsDetails</Role>
      <ShortName>Stock incentive plan - Activity related to stock options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>41108 - Disclosure - Stock incentive plan - Employee Stock Purchase Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureStockIncentivePlanEmployeeStockPurchasePlanDetails</Role>
      <ShortName>Stock incentive plan - Employee Stock Purchase Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Net loss per share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureNetLossPerShareDetails</Role>
      <ShortName>Net loss per share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureNetLossPerShareTables</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>41202 - Disclosure - Net loss per share - Anti-dilutive securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureNetLossPerShareAntiDilutiveSecuritiesDetails</Role>
      <ShortName>Net loss per share - Anti-dilutive securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Employee benefit plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureEmployeeBenefitPlanDetails</Role>
      <ShortName>Employee benefit plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureEmployeeBenefitPlan</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Income taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxesDetails</Role>
      <ShortName>Income taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureIncomeTaxesTables</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>41402 - Disclosure - Income taxes - Deferred tax assets and valuation allowance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxesDeferredTaxAssetsAndValuationAllowanceDetails</Role>
      <ShortName>Income taxes - Deferred tax assets and valuation allowance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>41403 - Disclosure - Income taxes - Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxesReconciliationDetails</Role>
      <ShortName>Income taxes - Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>41404 - Disclosure - Income taxes - Components of net deferred tax assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureIncomeTaxesComponentsOfNetDeferredTaxAssetsDetails</Role>
      <ShortName>Income taxes - Components of net deferred tax assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="aptx-20191231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Subsequent events (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aptinyx.com/role/DisclosureSubsequentEventsDetails</Role>
      <ShortName>Subsequent events (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aptinyx.com/role/DisclosureSubsequentEvents</ParentRole>
      <Position>65</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>aptx-20191231.xml</File>
    <File>aptx-20191231.xsd</File>
    <File>aptx-20191231_cal.xml</File>
    <File>aptx-20191231_def.xml</File>
    <File>aptx-20191231_lab.xml</File>
    <File>aptx-20191231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
