<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>246</ContextCount>
  <ElementCount>406</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>69</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>75000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>75010 - Statement - CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_StatementCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>75020 - Statement - CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_StatementCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>75030 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_StatementCONSOLIDATEDSTATEMENTSOFOPERATIONSANDCOMPREHENSIVELOSS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>75040 - Statement - CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_StatementCONSOLIDATEDSTATEMENTSOFCHANGESINSTOCKHOLDERSEQUITY</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>75050 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_StatementCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>75060 - Disclosure - Cybersecurity Risk Management, Strategy, and Governance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureCybersecurityRiskManagementStrategyAndGovernance</Role>
      <ShortName>Cybersecurity Risk Management, Strategy, and Governance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>995457 - Disclosure - Nature of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureNatureOfBusiness</Role>
      <ShortName>Nature of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>995467 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>995477 - Disclosure - Related Party</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureRelatedParty1</Role>
      <ShortName>Related Party</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>995487 - Disclosure - Investments in Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureInvestmentsInMarketableSecurities</Role>
      <ShortName>Investments in Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>995507 - Disclosure - Other Accrued Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureOtherAccruedExpenses</Role>
      <ShortName>Other Accrued Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>995537 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>995547 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>995557 - Disclosure - Collaboration Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureCollaborationAgreements</Role>
      <ShortName>Collaboration Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995567 - Disclosure - HBV Research Agreement with Indiana University</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureHbvResearchAgreementWithIndianaUniversity</Role>
      <ShortName>HBV Research Agreement with Indiana University</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>995577 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>995587 - Disclosure - Operating Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeases</Role>
      <ShortName>Operating Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>995597 - Disclosure - Employee Benefit Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureEmployeeBenefitPlan</Role>
      <ShortName>Employee Benefit Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>995607 - Disclosure - Segment Reporting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureSegmentReporting</Role>
      <ShortName>Segment Reporting</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>995627 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995637 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsTables</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncements</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995647 - Disclosure - Investments in Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureInvestmentsInMarketableSecuritiesTables</Role>
      <ShortName>Investments in Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureInvestmentsInMarketableSecurities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>995667 - Disclosure - Other Accrued Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureOtherAccruedExpensesTables</Role>
      <ShortName>Other Accrued Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureOtherAccruedExpenses</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>995687 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockholdersEquity</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995697 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensation</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>995707 - Disclosure - Collaboration Agreements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureCollaborationAgreementsTables</Role>
      <ShortName>Collaboration Agreements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureCollaborationAgreements</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>995717 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxes</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>995727 - Disclosure - Operating Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeasesTables</Role>
      <ShortName>Operating Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeases</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995737 - Disclosure - Segment Reporting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureSegmentReportingTables</Role>
      <ShortName>Segment Reporting (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureSegmentReporting</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995747 - Disclosure - Nature of Business - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureNatureOfBusinessAdditionalInformationDetails</Role>
      <ShortName>Nature of Business - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995757 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsAdditionalInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995767 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Earnings Per Share, Basic and Diluted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsScheduleOfEarningsPerShareBasicAndDilutedDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Earnings Per Share, Basic and Diluted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995777 - Disclosure - Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAndRecentAccountingPronouncementsScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareDetails</Role>
      <ShortName>Summary of Significant Accounting Policies and Recent Accounting Pronouncements - Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995787 - Disclosure - Related Party - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureRelatedPartyAdditionalInformationDetails</Role>
      <ShortName>Related Party - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>995797 - Disclosure - Investments in Marketable Securities - Schedule of Investments in Marketable Available-for-Sale Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureInvestmentsInMarketableSecuritiesScheduleOfInvestmentsInMarketableAvailableForSaleSecuritiesDetails</Role>
      <ShortName>Investments in Marketable Securities - Schedule of Investments in Marketable Available-for-Sale Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>995807 - Disclosure - Investments in Marketable Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureInvestmentsInMarketableSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Investments in Marketable Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>995817 - Disclosure - Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureInvestmentsInMarketableSecuritiesScheduleOfFairValueOfFinancialAssetsDetails</Role>
      <ShortName>Investments in Marketable Securities - Schedule of Fair Value of Financial Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>995827 - Disclosure - Property and Equipment, Net - Schedule of Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosurePropertyAndEquipmentNetScheduleOfPropertyAndEquipmentNetDetails</Role>
      <ShortName>Property and Equipment, Net - Schedule of Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>995847 - Disclosure - Other Accrued Expenses - Schedule of Other Accrued Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureOtherAccruedExpensesScheduleOfOtherAccruedExpensesDetails</Role>
      <ShortName>Other Accrued Expenses - Schedule of Other Accrued Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>995887 - Disclosure - Stockholders' Equity - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockholdersEquityAdditionalInformationDetails</Role>
      <ShortName>Stockholders' Equity - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>995897 - Disclosure - Stockholders' Equity - Summary of Warrants and Pre-funded Warrants to Purchase Shares of Common Stock Issued and Outstanding (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureStockholdersEquitySummaryOfWarrantsAndPrefundedWarrantsToPurchaseSharesOfCommonStockIssuedAndOutstandingDetails</Role>
      <ShortName>Stockholders' Equity - Summary of Warrants and Pre-funded Warrants to Purchase Shares of Common Stock Issued and Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>995907 - Disclosure - Stockholders' Equity - Summary of Warrants and Pre-funded Warrants to Purchase Shares of Common Stock Issued and Outstanding (Parenthetical) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureStockholdersEquitySummaryOfWarrantsAndPrefundedWarrantsToPurchaseSharesOfCommonStockIssuedAndOutstandingParentheticalDetails</Role>
      <ShortName>Stockholders' Equity - Summary of Warrants and Pre-funded Warrants to Purchase Shares of Common Stock Issued and Outstanding (Parenthetical) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>995917 - Disclosure - Stock-Based Compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Stock-Based Compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>995927 - Disclosure - Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationSummaryOfStockOptionActivityAndRelatedInformationDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>995937 - Disclosure - Stock-Based Compensation - Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationSummaryOfAssumptionsUsedToEstimateFairValuesOfStockOptionsGrantsDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Assumptions Used to Estimate Fair Values of Stock Options Grants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>995947 - Disclosure - Stock-Based Compensation - Summary of Restricted Stock Units and Related Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationSummaryOfRestrictedStockUnitsAndRelatedInformationDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Restricted Stock Units and Related Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>995957 - Disclosure - Stock-Based Compensation - Summary of Performance Stock Units and Related Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureStockbasedCompensationSummaryOfPerformanceStockUnitsAndRelatedInformationDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Performance Stock Units and Related Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>995967 - Disclosure - Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureStockBasedCompensationScheduleOfRecognizedStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stock-Based Compensation - Schedule of Recognized Stock-Based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>995977 - Disclosure - Collaboration Agreements - Schedule of Changes in Contract Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureCollaborationAgreementsScheduleOfChangesInContractLiabilitiesDetails</Role>
      <ShortName>Collaboration Agreements - Schedule of Changes in Contract Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>995987 - Disclosure - Collaboration Agreements - Schedule of Collaboration Revenue Recognized with the Period (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureCollaborationAgreementsScheduleOfCollaborationRevenueRecognizedWithThePeriodDetails</Role>
      <ShortName>Collaboration Agreements - Schedule of Collaboration Revenue Recognized with the Period (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>995997 - Disclosure - Collaboration Agreements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureCollaborationAgreementsAdditionalInformationDetails</Role>
      <ShortName>Collaboration Agreements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>996007 - Disclosure - HBV Research Agreement with Indiana University - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureHbvResearchAgreementWithIndianaUniversityAdditionalInformationDetails</Role>
      <ShortName>HBV Research Agreement with Indiana University - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>996017 - Disclosure - Income Taxes - Schedule of Income Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureIncomeTaxesScheduleOfIncomeTaxExpenseDetails</Role>
      <ShortName>Income Taxes - Schedule of Income Tax Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>996027 - Disclosure - Income Taxes - Effective Income Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureIncomeTaxesEffectiveIncomeTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes - Effective Income Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>996037 - Disclosure - Income Taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income Taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>996047 - Disclosure - Income Taxes - Components of Deferred Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesComponentsOfDeferredTaxesDetails</Role>
      <ShortName>Income Taxes - Components of Deferred Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>996057 - Disclosure - Income Taxes - Summary of Net Operating Loss and Tax Credit Carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesSummaryOfNetOperatingLossAndTaxCreditCarryforwardsDetails</Role>
      <ShortName>Income Taxes - Summary of Net Operating Loss and Tax Credit Carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>996067 - Disclosure - Income Taxes - Activity Related to Gross Unrecognized Tax Benefits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesActivityRelatedToGrossUnrecognizedTaxBenefitsDetails</Role>
      <ShortName>Income Taxes - Activity Related to Gross Unrecognized Tax Benefits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>996077 - Disclosure - Operating Leases - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeasesAdditionalInformationDetails</Role>
      <ShortName>Operating Leases - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>996087 - Disclosure - Operating Leases - Schedule of Quantitative Information of Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeasesScheduleOfQuantitativeInformationOfOperatingLeasesDetails</Role>
      <ShortName>Operating Leases - Schedule of Quantitative Information of Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>996097 - Disclosure - Operating Leases - Schedule of Maturities Operating Lease Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureOperatingLeasesScheduleOfMaturitiesOperatingLeaseLiabilitiesDetails</Role>
      <ShortName>Operating Leases - Schedule of Maturities Operating Lease Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>996117 - Disclosure - Employee Benefit Plan - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/Role_DisclosureEmployeeBenefitPlanAdditionalInformationDetails</Role>
      <ShortName>Employee Benefit Plan - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>996127 - Disclosure - Segment Reporting - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureSegmentReportingAdditionalInformationDetails</Role>
      <ShortName>Segment Reporting - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="asmb-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>996137 - Disclosure - Segment Reporting - Schedule of Segment Expenses and Other Segment Items (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.assemblybio.com/20251231/taxonomy/role/DisclosureSegmentReportingScheduleOfSegmentExpensesAndOtherSegmentItemsDetails</Role>
      <ShortName>Segment Reporting - Schedule of Segment Expenses and Other Segment Items (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</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-K" isDefinitelyFs="true" isUsgaap="true" original="asmb-20251231.htm">asmb-20251231.htm</File>
    <File>asmb-20251231.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="696">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="15">http://xbrl.sec.gov/cyd/2025</BaseTaxonomy>
    <BaseTaxonomy items="40">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="5">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
