<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.4</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>139</ContextCount>
  <ElementCount>327</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>49</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>5</UnitCount>
  <MyReports>
    <Report instance="sybx-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.synlogictx.com/20251231/taxonomy/role/Role_DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="sybx-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.synlogictx.com/20251231/taxonomy/role/Role_StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="sybx-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.synlogictx.com/20251231/taxonomy/role/Role_StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="sybx-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.synlogictx.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="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>75040 - Statement - Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_StatementConsolidatedStatementsOfStockholdersEquity</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="sybx-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.synlogictx.com/20251231/taxonomy/role/Role_StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.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>7</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.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>8</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>995455 - Disclosure - Cybersecurity Risk Management, Strategy, and Governance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureCybersecurityRiskManagementStrategyAndGovernance</Role>
      <ShortName>Cybersecurity Risk Management, Strategy, and Governance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>995465 - Disclosure - Nature of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNatureOfBusiness</Role>
      <ShortName>Nature of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>995475 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>995485 - Disclosure - Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstruments</Role>
      <ShortName>Fair Value of Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>995505 - Disclosure - Assets Held for Sale, Property and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureAssetsHeldForSalePropertyAndEquipment</Role>
      <ShortName>Assets Held for Sale, Property and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>995515 - Disclosure - Prepaid Expenses and Other Current Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosurePrepaidExpensesAndOtherCurrentAssets</Role>
      <ShortName>Prepaid Expenses and Other Current Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>995525 - Disclosure - Accrued Expenses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureAccruedExpenses</Role>
      <ShortName>Accrued Expenses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>995535 - Disclosure - Restructuring and Other Charges</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureRestructuringAndOtherCharges</Role>
      <ShortName>Restructuring and Other Charges</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>995545 - Disclosure - Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureStockholdersEquity</Role>
      <ShortName>Stockholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>995555 - Disclosure - Equity-based Compensation and Equity Incentive Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlans</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995575 - Disclosure - Net Loss per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNetLossPerShare</Role>
      <ShortName>Net Loss per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>995585 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>995615 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>995625 - Disclosure - Employee Benefits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEmployeeBenefits</Role>
      <ShortName>Employee Benefits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>995645 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>995665 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995685 - Disclosure - Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsTables</Role>
      <ShortName>Fair Value of Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstruments</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995705 - Disclosure - Assets Held for Sale, Property and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureAssetsHeldForSalePropertyAndEquipmentTables</Role>
      <ShortName>Assets Held for Sale, Property and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureAssetsHeldForSalePropertyAndEquipment</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>995715 - Disclosure - Prepaid Expenses and Other Current Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</Role>
      <ShortName>Prepaid Expenses and Other Current Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosurePrepaidExpensesAndOtherCurrentAssets</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>995725 - Disclosure - Accrued Expenses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureAccruedExpensesTables</Role>
      <ShortName>Accrued Expenses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureAccruedExpenses</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995735 - Disclosure - Stockholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureStockholdersEquityTables</Role>
      <ShortName>Stockholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureStockholdersEquity</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>995745 - Disclosure - Equity-based Compensation and Equity Incentive Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansTables</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlans</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>995755 - Disclosure - Net Loss per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNetLossPerShareTables</Role>
      <ShortName>Net Loss per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNetLossPerShare</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>995765 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxes</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995785 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformation</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995795 - Disclosure - Nature of Business - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNatureOfBusinessAdditionalInformationDetail</Role>
      <ShortName>Nature of Business - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995805 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetail</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995815 - Disclosure - Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfReconciliationOfCashCashEquivalentsAndRestrictedCashDetail</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995835 - Disclosure - Fair Value of Financial Instruments - Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureFairValueOfFinancialInstrumentsScheduleOfCompanySClassifiedAssetsMeasuredAtFairValueOnRecurringBasisDetail</Role>
      <ShortName>Fair Value of Financial Instruments - Schedule of Company's Classified Assets Measured at Fair Value on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995845 - Disclosure - Fair Value of Financial Instruments - Schedule of Assumptions Used in Determining Fair Value of Warrants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsScheduleOfAssumptionsUsedInDeterminingFairValueOfWarrantsDetails</Role>
      <ShortName>Fair Value of Financial Instruments - Schedule of Assumptions Used in Determining Fair Value of Warrants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>995855 - Disclosure - Assets Held for Sale, Property and Equipment - Summary of Assets Held for Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureAssetsHeldForSalePropertyAndEquipmentSummaryOfAssetsHeldForSaleDetails</Role>
      <ShortName>Assets Held for Sale, Property and Equipment - Summary of Assets Held for Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>995865 - Disclosure - Assets Held for Sale, Property and Equipment - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureAssetsHeldForSalePropertyAndEquipmentAdditionalInformationDetail</Role>
      <ShortName>Assets Held for Sale, Property and Equipment - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>995875 - Disclosure - Prepaid Expenses and Other Current Assets (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosurePrepaidExpensesAndOtherCurrentAssetsDetail</Role>
      <ShortName>Prepaid Expenses and Other Current Assets (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosurePrepaidExpensesAndOtherCurrentAssetsTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>995885 - Disclosure - Accrued Expenses - Schedule of Accrued Expenses (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureAccruedExpensesScheduleOfAccruedExpensesDetail</Role>
      <ShortName>Accrued Expenses - Schedule of Accrued Expenses (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>995895 - Disclosure - Restructuring and Other Charges (Additional Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureRestructuringAndOtherChargesAdditionalInformationDetails</Role>
      <ShortName>Restructuring and Other Charges (Additional Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureRestructuringAndOtherCharges</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>995905 - Disclosure - Stockholders' Equity - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureStockholdersEquityAdditionalInformationDetail</Role>
      <ShortName>Stockholders' Equity - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>995925 - Disclosure - Stockholders' Equity - Schedule of Shares of Common Stock Reserved for Future Issuance (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureStockholdersEquityScheduleOfSharesOfCommonStockReservedForFutureIssuanceDetail</Role>
      <ShortName>Stockholders' Equity - Schedule of Shares of Common Stock Reserved for Future Issuance (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>995935 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansAdditionalInformationDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>995945 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Weighted Average Assumption Used Black-Scholes Option-pricing Model for Stock Options Issued to Employees and Non-employees (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfWeightedAverageAssumptionUsedBlackScholesOptionPricingModelForStockOptionsIssuedToEmployeesAndNonEmployeesDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Weighted Average Assumption Used Black-Scholes Option-pricing Model for Stock Options Issued to Employees and Non-employees (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>995955 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 and 2017 Plan (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfStockOptionActivityUnder2015And2017PlanDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 and 2017 Plan (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>995965 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 and 2017 Plan (Parenthetical) (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfStockOptionActivityUnder2015And2017PlanParentheticalDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Stock Option Activity Under 2015 and 2017 Plan (Parenthetical) (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>995975 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Restricted Common Stock Activity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfRestrictedCommonStockActivityDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Restricted Common Stock Activity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>995985 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfEquityBasedCompensationExpensesDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>995995 - Disclosure - Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses by Award Type (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEquityBasedCompensationAndEquityIncentivePlansScheduleOfEquityBasedCompensationExpensesByAwardTypeDetail</Role>
      <ShortName>Equity-based Compensation and Equity Incentive Plans - Schedule of Equity-based Compensation Expenses by Award Type (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>996005 - Disclosure - Collaboration Agreements - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureCollaborationAgreementsAdditionalInformationDetail</Role>
      <ShortName>Collaboration Agreements - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>996015 - Disclosure - Net Loss per Share - Schedule of Computation of Basic and Diluted Net Loss per Share (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNetLossPerShareScheduleOfComputationOfBasicAndDilutedNetLossPerShareDetail</Role>
      <ShortName>Net Loss per Share - Schedule of Computation of Basic and Diluted Net Loss per Share (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>996025 - Disclosure - Net Loss per Share - Schedule of Potentially Common Shares Excluded from Calculation of Net Loss Per share (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureNetLossPerShareScheduleOfPotentiallyCommonSharesExcludedFromCalculationOfNetLossPerShareDetail</Role>
      <ShortName>Net Loss per Share - Schedule of Potentially Common Shares Excluded from Calculation of Net Loss Per share (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>996035 - Disclosure - Income Taxes - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesAdditionalInformationDetail</Role>
      <ShortName>Income Taxes - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>996045 - Disclosure - Income Taxes - Schedule of Temporary Differences Between Basis of Deferred Tax Assets and Liabilities (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesScheduleOfTemporaryDifferencesBetweenBasisOfDeferredTaxAssetsAndLiabilitiesDetail</Role>
      <ShortName>Income Taxes - Schedule of Temporary Differences Between Basis of Deferred Tax Assets and Liabilities (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>996055 - Disclosure - Income Taxes - Schedule of Effective Income Tax Rate With Tax Amount (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureIncomeTaxesScheduleOfEffectiveIncomeTaxRateWithTaxAmountDetails</Role>
      <ShortName>Income Taxes - Schedule of Effective Income Tax Rate With Tax Amount (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>996065 - Disclosure - Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Company's Effective Income Tax Rate (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesReconciliationOfStatutoryFederalIncomeTaxRateToCompanySEffectiveIncomeTaxRateDetail</Role>
      <ShortName>Income Taxes - Reconciliation of Statutory Federal Income Tax Rate to Company's Effective Income Tax Rate (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>996075 - Disclosure - Income Taxes - Summary of Net Income Tax Paid of Refund Received (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureIncomeTaxesSummaryOfNetIncomeTaxPaidOfRefundReceivedDetails</Role>
      <ShortName>Income Taxes - Summary of Net Income Tax Paid of Refund Received (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>996085 - Disclosure - Income Taxes - Schedule of Valuation Allowance - (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureIncomeTaxesScheduleOfValuationAllowanceDetail</Role>
      <ShortName>Income Taxes - Schedule of Valuation Allowance - (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>996105 - Disclosure - Leases - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureLeasesAdditionalInformationDetail</Role>
      <ShortName>Leases - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>996155 - Disclosure - Employee Benefits - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureEmployeeBenefitsAdditionalInformationDetail</Role>
      <ShortName>Employee Benefits - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>996165 - Disclosure - Related-Party Transactions - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/Role_DisclosureRelatedPartyTransactionsAdditionalInformationDetail</Role>
      <ShortName>Related-Party Transactions - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>996175 - Disclosure - Segment Information - Summary of Research and Development, General and Administrative Expenses, and Restructuring Charges are Significant Segment Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformationSummaryOfResearchAndDevelopmentGeneralAndAdministrativeExpensesAndRestructuringChargesAreSignificantSegmentExpen</Role>
      <ShortName>Segment Information - Summary of Research and Development, General and Administrative Expenses, and Restructuring Charges are Significant Segment Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="sybx-20251231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>996185 - Disclosure - Segment Information (Additional Information) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformationAdditionalInformationDetails</Role>
      <ShortName>Segment Information (Additional Information) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.synlogictx.com/20251231/taxonomy/role/DisclosureSegmentInformationTables</ParentRole>
      <Position>66</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="sybx-20251231.htm">sybx-20251231.htm</File>
    <File>sybx-20251231.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="501">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="14">http://xbrl.sec.gov/cyd/2025</BaseTaxonomy>
    <BaseTaxonomy items="38">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
