<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.8.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>151</ContextCount>
  <ElementCount>203</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>59</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Condensed Balance Sheets (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/StatementCondensedBalanceSheetsUnaudited</Role>
      <ShortName>Condensed Balance Sheets (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Condensed Balance Sheets (Parenthetical) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/StatementCondensedBalanceSheetsParentheticalUnaudited</Role>
      <ShortName>Condensed Balance Sheets (Parenthetical) (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Condensed Statements of Operations and Comprehensive Loss (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/StatementCondensedStatementsOfOperationsAndComprehensiveLossUnaudited</Role>
      <ShortName>Condensed Statements of Operations and Comprehensive Loss (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Condensed Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/StatementCondensedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Condensed Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Disclosure - Organization and Liquidity Risks</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureOrganizationAndLiquidityRisks</Role>
      <ShortName>Organization and Liquidity Risks</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Marketable Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureMarketableSecurities</Role>
      <ShortName>Marketable Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - License Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureLicenseAgreements</Role>
      <ShortName>License Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Convertible Preferred Stock and Common Stock</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureConvertiblePreferredStockAndCommonStock</Role>
      <ShortName>Convertible Preferred Stock and Common Stock</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensation</Role>
      <ShortName>Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Net Loss per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShare</Role>
      <ShortName>Net Loss per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>16</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>17</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>18</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Marketable Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureMarketableSecuritiesTables</Role>
      <ShortName>Marketable Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureMarketableSecurities</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Convertible Preferred Stock and Common Stock (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureConvertiblePreferredStockAndCommonStockTables</Role>
      <ShortName>Convertible Preferred Stock and Common Stock (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureConvertiblePreferredStockAndCommonStock</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensationTables</Role>
      <ShortName>Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensation</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Net Loss per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShareTables</Role>
      <ShortName>Net Loss per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShare</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Organization - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureOrganizationAdditionalInformationDetails</Role>
      <ShortName>Organization - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/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>26</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Fair Value Measurements - Summary of Financial Assets Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureFairValueMeasurementsSummaryOfFinancialAssetsSubjectToFairValueMeasurementsOnRecurringBasisAndLevelOfInputsUsedInMeasurementsDetails</Role>
      <ShortName>Fair Value Measurements - Summary of Financial Assets Subject to Fair Value Measurements on Recurring Basis and Level of Inputs Used in Measurements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Fair Value Measurements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureFairValueMeasurementsAdditionalInformationDetails</Role>
      <ShortName>Fair Value Measurements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Marketable Securities - Summary of Marketable Securities Classified as Available-for-Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureMarketableSecuritiesSummaryOfMarketableSecuritiesClassifiedAsAvailableForSaleDetails</Role>
      <ShortName>Marketable Securities - Summary of Marketable Securities Classified as Available-for-Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Marketable Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureMarketableSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Marketable Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - License Agreements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureLicenseAgreementsAdditionalInformationDetails</Role>
      <ShortName>License Agreements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Commitments and Contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Commitments and Contingencies - Summary of Future Minimum Lease Payments under Non-cancellable Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureCommitmentsAndContingenciesSummaryOfFutureMinimumLeasePaymentsUnderNonCancellableOperatingLeasesDetails</Role>
      <ShortName>Commitments and Contingencies - Summary of Future Minimum Lease Payments under Non-cancellable Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Related-Party Transactions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>Related-Party Transactions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Convertible Preferred Stock and Common Stock - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureConvertiblePreferredStockAndCommonStockAdditionalInformationDetails</Role>
      <ShortName>Convertible Preferred Stock and Common Stock - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Convertible Preferred Stock and Common Stock - Summary of Convertible Preferred Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureConvertiblePreferredStockAndCommonStockSummaryOfConvertiblePreferredStockDetails</Role>
      <ShortName>Convertible Preferred Stock and Common Stock - Summary of Convertible Preferred Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Stock-Based Compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Stock-Based Compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Stock-Based Compensation - Summary of Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockOptionActivityDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Stock Option Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Stock-Based Compensation - Summary of Restricted Stock Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfRestrictedStockActivityDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Restricted Stock Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureStockBasedCompensationSummaryOfStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stock-Based Compensation - Summary of Stock-based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Net Loss per Common Share - Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShareScheduleOfReconciliationOfNumeratorsAndDenominatorsUsedInComputingNetLossFromContinuingOperationsPerShareDetails</Role>
      <ShortName>Net Loss per Common Share - Schedule of Reconciliation of Numerators and Denominators Used In Computing Net Loss From Continuing Operations Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Net Loss per Common Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShareSummaryOfPotentiallyDilutiveSecuritiesExcludedFromComputationOfDilutedPerShareDetails</Role>
      <ShortName>Net Loss per Common Share - Summary of Potentially Dilutive Securities Excluded from Computation of Diluted Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="ubx-20180331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Net Loss per Common Share - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://unitybiotechnology.com/20180331/taxonomy/role/DisclosureNetLossPerCommonShareAdditionalInformationDetails</Role>
      <ShortName>Net Loss per Common Share - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>ubx-20180331.xml</File>
    <File>ubx-20180331.xsd</File>
    <File>ubx-20180331_cal.xml</File>
    <File>ubx-20180331_def.xml</File>
    <File>ubx-20180331_lab.xml</File>
    <File>ubx-20180331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2017-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/invest/2013-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2014-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
