<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>201</ContextCount>
  <ElementCount>364</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>50</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Condensed Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedBalanceSheets</Role>
      <ShortName>Condensed Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Condensed Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Condensed Statements of Operations (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedStatementsOfOperationsUnaudited</Role>
      <ShortName>Condensed Statements of Operations (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedStatementsOfConvertiblePreferredStockUnitsAndStockholdersMembersEquityDeficit</Role>
      <ShortName>Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedStatementsOfConvertiblePreferredStockUnitsAndStockholdersMembersEquityDeficitParenthetical</Role>
      <ShortName>Condensed Statements of Convertible Preferred Stock/Units and Stockholders'/Members' Equity (Deficit) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - Condensed Statements of Cash Flows (unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/StatementCondensedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>Condensed Statements of Cash Flows (unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - Description of Business and Basis of Presentation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDescriptionOfBusinessAndBasisOfPresentation</Role>
      <ShortName>Description of Business and Basis of Presentation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Collaboration and License Agreement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCollaborationAndLicenseAgreement</Role>
      <ShortName>Collaboration and License Agreement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Property and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosurePropertyAndEquipment</Role>
      <ShortName>Property and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDebt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Convertible Notes</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureConvertibleNotes</Role>
      <ShortName>Convertible Notes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Stockholders' Equity (Deficit)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficit</Role>
      <ShortName>Stockholders' Equity (Deficit)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - COVID-19</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCOVID19</Role>
      <ShortName>COVID-19</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>17</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>18</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Collaboration and License Agreement (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCollaborationAndLicenseAgreementTables</Role>
      <ShortName>Collaboration and License Agreement (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCollaborationAndLicenseAgreement</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Property and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosurePropertyAndEquipmentTables</Role>
      <ShortName>Property and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosurePropertyAndEquipment</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDebt</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Stockholders' Equity (Deficit) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</Role>
      <ShortName>Stockholders' Equity (Deficit) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficit</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Description of Business and Basis of Presentation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDescriptionOfBusinessAndBasisOfPresentationAdditionalInformationDetails</Role>
      <ShortName>Description of Business and Basis of Presentation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="rna-20200930.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://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Summary of Significant Accounting Policies - Schedule of Reconciliation of Preferred Stock Warrant Liability Measured at Fair Value Using Level 3 Unobservable Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfReconciliationOfPreferredStockWarrantLiabilityMeasuredAtFairValueUsingLevel3UnobservableInputsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Reconciliation of Preferred Stock Warrant Liability Measured at Fair Value Using Level 3 Unobservable Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesScheduleOfPotentiallyDilutiveSecuritiesNotIncludedInCalculationOfDilutedNetLossPerShareDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities not Included in Calculation of Diluted Net Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Collaboration and License Agreements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCollaborationAndLicenseAgreementsAdditionalInformationDetails</Role>
      <ShortName>Collaboration and License Agreements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Collaboration and License Agreements - Reconciliation of Deferred Revenue Related to Lilly Agreement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCollaborationAndLicenseAgreementsReconciliationOfDeferredRevenueRelatedToLillyAgreementDetails</Role>
      <ShortName>Collaboration and License Agreements - Reconciliation of Deferred Revenue Related to Lilly Agreement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Property,and Equipment - Schedule of Property and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosurePropertyAndEquipmentScheduleOfPropertyAndEquipmentDetails</Role>
      <ShortName>Property,and Equipment - Schedule of Property and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Property and Equipment - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosurePropertyAndEquipmentAdditionalInformationDetails</Role>
      <ShortName>Property and Equipment - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Debt - Schedule of Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDebtScheduleOfDebtDetails</Role>
      <ShortName>Debt - Schedule of Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Debt - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureDebtAdditionalInformationDetails</Role>
      <ShortName>Debt - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Convertible Notes - Additional Information (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureConvertibleNotesAdditionalInformationDetails</Role>
      <ShortName>Convertible Notes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Commitments and Contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesAdditionalInformationDetails</Role>
      <ShortName>Commitments and Contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Commitments and Contingencies - Schedule of ROU Assets and Liabilities Related to 2014 Lease and Temporary Lease (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfROUAssetsAndLiabilitiesRelatedTo2014LeaseAndTemporaryLeaseDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of ROU Assets and Liabilities Related to 2014 Lease and Temporary Lease (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Commitments and Contingencies - Schedule of Maturities of Lease Liabilities due under 2014 Lease and Temporary Lease (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfMaturitiesOfLeaseLiabilitiesDueUnder2014LeaseAndTemporaryLeaseDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Maturities of Lease Liabilities due under 2014 Lease and Temporary Lease (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Commitments and Contingencies - Supplemental Cash Flow Information Related to Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesSupplementalCashFlowInformationRelatedToOperatingLeasesDetails</Role>
      <ShortName>Commitments and Contingencies - Supplemental Cash Flow Information Related to Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Commitments and Contingencies - Schedule of Rent Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfRentExpenseDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Rent Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Stockholders' Equity (Deficit) - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitAdditionalInformationDetails</Role>
      <ShortName>Stockholders' Equity (Deficit) - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Stockholders' Equity (Deficit) - Summary of Preferred Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitSummaryOfPreferredStockDetails</Role>
      <ShortName>Stockholders' Equity (Deficit) - Summary of Preferred Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Stockholders' Equity (Deficit) - Summary of Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitSummaryOfStockOptionActivityDetails</Role>
      <ShortName>Stockholders' Equity (Deficit) - Summary of Stock Option Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Stockholders' Equity (Deficit) - Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option/Unit Grants (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitScheduleOfAssumptionsUsedInBlackScholesOptionPricingModelToDetermineFairValueOfStockOptionUnitGrantsDetails</Role>
      <ShortName>Stockholders' Equity (Deficit) - Schedule of Assumptions Used in Black-Scholes Option Pricing Model to Determine Fair Value of Stock Option/Unit Grants (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="rna-20200930.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Stockholders' Equity (Deficit) - Schedule of Allocated Stock-based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitScheduleOfAllocatedStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stockholders' Equity (Deficit) - Schedule of Allocated Stock-based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.aviditybiosciences.com/20200930/taxonomy/role/DisclosureStockholdersEquityDeficitTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>rna-20200930.xml</File>
    <File>rna-20200930.xsd</File>
    <File>rna-20200930_cal.xml</File>
    <File>rna-20200930_def.xml</File>
    <File>rna-20200930_lab.xml</File>
    <File>rna-20200930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
