<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>270</ContextCount>
  <ElementCount>468</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>111</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>13</UnitCount>
  <MyReports>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/DocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1001501 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1002000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedStatementsOfOperations</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1003000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedStatementsOfEquity</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1003001 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedStatementsOfEquityParentheticals</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF EQUITY (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1004000 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Organization and Description of Business</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OrganizationAndDescriptionOfBusiness</Role>
      <ShortName>Organization and Description of Business</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2102100 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Real Estate Investments, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNet</Role>
      <ShortName>Real Estate Investments, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Identified Intangible Assets, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsNet</Role>
      <ShortName>Identified Intangible Assets, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2106100 - Disclosure - Other Assets, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OtherAssetsNet</Role>
      <ShortName>Other Assets, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2107100 - Disclosure - Mortgage Loans Payable, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/MortgageLoansPayableNet</Role>
      <ShortName>Mortgage Loans Payable, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2108100 - Disclosure - Line of Credit and Term Loan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LineOfCreditAndTermLoan</Role>
      <ShortName>Line of Credit and Term Loan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Derivative Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/DerivativeFinancialInstruments</Role>
      <ShortName>Derivative Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Identified Intangible Liabilities, Net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleLiabilitiesNet</Role>
      <ShortName>Identified Intangible Liabilities, Net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/CommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Redeemable Noncontrolling Interests</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RedeemableNoncontrollingInterests</Role>
      <ShortName>Redeemable Noncontrolling Interests</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/Equity</Role>
      <ShortName>Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2116100 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2117100 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2120100 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2123100 - Disclosure - Segment Reporting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SegmentReporting</Role>
      <ShortName>Segment Reporting</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2125100 - Disclosure - Concentration of Credit Risk</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/ConcentrationOfCreditRisk</Role>
      <ShortName>Concentration of Credit Risk</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2126100 - Disclosure - Per Share Data</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/PerShareData</Role>
      <ShortName>Per Share Data</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2302302 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Real Estate Investments, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNetTables</Role>
      <ShortName>Real Estate Investments, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/RealEstateInvestmentsNet</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Identified Intangible Assets, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsNetTables</Role>
      <ShortName>Identified Intangible Assets, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsNet</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Other Assets, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OtherAssetsNetTables</Role>
      <ShortName>Other Assets, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/OtherAssetsNet</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2307301 - Disclosure - Mortgage Loans Payable, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/MortgageLoansPayableNetTables</Role>
      <ShortName>Mortgage Loans Payable, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/MortgageLoansPayableNet</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Derivative Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/DerivativeFinancialInstrumentsTables</Role>
      <ShortName>Derivative Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/DerivativeFinancialInstruments</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Identified Intangible Liabilities, Net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleLiabilitiesNetTables</Role>
      <ShortName>Identified Intangible Liabilities, Net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/IdentifiedIntangibleLiabilitiesNet</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Redeemable Noncontrolling Interests (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RedeemableNoncontrollingInterestsTables</Role>
      <ShortName>Redeemable Noncontrolling Interests (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/RedeemableNoncontrollingInterests</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/EquityTables</Role>
      <ShortName>Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/Equity</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2315301 - Disclosure - Related Party Transactions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RelatedPartyTransactionsTables</Role>
      <ShortName>Related Party Transactions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/RelatedPartyTransactions</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2316301 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/FairValueMeasurements</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2317301 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/IncomeTaxes</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2320301 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/Leases</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2323301 - Disclosure - Segment Reporting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SegmentReportingTables</Role>
      <ShortName>Segment Reporting (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/SegmentReporting</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2325301 - Disclosure - Concentration of Credit Risk (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/ConcentrationOfCreditRiskTables</Role>
      <ShortName>Concentration of Credit Risk (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/ConcentrationOfCreditRisk</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2401401 - Disclosure - Organization and Description of Business (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OrganizationAndDescriptionOfBusinessDetail</Role>
      <ShortName>Organization and Description of Business (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/OrganizationAndDescriptionOfBusiness</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2402403 - Disclosure - Summary of Accounting Policies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfAccountingPoliciesDetails</Role>
      <ShortName>Summary of Accounting Policies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2402404 - Disclosure - Summary of Significant Accounting Policies Disaggregation of Revenues (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPoliciesDisaggregationOfRevenuesDetails</Role>
      <ShortName>Summary of Significant Accounting Policies Disaggregation of Revenues (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2402405 - Disclosure - Summary of Significant Accounting Policies Accounts Receivable and Deferred Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SummaryOfSignificantAccountingPoliciesAccountsReceivableAndDeferredRevenueDetails</Role>
      <ShortName>Summary of Significant Accounting Policies Accounts Receivable and Deferred Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Real Estate Investments, Net - Investments in Consolidated Properties (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNetInvestmentsInConsolidatedPropertiesDetail</Role>
      <ShortName>Real Estate Investments, Net - Investments in Consolidated Properties (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2403403 - Disclosure - Real Estate Investments, Net - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNetAdditionalInformationDetail</Role>
      <ShortName>Real Estate Investments, Net - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2403404 - Disclosure - Real Estate Investments, Net - Summary of Acquisitions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNetSummaryOfAcquisitionsDetails</Role>
      <ShortName>Real Estate Investments, Net - Summary of Acquisitions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2403405 - Disclosure - Real Estate Investments, Net  - Assets and Liabilities Acquired (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RealEstateInvestmentsNetAssetsAndLiabilitiesAcquiredDetails</Role>
      <ShortName>Real Estate Investments, Net  - Assets and Liabilities Acquired (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Identified Intangible Assets - Summary of Identified Intangibles (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsSummaryOfIdentifiedIntangiblesDetail</Role>
      <ShortName>Identified Intangible Assets - Summary of Identified Intangibles (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2405403 - Disclosure - Identified Intangible Assets - Summary of Amortization Expense on Identified Intangible Assets, Net (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsSummaryOfAmortizationExpenseOnIdentifiedIntangibleAssetsNetDetail</Role>
      <ShortName>Identified Intangible Assets - Summary of Amortization Expense on Identified Intangible Assets, Net (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2405404 - Disclosure - Identified Intangible Assets, Net Identified Intangible Assets, Net (Phantom) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleAssetsNetIdentifiedIntangibleAssetsNetPhantomDetails</Role>
      <ShortName>Identified Intangible Assets, Net Identified Intangible Assets, Net (Phantom) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2406402 - Disclosure - Other Assets, Net - Other Assets, Net (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OtherAssetsNetOtherAssetsNetDetail</Role>
      <ShortName>Other Assets, Net - Other Assets, Net (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2406403 - Disclosure - Other Assets, Net - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OtherAssetsNetAdditionalInformationDetail</Role>
      <ShortName>Other Assets, Net - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2406404 - Disclosure - Other Assets, Net Other Assets, Net (Phantom) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/OtherAssetsNetOtherAssetsNetPhantomDetails</Role>
      <ShortName>Other Assets, Net Other Assets, Net (Phantom) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2407402 - Disclosure - Mortgage Loans Payable, Net - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/MortgageLoansPayableNetAdditionalInformationDetail</Role>
      <ShortName>Mortgage Loans Payable, Net - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Mortgage Loans Payable, Net - Mortgage Loans Payable (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/MortgageLoansPayableNetMortgageLoansPayableDetail</Role>
      <ShortName>Mortgage Loans Payable, Net - Mortgage Loans Payable (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2407404 - Disclosure - Mortgage Loans Payable - Principal Payments Due on Mortgage Loans Payable (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/MortgageLoansPayablePrincipalPaymentsDueOnMortgageLoansPayableDetail</Role>
      <ShortName>Mortgage Loans Payable - Principal Payments Due on Mortgage Loans Payable (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2408401 - Disclosure - Line of Credit and Term Loan (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LineOfCreditAndTermLoanDetail</Role>
      <ShortName>Line of Credit and Term Loan (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/LineOfCreditAndTermLoan</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Derivative Financial Instruments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/DerivativeFinancialInstrumentsAdditionalInformationDetails</Role>
      <ShortName>Derivative Financial Instruments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Derivative Financial Instruments (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/DerivativeFinancialInstrumentsDetail</Role>
      <ShortName>Derivative Financial Instruments (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/DerivativeFinancialInstrumentsTables</ParentRole>
      <Position>62</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Identified Intangible Liabilities, Net - Summary of Amortization Expense on Below Market Leases (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleLiabilitiesNetSummaryOfAmortizationExpenseOnBelowMarketLeasesDetail</Role>
      <ShortName>Identified Intangible Liabilities, Net - Summary of Amortization Expense on Below Market Leases (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2411403 - Disclosure - Identified Intangible Liabilities, Net Identified Intangible Liabilities, Net - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IdentifiedIntangibleLiabilitiesNetIdentifiedIntangibleLiabilitiesNetAdditionalInformationDetails</Role>
      <ShortName>Identified Intangible Liabilities, Net Identified Intangible Liabilities, Net - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Redeemable Noncontrolling Interests (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RedeemableNoncontrollingInterestsDetails</Role>
      <ShortName>Redeemable Noncontrolling Interests (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/RedeemableNoncontrollingInterestsTables</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Redeemable Noncontrolling Interests Redeemable Noncontrolling Interest (Phantom) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RedeemableNoncontrollingInterestsRedeemableNoncontrollingInterestPhantomDetails</Role>
      <ShortName>Redeemable Noncontrolling Interests Redeemable Noncontrolling Interest (Phantom) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Equity (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/EquityDetail</Role>
      <ShortName>Equity (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/EquityTables</ParentRole>
      <Position>67</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2414403 - Disclosure - Equity Phantom (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/EquityPhantomDetails</Role>
      <ShortName>Equity Phantom (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2415402 - Disclosure - Related Party Transactions - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RelatedPartyTransactionsAdditionalInformationDetail</Role>
      <ShortName>Related Party Transactions - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2415403 - Disclosure - Related Party Transactions - Related Party Description (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RelatedPartyTransactionsRelatedPartyDescriptionDetail</Role>
      <ShortName>Related Party Transactions - Related Party Description (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2415404 - Disclosure - Related Party Transactions - Schedule of Amount Outstanding to Affiliates (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/RelatedPartyTransactionsScheduleOfAmountOutstandingToAffiliatesDetail</Role>
      <ShortName>Related Party Transactions - Schedule of Amount Outstanding to Affiliates (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2416402 - Disclosure - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/FairValueMeasurementsAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetail</Role>
      <ShortName>Fair Value Measurements - Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2416403 - Disclosure - Fair Value Measurements Fair Value by Balance Sheet Grouping (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/FairValueMeasurementsFairValueByBalanceSheetGroupingDetails</Role>
      <ShortName>Fair Value Measurements Fair Value by Balance Sheet Grouping (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2417402 - Disclosure - Income Taxes - Income Tax Expense (Benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/IncomeTaxesIncomeTaxExpenseBenefitDetails</Role>
      <ShortName>Income Taxes - Income Tax Expense (Benefit) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2420402 - Disclosure - Leases Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesAdditionalInformationDetails</Role>
      <ShortName>Leases Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2420403 - Disclosure - Leases Lessor, Future Minimum Rents Due (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesLessorFutureMinimumRentsDueDetails</Role>
      <ShortName>Leases Lessor, Future Minimum Rents Due (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2420404 - Disclosure - Leases Components of Lease Cost (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesComponentsOfLeaseCostDetails</Role>
      <ShortName>Leases Components of Lease Cost (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2420405 - Disclosure - Leases Lease Term and Discount Rate (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesLeaseTermAndDiscountRateDetails</Role>
      <ShortName>Leases Lease Term and Discount Rate (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>2420406 - Disclosure - Leases Future Minimum Rent Payments, Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/LeasesFutureMinimumRentPaymentsOperatingLeasesDetails</Role>
      <ShortName>Leases Future Minimum Rent Payments, Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>2423402 - Disclosure - Segment Reporting - Summary Information for Reportable Segments (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/SegmentReportingSummaryInformationForReportableSegmentsDetail</Role>
      <ShortName>Segment Reporting - Summary Information for Reportable Segments (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>2425402 - Disclosure - Concentration of Credit Risk - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/ConcentrationOfCreditRiskAdditionalInformationDetail</Role>
      <ShortName>Concentration of Credit Risk - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>2425403 - Disclosure - Concentration of Credit Risk - Schedule of Annualized Base Rent from Tenants at Consolidated Properties (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/ConcentrationOfCreditRiskScheduleOfAnnualizedBaseRentFromTenantsAtConsolidatedPropertiesDetail</Role>
      <ShortName>Concentration of Credit Risk - Schedule of Annualized Base Rent from Tenants at Consolidated Properties (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="gahr-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>2426401 - Disclosure - Per Share Data (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.griffincapital.com/role/PerShareDataDetail</Role>
      <ShortName>Per Share Data (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.griffincapital.com/role/PerShareData</ParentRole>
      <Position>83</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>gahr-20200331.xml</File>
    <File>gahr-20200331.xsd</File>
    <File>gahr-20200331_cal.xml</File>
    <File>gahr-20200331_def.xml</File>
    <File>gahr-20200331_lab.xml</File>
    <File>gahr-20200331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/stpr/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
