<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>347</ContextCount>
  <ElementCount>362</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>82</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>12</UnitCount>
  <MyReports>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementsofComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - Consolidated Statement of Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementofEquity</Role>
      <ShortName>Consolidated Statement of Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementsofCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - Consolidated Balance Sheets - LP</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedBalanceSheetsLP</Role>
      <ShortName>Consolidated Balance Sheets - LP</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Statement - Consolidated Balance Sheets - LP (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedBalanceSheetsLPParenthetical</Role>
      <ShortName>Consolidated Balance Sheets - LP (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Statement - Consolidated Statements of Comprehensive Income - LP</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementsofComprehensiveIncomeLP</Role>
      <ShortName>Consolidated Statements of Comprehensive Income - LP</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Statement - Consolidated Statement of Partners' Capital - LP</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementofPartnersCapitalLP</Role>
      <ShortName>Consolidated Statement of Partners' Capital - LP</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Statement - Consolidated Statements of Cash Flows - LP</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ConsolidatedStatementsofCashFlowsLP</Role>
      <ShortName>Consolidated Statements of Cash Flows - LP</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - REAL ESTATE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/REALESTATE</Role>
      <ShortName>REAL ESTATE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASES</Role>
      <ShortName>ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTS</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - DERIVATIVE AND HEDGING ACTIVITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIES</Role>
      <ShortName>DERIVATIVE AND HEDGING ACTIVITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - OTHER ASSETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERASSETS</Role>
      <ShortName>OTHER ASSETS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - OTHER LIABILITIES AND DEFERRED CREDITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERLIABILITIESANDDEFERREDCREDITS</Role>
      <ShortName>OTHER LIABILITIES AND DEFERRED CREDITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>9952168 - Disclosure - DEBT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DEBT</Role>
      <ShortName>DEBT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>9952169 - Disclosure - PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/PARTNERSCAPITALOFAMERICANASSETSTRUSTLP</Role>
      <ShortName>PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P.</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9952170 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC.</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINC</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC.</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9952171 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/INCOMETAXES</Role>
      <ShortName>INCOME TAXES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9952172 - Disclosure - COMMITMENTS AND CONTINGENCIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMMITMENTSANDCONTINGENCIES</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9952173 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASES</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9952174 - Disclosure - COMPONENTS OF RENTAL INCOME AND EXPENSE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSE</Role>
      <ShortName>COMPONENTS OF RENTAL INCOME AND EXPENSE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9952175 - Disclosure - OTHER INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERINCOME</Role>
      <ShortName>OTHER INCOME</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9952176 - Disclosure - RELATED PARTY TRANSACTIONS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/RELATEDPARTYTRANSACTIONS</Role>
      <ShortName>RELATED PARTY TRANSACTIONS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9952177 - Disclosure - SEGMENT REPORTING</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTING</Role>
      <ShortName>SEGMENT REPORTING</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPolicies</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESTables</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - REAL ESTATE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/REALESTATETables</Role>
      <ShortName>REAL ESTATE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/REALESTATE</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESTables</Role>
      <ShortName>ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASES</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSTables</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTS</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - DERIVATIVE AND HEDGING ACTIVITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIESTables</Role>
      <ShortName>DERIVATIVE AND HEDGING ACTIVITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIES</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - OTHER ASSETS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERASSETSTables</Role>
      <ShortName>OTHER ASSETS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERASSETS</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - OTHER LIABILITIES AND DEFERRED CREDITS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERLIABILITIESANDDEFERREDCREDITSTables</Role>
      <ShortName>OTHER LIABILITIES AND DEFERRED CREDITS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERLIABILITIESANDDEFERREDCREDITS</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - DEBT (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DEBTTables</Role>
      <ShortName>DEBT (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/DEBT</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC. (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCTables</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC. (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINC</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/LEASES</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - COMPONENTS OF RENTAL INCOME AND EXPENSE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSETables</Role>
      <ShortName>COMPONENTS OF RENTAL INCOME AND EXPENSE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSE</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - OTHER INCOME (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERINCOMETables</Role>
      <ShortName>OTHER INCOME (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERINCOME</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - SEGMENT REPORTING (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTINGTables</Role>
      <ShortName>SEGMENT REPORTING (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/SEGMENTREPORTING</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Supplement Disclosures Related to Consolidated Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESSummaryofSupplementDisclosuresRelatedtoConsolidatedStatementsofCashFlowsDetails</Role>
      <ShortName>SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Summary of Supplement Disclosures Related to Consolidated Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - REAL ESTATE - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/REALESTATENarrativeDetails</Role>
      <ShortName>REAL ESTATE - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - REAL ESTATE - Summary of Purchase Price Allocation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/REALESTATESummaryofPurchasePriceAllocationDetails</Role>
      <ShortName>REAL ESTATE - Summary of Purchase Price Allocation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - REAL ESTATE - Summary of Acquiree Operating Results Since Acquisition Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/REALESTATESummaryofAcquireeOperatingResultsSinceAcquisitionDateDetails</Role>
      <ShortName>REAL ESTATE - Summary of Acquiree Operating Results Since Acquisition Date (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESDetails</Role>
      <ShortName>ACQUIRED IN-PLACE LEASES AND ABOVE/BELOW MARKET LEASES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/ACQUIREDINPLACELEASESANDABOVEBELOWMARKETLEASESTables</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS - Summary of Financial Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofFinancialLiabilitiesMeasuredatFairValueonRecurringBasisDetails</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS - Summary of Financial Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSNarrativeDetails</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - FAIR VALUE OF FINANCIAL INSTRUMENTS - Summary of Carrying Amount and Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/FAIRVALUEOFFINANCIALINSTRUMENTSSummaryofCarryingAmountandFairValueofFinancialInstrumentsDetails</Role>
      <ShortName>FAIR VALUE OF FINANCIAL INSTRUMENTS - Summary of Carrying Amount and Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - DERIVATIVE AND HEDGING ACTIVITIES - Summary of Interest Rate Swap Terms (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIESSummaryofInterestRateSwapTermsDetails</Role>
      <ShortName>DERIVATIVE AND HEDGING ACTIVITIES - Summary of Interest Rate Swap Terms (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - DERIVATIVE AND HEDGING ACTIVITIES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DERIVATIVEANDHEDGINGACTIVITIESNarrativeDetails</Role>
      <ShortName>DERIVATIVE AND HEDGING ACTIVITIES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - OTHER ASSETS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERASSETSDetails</Role>
      <ShortName>OTHER ASSETS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERASSETSTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - OTHER LIABILITIES AND DEFERRED CREDITS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERLIABILITIESANDDEFERREDCREDITSDetails</Role>
      <ShortName>OTHER LIABILITIES AND DEFERRED CREDITS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERLIABILITIESANDDEFERREDCREDITSTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - DEBT - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/DEBTNarrativeDetails</Role>
      <ShortName>DEBT - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - DEBT - Summary of Total Secured Notes Payable Outstanding (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.americanassets.com/role/DEBTSummaryofTotalSecuredNotesPayableOutstandingDetails</Role>
      <ShortName>DEBT - Summary of Total Secured Notes Payable Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.americanassets.com/role/DEBTSummaryofTotalUnsecuredNotesPayableOutstandingDetails</Role>
      <ShortName>DEBT - Summary of Total Unsecured Notes Payable Outstanding (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P. (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/PARTNERSCAPITALOFAMERICANASSETSTRUSTLPDetails</Role>
      <ShortName>PARTNERS' CAPITAL OF AMERICAN ASSETS TRUST, L.P. (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/PARTNERSCAPITALOFAMERICANASSETSTRUSTLP</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC. - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCNarrativeDetails</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC. - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Dividends Declared and Paid on Shares of Common Stock and Noncontrolling Common Units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCSummaryofDividendsDeclaredandPaidonSharesofCommonStockandNoncontrollingCommonUnitsDetails</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Dividends Declared and Paid on Shares of Common Stock and Noncontrolling Common Units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Activity of Restricted Stock Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCSummaryofActivityofRestrictedStockAwardsDetails</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Activity of Restricted Stock Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Computation of Basic and Diluted EPS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/EQUITYOFAMERICANASSETSTRUSTINCSummaryofComputationofBasicandDilutedEPSDetails</Role>
      <ShortName>EQUITY OF AMERICAN ASSETS TRUST, INC. - Summary of Computation of Basic and Diluted EPS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - INCOME TAXES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/INCOMETAXESDetails</Role>
      <ShortName>INCOME TAXES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/INCOMETAXES</ParentRole>
      <Position>65</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - COMMITMENTS AND CONTINGENCIES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMMITMENTSANDCONTINGENCIESDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/COMMITMENTSANDCONTINGENCIES</ParentRole>
      <Position>66</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - LEASES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESNarrativeDetails</Role>
      <ShortName>LEASES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - LEASES - Summary of Minimum Future Rentals from Noncancelable Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESSummaryofMinimumFutureRentalsfromNoncancelableOperatingLeasesDetails</Role>
      <ShortName>LEASES - Summary of Minimum Future Rentals from Noncancelable Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9955550 - Disclosure - LEASES - Summary of Current Annual Payment Under Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESSummaryofCurrentAnnualPaymentUnderOperatingLeasesDetails</Role>
      <ShortName>LEASES - Summary of Current Annual Payment Under Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9955551 - Disclosure - LEASES - Lease Costs Under Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESLeaseCostsUnderOperatingLeasesDetails</Role>
      <ShortName>LEASES - Lease Costs Under Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9955552 - Disclosure - LEASES - Supplemental Cash Flow Information of Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/LEASESSupplementalCashFlowInformationofLeasesDetails</Role>
      <ShortName>LEASES - Supplemental Cash Flow Information of Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9955553 - Disclosure - COMPONENTS OF RENTAL INCOME AND EXPENSE - Summary of Principal Components of Rental Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSESummaryofPrincipalComponentsofRentalIncomeDetails</Role>
      <ShortName>COMPONENTS OF RENTAL INCOME AND EXPENSE - Summary of Principal Components of Rental Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9955554 - Disclosure - COMPONENTS OF RENTAL INCOME AND EXPENSE - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSENarrativeDetails</Role>
      <ShortName>COMPONENTS OF RENTAL INCOME AND EXPENSE - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9955555 - Disclosure - COMPONENTS OF RENTAL INCOME AND EXPENSE - Summary of Principal Components of Rental Expenses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/COMPONENTSOFRENTALINCOMEANDEXPENSESummaryofPrincipalComponentsofRentalExpensesDetails</Role>
      <ShortName>COMPONENTS OF RENTAL INCOME AND EXPENSE - Summary of Principal Components of Rental Expenses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9955556 - Disclosure - OTHER INCOME (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/OTHERINCOMEDetails</Role>
      <ShortName>OTHER INCOME (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/OTHERINCOMETables</ParentRole>
      <Position>75</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9955557 - Disclosure - RELATED PARTY TRANSACTIONS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/RELATEDPARTYTRANSACTIONSDetails</Role>
      <ShortName>RELATED PARTY TRANSACTIONS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.americanassets.com/role/RELATEDPARTYTRANSACTIONS</ParentRole>
      <Position>76</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9955558 - Disclosure - SEGMENT REPORTING - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTINGNarrativeDetails</Role>
      <ShortName>SEGMENT REPORTING - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9955559 - Disclosure - SEGMENT REPORTING - Summary of Segments Operating Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofSegmentsOperatingActivityDetails</Role>
      <ShortName>SEGMENT REPORTING - Summary of Segments Operating Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9955560 - Disclosure - SEGMENT REPORTING - Summary of Reconciliation of Segment Profit to Net Income Attributable to Stockholders (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofReconciliationofSegmentProfittoNetIncomeAttributabletoStockholdersDetails</Role>
      <ShortName>SEGMENT REPORTING - Summary of Reconciliation of Segment Profit to Net Income Attributable to Stockholders (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="aat-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9955561 - Disclosure - SEGMENT REPORTING - Summary of Net Real Estate and Secured Note Payable Balances by Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.americanassets.com/role/SEGMENTREPORTINGSummaryofNetRealEstateandSecuredNotePayableBalancesbySegmentsDetails</Role>
      <ShortName>SEGMENT REPORTING - Summary of Net Real Estate and Secured Note Payable Balances by Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" isDefinitelyFs="true" isUsgaap="true" original="aat-20250930.htm">aat-20250930.htm</File>
    <File>aat-20250930.xsd</File>
    <File>aat-20250930_cal.xml</File>
    <File>aat-20250930_def.xml</File>
    <File>aat-20250930_lab.xml</File>
    <File>aat-20250930_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>aat-20250930_g1.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="1338">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="42">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
