<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>752</ContextCount>
  <ElementCount>406</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>78</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>9952151 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFFINANCIALCONDITIONUNAUDITED</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>9952152 - Statement - CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (UNAUDITED)?? (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFFINANCIALCONDITIONUNAUDITEDParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF FINANCIAL CONDITION (UNAUDITED)?? (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>9952153 - Statement - CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFOPERATIONSUNAUDITED</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF OPERATIONS (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>9952154 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUNAUDITED</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>9952155 - Statement - CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)?? (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOMEUNAUDITEDParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (UNAUDITED)?? (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>9952156 - Statement - CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITYUNAUDITED</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>9952157 - Statement - CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED)?? (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITYUNAUDITEDParenthetical</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY (UNAUDITED)?? (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>9952158 - Statement - CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CONSOLIDATEDSTATEMENTSOFCASHFLOWSUNAUDITED</Role>
      <ShortName>CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>9952159 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>9952160 - Disclosure - Business Combination</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/BusinessCombination</Role>
      <ShortName>Business Combination</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>9952161 - Disclosure - Dividends and Share Repurchases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DividendsandShareRepurchases</Role>
      <ShortName>Dividends and Share Repurchases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>9952162 - Disclosure - Loans Receivable</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivable</Role>
      <ShortName>Loans Receivable</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>9952163 - Disclosure - Allowance for Losses on Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoans</Role>
      <ShortName>Allowance for Losses on Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>9952164 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>9952165 - Disclosure - Derivatives and Hedging Activities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivities</Role>
      <ShortName>Derivatives and Hedging Activities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>9952166 - Disclosure - Revenue from Contracts with Customers</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/RevenuefromContractswithCustomers</Role>
      <ShortName>Revenue from Contracts with Customers</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>9952167 - Disclosure - Commitment and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CommitmentandContingencies</Role>
      <ShortName>Commitment and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.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>20</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>9955511 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>9955512 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPolicies</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>9955513 - Disclosure - Business Combination (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/BusinessCombinationTables</Role>
      <ShortName>Business Combination (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/BusinessCombination</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9955514 - Disclosure - Loans Receivable (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableTables</Role>
      <ShortName>Loans Receivable (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/LoansReceivable</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9955515 - Disclosure - Allowance for Losses on Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoansTables</Role>
      <ShortName>Allowance for Losses on Loans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/AllowanceforLossesonLoans</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9955516 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/FairValueMeasurements</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9955517 - Disclosure - Derivatives and Hedging Activities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesTables</Role>
      <ShortName>Derivatives and Hedging Activities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/DerivativesandHedgingActivities</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9955518 - Disclosure - Commitment and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CommitmentandContingenciesTables</Role>
      <ShortName>Commitment and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/CommitmentandContingencies</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9955519 - Disclosure - Summary of Significant Accounting Policies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPoliciesNarrativeDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9955520 - Disclosure - Summary of Significant Accounting Policies - Schedule of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPoliciesScheduleofIntangibleAssetsDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9955521 - Disclosure - Summary of Significant Accounting Policies - Schedule of Future Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/SummaryofSignificantAccountingPoliciesScheduleofFutureAmortizationExpenseDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Schedule of Future Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9955522 - Disclosure - Business Combination - Schedule of Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/BusinessCombinationScheduleofAssetsAcquiredandLiabilitiesAssumedDetails</Role>
      <ShortName>Business Combination - Schedule of Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9955523 - Disclosure - Business Combination - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/BusinessCombinationNarrativeDetails</Role>
      <ShortName>Business Combination - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9955524 - Disclosure - Business Combination - Schedule of Pro Forma Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/BusinessCombinationScheduleofProFormaInformationDetails</Role>
      <ShortName>Business Combination - Schedule of Pro Forma Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9955525 - Disclosure - Dividends and Share Repurchases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DividendsandShareRepurchasesDetails</Role>
      <ShortName>Dividends and Share Repurchases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/DividendsandShareRepurchases</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9955526 - Disclosure - Loans Receivable - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableNarrativeDetails</Role>
      <ShortName>Loans Receivable - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9955527 - Disclosure - Loans Receivable - Schedule of Loans Receivable (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableScheduleofLoansReceivableDetails</Role>
      <ShortName>Loans Receivable - Schedule of Loans Receivable (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9955528 - Disclosure - Loans Receivable - Non-accrual Loans and Loans 90 Days or More Past Due and Accruing (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableNonaccrualLoansandLoans90DaysorMorePastDueandAccruingDetails</Role>
      <ShortName>Loans Receivable - Non-accrual Loans and Loans 90 Days or More Past Due and Accruing (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9955529 - Disclosure - Loans Receivable - Loan Delinquencies by Loan Portfolio and Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableLoanDelinquenciesbyLoanPortfolioandClassDetails</Role>
      <ShortName>Loans Receivable - Loan Delinquencies by Loan Portfolio and Class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9955530 - Disclosure - Loans Receivable - Schedule of Collateral-Dependent Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableScheduleofCollateralDependentLoansDetails</Role>
      <ShortName>Loans Receivable - Schedule of Collateral-Dependent Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9955531 - Disclosure - Loans Receivable - Schedule of Loan Modifications (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableScheduleofLoanModificationsDetails</Role>
      <ShortName>Loans Receivable - Schedule of Loan Modifications (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9955532 - Disclosure - Loans Receivable - Schedule of Loan Performance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableScheduleofLoanPerformanceDetails</Role>
      <ShortName>Loans Receivable - Schedule of Loan Performance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9955533 - Disclosure - Loans Receivable - Loans Based on Credit Quality Indicators (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/LoansReceivableLoansBasedonCreditQualityIndicatorsDetails</Role>
      <ShortName>Loans Receivable - Loans Based on Credit Quality Indicators (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9955534 - Disclosure - Allowance for Losses on Loans - Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoansAllowanceforLoanLossesDetails</Role>
      <ShortName>Allowance for Losses on Loans - Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9955535 - Disclosure - Allowance for Losses on Loans - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoansNarrativeDetails</Role>
      <ShortName>Allowance for Losses on Loans - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9955536 - Disclosure - Allowance for Losses on Loans - Internally Assigned Grade (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoansInternallyAssignedGradeDetails</Role>
      <ShortName>Allowance for Losses on Loans - Internally Assigned Grade (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9955537 - Disclosure - Allowance for Losses on Loans - Credit Risk Profile Based on Payment Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/AllowanceforLossesonLoansCreditRiskProfileBasedonPaymentActivityDetails</Role>
      <ShortName>Allowance for Losses on Loans - Credit Risk Profile Based on Payment Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9955538 - Disclosure - Fair Value Measurements - Fair Value Measured on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsFairValueMeasuredonRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Fair Value Measured on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9955539 - Disclosure - Fair Value Measurements - Fair Value Measured on Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsFairValueMeasuredonNonrecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Fair Value Measured on Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9955540 - Disclosure - Fair Value Measurements - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsNarrativeDetails</Role>
      <ShortName>Fair Value Measurements - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9955541 - Disclosure - Fair Value Measurements - Fair Value by Balance Sheet Grouping (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsFairValuebyBalanceSheetGroupingDetails</Role>
      <ShortName>Fair Value Measurements - Fair Value by Balance Sheet Grouping (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9955542 - Disclosure - Fair Value Measurements - Investments by Contractual Maturity Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsInvestmentsbyContractualMaturityDateDetails</Role>
      <ShortName>Fair Value Measurements - Investments by Contractual Maturity Date (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9955543 - Disclosure - Fair Value Measurements - Securities in Unrealized Loss Positions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/FairValueMeasurementsSecuritiesinUnrealizedLossPositionsDetails</Role>
      <ShortName>Fair Value Measurements - Securities in Unrealized Loss Positions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9955544 - Disclosure - Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesSummaryofFairValueNotionalAmountandBalanceSheetClassificationDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Summary of Fair Value, Notional Amount and Balance Sheet Classification (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9955545 - Disclosure - Derivatives and Hedging Activities - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesImpactofFairValueHedgeAccountingontheCarryingValueoftheHedgedItemsDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Impact of Fair Value Hedge Accounting on the Carrying Value of the Hedged Items (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9955546 - Disclosure - Derivatives and Hedging Activities - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesNarrativeDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9955547 - Disclosure - Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesImpactofDerivativeInstrumentsonAOCIDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Impact of Derivative Instruments on AOCI (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9955548 - Disclosure - Derivatives and Hedging Activities - Gains/(Losses) on Derivative Instruments in Fair Value and Cash Flow Accounting Hedging Relationships (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesGainsLossesonDerivativeInstrumentsinFairValueandCashFlowAccountingHedgingRelationshipsDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Gains/(Losses) on Derivative Instruments in Fair Value and Cash Flow Accounting Hedging Relationships (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9955549 - Disclosure - Derivatives and Hedging Activities - Impact of Client Swap Program that are Not Designated in Accounting Hedges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/DerivativesandHedgingActivitiesImpactofClientSwapProgramthatareNotDesignatedinAccountingHedgesDetails</Role>
      <ShortName>Derivatives and Hedging Activities - Impact of Client Swap Program that are Not Designated in Accounting Hedges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9955550 - Disclosure - Revenue from Contracts with Customers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/RevenuefromContractswithCustomersDetails</Role>
      <ShortName>Revenue from Contracts with Customers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/RevenuefromContractswithCustomers</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="wfsl-20241231.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9955551 - Disclosure - Commitment and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.washingtonfederal.com/role/CommitmentandContingenciesDetails</Role>
      <ShortName>Commitment and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.washingtonfederal.com/role/CommitmentandContingenciesTables</ParentRole>
      <Position>61</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="wfsl-20241231.htm">wfsl-20241231.htm</File>
    <File>wfsl-20241231.xsd</File>
    <File>wfsl-20241231_cal.xml</File>
    <File>wfsl-20241231_def.xml</File>
    <File>wfsl-20241231_lab.xml</File>
    <File>wfsl-20241231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="2493">http://fasb.org/us-gaap/2024</BaseTaxonomy>
    <BaseTaxonomy items="32">http://xbrl.sec.gov/dei/2024</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2024</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
