<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.24.2.u1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>1519</ContextCount>
  <ElementCount>466</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>147</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>8</UnitCount>
  <MyReports>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0000001 - Document - COVER PAGE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/COVERPAGE</Role>
      <ShortName>COVER PAGE</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>0000002 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETS</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>0000003 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDBALANCESHEETSParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>0000004 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFINCOME</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>0000005 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCOMPREHENSIVEINCOME</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>0000006 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSHAREHOLDERSEQUITY</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>0000007 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFCASHFLOWS</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>0000008 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/ORGANIZATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIES</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>0000009 - Disclosure - INVESTMENT SECURITIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIES</Role>
      <ShortName>INVESTMENT SECURITIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>0000010 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSES</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>0000011 - Disclosure - GOODWILL</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/GOODWILL</Role>
      <ShortName>GOODWILL</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>0000012 - Disclosure - LEASES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASES</Role>
      <ShortName>LEASES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>0000013 - Disclosure - DEPOSITS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DEPOSITS</Role>
      <ShortName>DEPOSITS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>0000014 - Disclosure - BORROWINGS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/BORROWINGS</Role>
      <ShortName>BORROWINGS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>0000015 - Disclosure - COMMITMENTS AND CONTINGENCIES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/COMMITMENTSANDCONTINGENCIES</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>0000016 - Disclosure - SHAREHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITY</Role>
      <ShortName>SHAREHOLDERS' EQUITY</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>0000017 - Disclosure - EARNINGS PER COMMON SHARE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/EARNINGSPERCOMMONSHARE</Role>
      <ShortName>EARNINGS PER COMMON SHARE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>0000018 - Disclosure - INCOME TAXES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INCOMETAXES</Role>
      <ShortName>INCOME TAXES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>0000019 - Disclosure - FAIR VALUE</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUE</Role>
      <ShortName>FAIR VALUE</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>0000020 - Disclosure - DERIVATIVES</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DERIVATIVES</Role>
      <ShortName>DERIVATIVES</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>0000021 - Disclosure - SEGMENT REPORTING</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SEGMENTREPORTING</Role>
      <ShortName>SEGMENT REPORTING</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>0000022 - Disclosure - LOW-INCOME HOUSING TAX CREDIT INVESTMENT</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOWINCOMEHOUSINGTAXCREDITINVESTMENT</Role>
      <ShortName>LOW-INCOME HOUSING TAX CREDIT INVESTMENT</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>0000023 - Disclosure - REGULATORY CAPITAL MATTERS</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/REGULATORYCAPITALMATTERS</Role>
      <ShortName>REGULATORY CAPITAL MATTERS</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>9954471 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/ORGANIZATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESPolicies</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>9954472 - Disclosure - INVESTMENT SECURITIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIESTables</Role>
      <ShortName>INVESTMENT SECURITIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/INVESTMENTSECURITIES</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>9954473 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESTables</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSES</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>9954474 - Disclosure - LEASES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASESTables</Role>
      <ShortName>LEASES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/LEASES</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>9954475 - Disclosure - DEPOSITS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DEPOSITSTables</Role>
      <ShortName>DEPOSITS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/DEPOSITS</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>9954476 - Disclosure - BORROWINGS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/BORROWINGSTables</Role>
      <ShortName>BORROWINGS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/BORROWINGS</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>9954477 - Disclosure - COMMITMENTS AND CONTINGENCIES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/COMMITMENTSANDCONTINGENCIESTables</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/COMMITMENTSANDCONTINGENCIES</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>9954478 - Disclosure - SHAREHOLDERS' EQUITY (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYTables</Role>
      <ShortName>SHAREHOLDERS' EQUITY (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/SHAREHOLDERSEQUITY</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>9954479 - Disclosure - EARNINGS PER COMMON SHARE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/EARNINGSPERCOMMONSHARETables</Role>
      <ShortName>EARNINGS PER COMMON SHARE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/EARNINGSPERCOMMONSHARE</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>9954480 - Disclosure - FAIR VALUE (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUETables</Role>
      <ShortName>FAIR VALUE (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/FAIRVALUE</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>9954481 - Disclosure - DERIVATIVES (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DERIVATIVESTables</Role>
      <ShortName>DERIVATIVES (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/DERIVATIVES</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>9954482 - Disclosure - SEGMENT REPORTING (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SEGMENTREPORTINGTables</Role>
      <ShortName>SEGMENT REPORTING (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/SEGMENTREPORTING</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>9954483 - Disclosure - REGULATORY CAPITAL MATTERS (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/REGULATORYCAPITALMATTERSTables</Role>
      <ShortName>REGULATORY CAPITAL MATTERS (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://myfw.com/role/REGULATORYCAPITALMATTERS</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>9954484 - Disclosure - ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Credit Risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/ORGANIZATIONANDSUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESConcentrationofCreditRiskDetails</Role>
      <ShortName>ORGANIZATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Concentration of Credit Risk (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>9954485 - Disclosure - INVESTMENT SECURITIES - Amortized cost and fair value of securities held-to-maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIESAmortizedcostandfairvalueofsecuritiesheldtomaturityDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Amortized cost and fair value of securities held-to-maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>9954486 - Disclosure - INVESTMENT SECURITIES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIESNarrativeDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>9954487 - Disclosure - INVESTMENT SECURITIES - Amortized cost and estimated fair value of available-for-sale securities excluding SBIC (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIESAmortizedcostandestimatedfairvalueofavailableforsalesecuritiesexcludingSBICDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Amortized cost and estimated fair value of available-for-sale securities excluding SBIC (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>9954488 - Disclosure - INVESTMENT SECURITIES - Allowance for credit losses to HTM securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INVESTMENTSECURITIESAllowanceforcreditlossestoHTMsecuritiesDetails</Role>
      <ShortName>INVESTMENT SECURITIES - Allowance for credit losses to HTM securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>9954489 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Summary of loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESSummaryofloansDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Summary of loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>9954490 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESNarrativeDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>9954491 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Aging analysis of recorded investments by class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESAginganalysisofrecordedinvestmentsbyclassDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Aging analysis of recorded investments by class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>9954492 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Loan modification (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESLoanmodificationDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Loan modification (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>9954493 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Recorded investment in non-accrual loans by class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESRecordedinvestmentinnonaccrualloansbyclassDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Recorded investment in non-accrual loans by class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>9954494 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Summary of nonaccrual loans with collateral (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESSummaryofnonaccrualloanswithcollateralDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Summary of nonaccrual loans with collateral (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>9954495 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Allowance for loan losses by portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESAllowanceforloanlossesbyportfolioDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Allowance for loan losses by portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>9954496 - Disclosure - LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Recorded investment in company's loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOANSANDTHEALLOWANCEFORCREDITLOSSESRecordedinvestmentincompanysloansDetails</Role>
      <ShortName>LOANS AND THE ALLOWANCE FOR CREDIT LOSSES - Recorded investment in company's loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>9954497 - Disclosure - GOODWILL - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/GOODWILLNarrativeDetails</Role>
      <ShortName>GOODWILL - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>9954498 - Disclosure - LEASES - Leases balance sheet location (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASESLeasesbalancesheetlocationDetails</Role>
      <ShortName>LEASES - Leases balance sheet location (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>9954499 - Disclosure - LEASES - Leases costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASESLeasescostsDetails</Role>
      <ShortName>LEASES - Leases costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>9954500 - Disclosure - LEASES - Lease maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASESLeasematurityDetails</Role>
      <ShortName>LEASES - Lease maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>9954501 - Disclosure - LEASES - Expected amortization expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LEASESExpectedamortizationexpenseDetails</Role>
      <ShortName>LEASES - Expected amortization expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>9954502 - Disclosure - DEPOSITS - Schedule of interest-bearing deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DEPOSITSScheduleofinterestbearingdepositsDetails</Role>
      <ShortName>DEPOSITS - Schedule of interest-bearing deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>9954503 - Disclosure - DEPOSITS - Schedule of time deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DEPOSITSScheduleoftimedepositsDetails</Role>
      <ShortName>DEPOSITS - Schedule of time deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>9954504 - Disclosure - BORROWINGS - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/BORROWINGSNarrativeDetails</Role>
      <ShortName>BORROWINGS - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>9954505 - Disclosure - BORROWINGS - Schedule of borrowings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/BORROWINGSScheduleofborrowingsDetails</Role>
      <ShortName>BORROWINGS - Schedule of borrowings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>9954506 - Disclosure - BORROWINGS - Schedule of subordinated debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/BORROWINGSScheduleofsubordinateddebtDetails</Role>
      <ShortName>BORROWINGS - Schedule of subordinated debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>9954507 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of financial instruments with credit risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/COMMITMENTSANDCONTINGENCIESScheduleoffinancialinstrumentswithcreditriskDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of financial instruments with credit risk (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>9954508 - Disclosure - COMMITMENTS AND CONTINGENCIES - Schedule of unfunded loan commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/COMMITMENTSANDCONTINGENCIESScheduleofunfundedloancommitmentsDetails</Role>
      <ShortName>COMMITMENTS AND CONTINGENCIES - Schedule of unfunded loan commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>9954509 - Disclosure - SHAREHOLDERS' EQUITY - Common stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYCommonstockDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Common stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>9954510 - Disclosure - SHAREHOLDERS' EQUITY - Stock based compensation plans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYStockbasedcompensationplansDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Stock based compensation plans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>9954511 - Disclosure - SHAREHOLDERS' EQUITY - Stock options activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYStockoptionsactivityDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Stock options activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>9954512 - Disclosure - SHAREHOLDERS' EQUITY - Share awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYShareawardsDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Share awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>9954513 - Disclosure - SHAREHOLDERS' EQUITY - Time vesting units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYTimevestingunitsDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Time vesting units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>9954514 - Disclosure - SHAREHOLDERS' EQUITY - Financial performance units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SHAREHOLDERSEQUITYFinancialperformanceunitsDetails</Role>
      <ShortName>SHAREHOLDERS' EQUITY - Financial performance units (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>9954515 - Disclosure - EARNINGS PER COMMON SHARE - Computation of earnings per share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/EARNINGSPERCOMMONSHAREComputationofearningspershareDetails</Role>
      <ShortName>EARNINGS PER COMMON SHARE - Computation of earnings per share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>9954516 - Disclosure - EARNINGS PER COMMON SHARE - Schedule of potentially dilutive Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/EARNINGSPERCOMMONSHAREScheduleofpotentiallydilutiveSecuritiesDetails</Role>
      <ShortName>EARNINGS PER COMMON SHARE - Schedule of potentially dilutive Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>9954517 - Disclosure - INCOME TAXES (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/INCOMETAXESDetails</Role>
      <ShortName>INCOME TAXES (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://myfw.com/role/INCOMETAXES</ParentRole>
      <Position>70</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>9954518 - Disclosure - FAIR VALUE - Summary of assets measured at fair value on recurring basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofassetsmeasuredatfairvalueonrecurringbasisDetails</Role>
      <ShortName>FAIR VALUE - Summary of assets measured at fair value on recurring basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>9954519 - Disclosure - FAIR VALUE - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUENarrativeDetails</Role>
      <ShortName>FAIR VALUE - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>9954520 - Disclosure - FAIR VALUE - Summary of information about the fair value carrying amount and unpaid principal outstanding of loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofinformationaboutthefairvaluecarryingamountandunpaidprincipaloutstandingofloansDetails</Role>
      <ShortName>FAIR VALUE - Summary of information about the fair value carrying amount and unpaid principal outstanding of loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>9954521 - Disclosure - FAIR VALUE - Summary of changes in fair value of loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofchangesinfairvalueofloansDetails</Role>
      <ShortName>FAIR VALUE - Summary of changes in fair value of loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>9954522 - Disclosure - FAIR VALUE - Rollforward of changes in fair value of loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUERollforwardofchangesinfairvalueofloansDetails</Role>
      <ShortName>FAIR VALUE - Rollforward of changes in fair value of loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>9954523 - Disclosure - FAIR VALUE - Summary of assets measured at fair value on nonrecurring basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofassetsmeasuredatfairvalueonnonrecurringbasisDetails</Role>
      <ShortName>FAIR VALUE - Summary of assets measured at fair value on nonrecurring basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>9954524 - Disclosure - FAIR VALUE - Summary of assets measured at fair value on recurring basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofassetsmeasuredatfairvalueonrecurringbasisDetails_1</Role>
      <ShortName>FAIR VALUE - Summary of assets measured at fair value on recurring basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>9954525 - Disclosure - FAIR VALUE - Summary of assets measured at level 3 fair value on recurring basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofassetsmeasuredatlevel3fairvalueonrecurringbasisDetails</Role>
      <ShortName>FAIR VALUE - Summary of assets measured at level 3 fair value on recurring basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>9954526 - Disclosure - FAIR VALUE - Summary of assets and liabilities measured at fair value on a recurring or nonrecurring, the significant unobservable inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofassetsandliabilitiesmeasuredatfairvalueonarecurringornonrecurringthesignificantunobservableinputsDetails</Role>
      <ShortName>FAIR VALUE - Summary of assets and liabilities measured at fair value on a recurring or nonrecurring, the significant unobservable inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>9954527 - Disclosure - FAIR VALUE - Summary of carrying amounts and estimated fair values for financial instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/FAIRVALUESummaryofcarryingamountsandestimatedfairvaluesforfinancialinstrumentsDetails</Role>
      <ShortName>FAIR VALUE - Summary of carrying amounts and estimated fair values for financial instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>9954528 - Disclosure - DERIVATIVES - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DERIVATIVESNarrativeDetails</Role>
      <ShortName>DERIVATIVES - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>9954529 - Disclosure - DERIVATIVES - Schedule of Derivatives by Balance Sheet Location (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DERIVATIVESScheduleofDerivativesbyBalanceSheetLocationDetails</Role>
      <ShortName>DERIVATIVES - Schedule of Derivatives by Balance Sheet Location (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>9954530 - Disclosure - DERIVATIVES - Derivative Reclassified into Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/DERIVATIVESDerivativeReclassifiedintoIncomeDetails</Role>
      <ShortName>DERIVATIVES - Derivative Reclassified into Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>9954531 - Disclosure - SEGMENT REPORTING (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/SEGMENTREPORTINGDetails</Role>
      <ShortName>SEGMENT REPORTING (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://myfw.com/role/SEGMENTREPORTINGTables</ParentRole>
      <Position>84</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>9954532 - Disclosure - LOW-INCOME HOUSING TAX CREDIT INVESTMENT (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/LOWINCOMEHOUSINGTAXCREDITINVESTMENTDetails</Role>
      <ShortName>LOW-INCOME HOUSING TAX CREDIT INVESTMENT (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://myfw.com/role/LOWINCOMEHOUSINGTAXCREDITINVESTMENT</ParentRole>
      <Position>85</Position>
    </Report>
    <Report instance="myfw-20240630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>9954533 - Disclosure - REGULATORY CAPITAL MATTERS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://myfw.com/role/REGULATORYCAPITALMATTERSDetails</Role>
      <ShortName>REGULATORY CAPITAL MATTERS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://myfw.com/role/REGULATORYCAPITALMATTERSTables</ParentRole>
      <Position>86</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="myfw-20240630.htm">myfw-20240630.htm</File>
    <File>myfw-20240630.xsd</File>
    <File>myfw-20240630_cal.xml</File>
    <File>myfw-20240630_def.xml</File>
    <File>myfw-20240630_lab.xml</File>
    <File>myfw-20240630_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="2530">http://fasb.org/us-gaap/2023</BaseTaxonomy>
    <BaseTaxonomy items="30">http://xbrl.sec.gov/dei/2023</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
