<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>308</ContextCount>
  <ElementCount>353</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>53</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001000 - Document - Document and Entity Information Document</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DocumentAndEntityInformationDocument</Role>
      <ShortName>Document and Entity Information Document</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001000 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002500 - Statement - Balance Sheet Parenthetical (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/BalanceSheetParentheticalParentheticals</Role>
      <ShortName>Balance Sheet Parenthetical (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003000 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ConsolidatedStatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004000 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005000 - Statement - Consolidated Statements of Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ConsolidatedStatementsOfStockholdersEquity</Role>
      <ShortName>Consolidated Statements of Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1006500 - Statement - Stockholders' Equity Parenthetical (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/StockholdersEquityParentheticalParentheticals</Role>
      <ShortName>Stockholders' Equity Parenthetical (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1007000 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101100 - Disclosure - Organization and Nature of Business and Summary of Significant Accounting Policies (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/OrganizationAndNatureOfBusinessAndSummaryOfSignificantAccountingPoliciesNotes</Role>
      <ShortName>Organization and Nature of Business and Summary of Significant Accounting Policies (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2103100 - Disclosure - Earnings Per Common Share (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/EarningsPerCommonShareNotes</Role>
      <ShortName>Earnings Per Common Share (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2104100 - Disclosure - Investment Securities (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesNotes</Role>
      <ShortName>Investment Securities (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2105100 - Disclosure - Loans and Allowance for Loan Losses (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesNotes</Role>
      <ShortName>Loans and Allowance for Loan Losses (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2109100 - Disclosure - Derivatives (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/DerivativesNotes</Role>
      <ShortName>Derivatives (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2111100 - Disclosure - Deferred Income Taxes (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/DeferredIncomeTaxesNotes</Role>
      <ShortName>Deferred Income Taxes (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2112100 - Disclosure - Comprehensive Income (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/ComprehensiveIncomeNotes</Role>
      <ShortName>Comprehensive Income (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2113100 - Disclosure - Commitments and Contingencies (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/CommitmentsAndContingenciesNotes</Role>
      <ShortName>Commitments and Contingencies (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2114100 - Disclosure - Fair Value Measurements (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsNotes</Role>
      <ShortName>Fair Value Measurements (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2115100 - Disclosure - Risks and Uncertainities (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://westbankiowa.com/role/RisksAndUncertainitiesNotes</Role>
      <ShortName>Risks and Uncertainities (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2201201 - Disclosure - Basis of Presentation (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/BasisOfPresentationPolicies</Role>
      <ShortName>Basis of Presentation (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/OrganizationAndNatureOfBusinessAndSummaryOfSignificantAccountingPoliciesNotes</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2303301 - Disclosure - Earnings Per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/EarningsPerCommonShareTables</Role>
      <ShortName>Earnings Per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/EarningsPerCommonShareNotes</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesTables</Role>
      <ShortName>Investment Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/InvestmentSecuritiesNotes</ParentRole>
      <Position>21</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2305301 - Disclosure - Loans and Allowance for Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesTables</Role>
      <ShortName>Loans and Allowance for Loan Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesNotes</ParentRole>
      <Position>22</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2309301 - Disclosure - Derivatives (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DerivativesTables</Role>
      <ShortName>Derivatives (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/DerivativesNotes</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2311301 - Disclosure - Deferred Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DeferredIncomeTaxesTables</Role>
      <ShortName>Deferred Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/DeferredIncomeTaxesNotes</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2312301 - Disclosure - Comprehensive Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ComprehensiveIncomeTables</Role>
      <ShortName>Comprehensive Income (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/ComprehensiveIncomeNotes</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2313301 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/CommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/CommitmentsAndContingenciesNotes</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2314301 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/FairValueMeasurementsNotes</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2403402 - Disclosure - Earnings Per Common Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/EarningsPerCommonShareDetails</Role>
      <ShortName>Earnings Per Common Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/EarningsPerCommonShareTables</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Investment Securities Security Type - Available for Sale (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesSecurityTypeAvailableForSaleDetails</Role>
      <ShortName>Investment Securities Security Type - Available for Sale (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2404403 - Disclosure - Investment Securities Contractual Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesContractualMaturitiesDetails</Role>
      <ShortName>Investment Securities Contractual Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2404404 - Disclosure - Investment Securities Detail of Sale of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesDetailOfSaleOfSecuritiesDetails</Role>
      <ShortName>Investment Securities Detail of Sale of Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2404405 - Disclosure - Investment Securities Gross Unrealized Losses - AFS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesGrossUnrealizedLossesAfsDetails</Role>
      <ShortName>Investment Securities Gross Unrealized Losses - AFS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2404406 - Disclosure - Investment Securities Other Narratives - AFS securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/InvestmentSecuritiesOtherNarrativesAfsSecuritiesDetails</Role>
      <ShortName>Investment Securities Other Narratives - AFS securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2405402 - Disclosure - Loans and Allowance for Loan Losses Schedule of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2405403 - Disclosure - Loans and Allowance for Loan Losses Schedule of Troubled Debt Restructured Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfTroubledDebtRestructuredLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Troubled Debt Restructured Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2405404 - Disclosure - Loans and Allowance for Loan Losses Schedule of Impaired Loans With and Without an Allowance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfImpairedLoansWithAndWithoutAllowanceDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Impaired Loans With and Without an Allowance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2405405 - Disclosure - Loans and Allowance for Loan Losses Schedule of Impaired Loans With and Without an Allowance 2 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfImpairedLoansWithAndWithoutAllowance2Details</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Impaired Loans With and Without an Allowance 2 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2405406 - Disclosure - Loans and Allowance for Loan Losses Schedule of Past Due Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfPastDueLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Past Due Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2405407 - Disclosure - Loans and Allowance for Loan Losses Schedule of Loans By Credit Quality Indicator (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfLoansByCreditQualityIndicatorDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Loans By Credit Quality Indicator (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2405408 - Disclosure - Loans and Allowance for Loan Losses Schedule of Allowance for Loan Loss Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfAllowanceForLoanLossActivityDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Allowance for Loan Loss Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2405409 - Disclosure - Loans and Allowance for Loan Losses Schedule of Allowance for Loan Losses by Impairment Method (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfAllowanceForLoanLossesByImpairmentMethodDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Allowance for Loan Losses by Impairment Method (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2405410 - Disclosure - Loans and Allowance for Loan Losses Schedule of Loans by Impairment Method (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesScheduleOfLoansByImpairmentMethodDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Schedule of Loans by Impairment Method (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2405411 - Disclosure - Loans and Allowance for Loan Losses Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/LoansAndAllowanceForLoanLossesNarrativeDetails</Role>
      <ShortName>Loans and Allowance for Loan Losses Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2409402 - Disclosure - Derivatives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DerivativesDetails</Role>
      <ShortName>Derivatives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/DerivativesTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Derivatives Pre-Tax Gains (Losses) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DerivativesPreTaxGainsLossesDetails</Role>
      <ShortName>Derivatives Pre-Tax Gains (Losses) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2411402 - Disclosure - Deferred Income Taxes Schedule of Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DeferredIncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>Deferred Income Taxes Schedule of Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2411403 - Disclosure - Deferred Income Taxes Operating Loss Carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DeferredIncomeTaxesOperatingLossCarryforwardsDetails</Role>
      <ShortName>Deferred Income Taxes Operating Loss Carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2411404 - Disclosure - Deferred Income Taxes Capital loss carryforwards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/DeferredIncomeTaxesCapitalLossCarryforwardsDetails</Role>
      <ShortName>Deferred Income Taxes Capital loss carryforwards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2412402 - Disclosure - Comprehensive Income Changes in Accumulated Other Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/ComprehensiveIncomeChangesInAccumulatedOtherComprehensiveIncomeDetails</Role>
      <ShortName>Comprehensive Income Changes in Accumulated Other Comprehensive Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2413402 - Disclosure - Commitments and Contingencies (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/CommitmentsAndContingenciesDetails</Role>
      <ShortName>Commitments and Contingencies (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://westbankiowa.com/role/CommitmentsAndContingenciesTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2413403 - Disclosure - Commitments and Contingencies Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/CommitmentsAndContingenciesNarrativeDetails</Role>
      <ShortName>Commitments and Contingencies Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2414402 - Disclosure - Fair Value Measurements Recurring Basis by Level (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsRecurringBasisByLevelDetails</Role>
      <ShortName>Fair Value Measurements Recurring Basis by Level (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2414403 - Disclosure - Fair Value Measurements Nonrecurring Basis by Level (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsNonrecurringBasisByLevelDetails</Role>
      <ShortName>Fair Value Measurements Nonrecurring Basis by Level (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2414404 - Disclosure - Fair Value Measurements Carrying Amounts and Fair Values (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsCarryingAmountsAndFairValuesDetails</Role>
      <ShortName>Fair Value Measurements Carrying Amounts and Fair Values (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="wtba-20200331.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2414405 - Disclosure - Fair Value Measurements Fair Value Measurements Narratives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://westbankiowa.com/role/FairValueMeasurementsFairValueMeasurementsNarrativesDetails</Role>
      <ShortName>Fair Value Measurements Fair Value Measurements Narratives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>wtba-20200331.xml</File>
    <File>wtba-20200331.xsd</File>
    <File>wtba-20200331_cal.xml</File>
    <File>wtba-20200331_def.xml</File>
    <File>wtba-20200331_lab.xml</File>
    <File>wtba-20200331_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2019-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
