<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.6.0.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>639</ContextCount>
  <ElementCount>670</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>142</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>10</UnitCount>
  <MyReports>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>00090 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>00100 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>00105 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>00200 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedStatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>00300 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>00400 - Statement - Consolidated Statements Of Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedStatementsOfEquity</Role>
      <ShortName>Consolidated Statements Of Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>00405 - Statement - Consolidated Statements Of Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementConsolidatedStatementsOfEquityParenthetical</Role>
      <ShortName>Consolidated Statements Of Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>00500 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/StatementCondensedConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>10201 - Disclosure - Discontinued Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDiscontinuedOperations</Role>
      <ShortName>Discontinued Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>10301 - Disclosure - Investments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestments</Role>
      <ShortName>Investments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>10401 - Disclosure - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoans</Role>
      <ShortName>Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>10501 - Disclosure - Premises And Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipment</Role>
      <ShortName>Premises And Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>10601 - Disclosure - Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIntangibleAssets</Role>
      <ShortName>Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>10701 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDeposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>10801 - Disclosure - Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureBorrowedFunds</Role>
      <ShortName>Borrowed Funds</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>10901 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>11001 - Disclosure - Derivatives</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivatives</Role>
      <ShortName>Derivatives</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>11101 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>11201 - Disclosure - Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureShareholdersEquity</Role>
      <ShortName>Shareholders' Equity</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>11301 - Disclosure - Accumulated Other Comprehensive Income (Loss) Reclassifications</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureAccumulatedOtherComprehensiveIncomeLossReclassifications</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) Reclassifications</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>11401 - Disclosure - Earnings per Common Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEarningsPerCommonShare</Role>
      <ShortName>Earnings per Common Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>11501 - Disclosure - Employee Benefit and Stock Compensation Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlans</Role>
      <ShortName>Employee Benefit and Stock Compensation Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>11601 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>11701 - Disclosure - Regulatory Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureRegulatoryMatters</Role>
      <ShortName>Regulatory Matters</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>11801 - Disclosure - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurements</Role>
      <ShortName>Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>11901 - Disclosure - Segments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSegments</Role>
      <ShortName>Segments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>12001 - Disclosure - Condensed Financial Statements Of Parent Company</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompany</Role>
      <ShortName>Condensed Financial Statements Of Parent Company</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>12101 - Disclosure - Supplemental Financial Data</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSupplementalFinancialData</Role>
      <ShortName>Supplemental Financial Data</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>12201 - Disclosure - Selected Quarterly Financial Data (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSelectedQuarterlyFinancialDataUnaudited</Role>
      <ShortName>Selected Quarterly Financial Data (Unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>20102 - Disclosure - Nature Of Operations and Significant Accounting Policies (Policy)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesPolicy</Role>
      <ShortName>Nature Of Operations and Significant Accounting Policies (Policy)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>30103 - Disclosure - Nature of Operations and Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesTables</Role>
      <ShortName>Nature of Operations and Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>30203 - Disclosure - Discontinued Operations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDiscontinuedOperationsTables</Role>
      <ShortName>Discontinued Operations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureDiscontinuedOperations</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>30303 - Disclosure - Investments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsTables</Role>
      <ShortName>Investments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureInvestments</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>30403 - Disclosure - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansTables</Role>
      <ShortName>Loans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureLoans</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>30503 - Disclosure - Premises And Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipmentTables</Role>
      <ShortName>Premises And Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipment</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>30603 - Disclosure - Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIntangibleAssetsTables</Role>
      <ShortName>Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureIntangibleAssets</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>30703 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureDeposits</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>30803 - Disclosure - Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureBorrowedFundsTables</Role>
      <ShortName>Borrowed Funds (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureBorrowedFunds</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>30903 - Disclosure - Long-Term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebtTables</Role>
      <ShortName>Long-Term Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureLongTermDebt</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>31003 - Disclosure - Derivatives (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivativesTables</Role>
      <ShortName>Derivatives (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureDerivatives</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>31103 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureIncomeTaxes</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>31203 - Disclosure - Shareholders' Equity (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureShareholdersEquityTables</Role>
      <ShortName>Shareholders' Equity (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureShareholdersEquity</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>31303 - Disclosure - Accumulated Other Comprehensive Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureAccumulatedOtherComprehensiveIncomeTables</Role>
      <ShortName>Accumulated Other Comprehensive Income (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureAccumulatedOtherComprehensiveIncomeLossReclassifications</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>31403 - Disclosure - Earnings per Common Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEarningsPerCommonShareTables</Role>
      <ShortName>Earnings per Common Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureEarningsPerCommonShare</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>31503 - Disclosure - Employee Benefit and Stock Compensation Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansTables</Role>
      <ShortName>Employee Benefit and Stock Compensation Plans (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlans</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>31603 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>31703 - Disclosure - Regulatory Matters (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureRegulatoryMattersTables</Role>
      <ShortName>Regulatory Matters (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureRegulatoryMatters</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>31803 - Disclosure - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsTables</Role>
      <ShortName>Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurements</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>31903 - Disclosure - Segments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSegmentsTables</Role>
      <ShortName>Segments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureSegments</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>32003 - Disclosure - Condensed Financial Statements Of Parent Company (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompanyTables</Role>
      <ShortName>Condensed Financial Statements Of Parent Company (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompany</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>32103 - Disclosure - Supplemental Financial Data (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSupplementalFinancialDataTables</Role>
      <ShortName>Supplemental Financial Data (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureSupplementalFinancialData</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>32203 - Disclosure - Selected Quarterly Financial Data (Unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSelectedQuarterlyFinancialDataUnauditedTables</Role>
      <ShortName>Selected Quarterly Financial Data (Unaudited) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureSelectedQuarterlyFinancialDataUnaudited</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>40101 - Disclosure - Nature of Operations and Significant Accounting Policies - Organization (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesOrganizationDetails</Role>
      <ShortName>Nature of Operations and Significant Accounting Policies - Organization (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>40102 - Disclosure - Nature of Operations and Significant Accounting Policies - Cash and Cash Equivalents (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesCashAndCashEquivalentsDetails</Role>
      <ShortName>Nature of Operations and Significant Accounting Policies - Cash and Cash Equivalents (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>40103 - Disclosure - Nature Of Operations and Significant Accounting Policies - Restricted Cash to Other Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesRestrictedCashToOtherAssetsDetails</Role>
      <ShortName>Nature Of Operations and Significant Accounting Policies - Restricted Cash to Other Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>40104 - Disclosure - Nature Of Operations and Significant Accounting Policies - Repossessed Assets and OREO (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureNatureOfOperationsAndSignificantAccountingPoliciesRepossessedAssetsAndOreoDetails</Role>
      <ShortName>Nature Of Operations and Significant Accounting Policies - Repossessed Assets and OREO (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>40201 - Disclosure - Discontinued Operations - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDiscontinuedOperationsNarrativeDetails</Role>
      <ShortName>Discontinued Operations - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>40202 - Disclosure - Discontinued Operations - Schedule Of Discontinued Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDiscontinuedOperationsScheduleOfDiscontinuedOperationsDetails</Role>
      <ShortName>Discontinued Operations - Schedule Of Discontinued Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>40301 - Disclosure - Investments - Reconciliation from Amortized Cost to Fair Value of Investment Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsReconciliationFromAmortizedCostToFairValueOfInvestmentSecuritiesDetails</Role>
      <ShortName>Investments - Reconciliation from Amortized Cost to Fair Value of Investment Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>40302 - Disclosure - Investments - Transfers (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsTransfersDetails</Role>
      <ShortName>Investments - Transfers (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>40303 - Disclosure - Investments - Schedule of Proceeds and Gains (Losses) from Securities Sold or Called (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsScheduleOfProceedsAndGainsLossesFromSecuritiesSoldOrCalledDetails</Role>
      <ShortName>Investments - Schedule of Proceeds and Gains (Losses) from Securities Sold or Called (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>40304 - Disclosure - Investments - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsScheduleOfAmortizedCostAndEstimatedFairValueOfInvestmentSecuritiesByContractualMaturitiesDetails</Role>
      <ShortName>Investments - Schedule of Amortized Cost and Estimated Fair Value of Investment Securities by Contractual Maturities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>40305 - Disclosure - Investments - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsNarrativeDetails</Role>
      <ShortName>Investments - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>40306 - Disclosure - Investments - Schedule of Securities Related to Unrecognized OTTI (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsScheduleOfSecuritiesRelatedToUnrecognizedOttiDetails</Role>
      <ShortName>Investments - Schedule of Securities Related to Unrecognized OTTI (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>40307 - Disclosure - Investments - Schedule of Other Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureInvestmentsScheduleOfOtherInvestmentsDetails</Role>
      <ShortName>Investments - Schedule of Other Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>40401 - Disclosure - Loans - Schedule of Loan Portfolio Segments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfLoanPortfolioSegmentsDetails</Role>
      <ShortName>Loans - Schedule of Loan Portfolio Segments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>40402 - Disclosure - Loans - Acquired loans and reclassifications (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansAcquiredLoansAndReclassificationsDetails</Role>
      <ShortName>Loans - Acquired loans and reclassifications (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>40403 - Disclosure - Loans - Schedule of Major Portfolio Segment and Non-Classified and Classified Loan Class (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfMajorPortfolioSegmentAndNonClassifiedAndClassifiedLoanClassDetails</Role>
      <ShortName>Loans - Schedule of Major Portfolio Segment and Non-Classified and Classified Loan Class (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>40404 - Disclosure - Loans - Schedule of Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfAllowanceForLoanLossesDetails</Role>
      <ShortName>Loans - Schedule of Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>40405 - Disclosure - Loans - Schedule of Loans Held for Investment and ALL on the basis of Impairment Method (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfLoansHeldForInvestmentAndAllOnBasisOfImpairmentMethodDetails</Role>
      <ShortName>Loans - Schedule of Loans Held for Investment and ALL on the basis of Impairment Method (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>40406 - Disclosure - Loans - Schedule of Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfImpairedLoansDetails</Role>
      <ShortName>Loans - Schedule of Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>40407 - Disclosure - Loans - Schedule of Impaired Loans (Average Recorded Investment in Impaired Loans and Interest Income Recognized) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfImpairedLoansAverageRecordedInvestmentInImpairedLoansAndInterestIncomeRecognizedDetails</Role>
      <ShortName>Loans - Schedule of Impaired Loans (Average Recorded Investment in Impaired Loans and Interest Income Recognized) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>40408 - Disclosure - Loans - Schedule of Transactions Related to Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfTransactionsRelatedToTroubledDebtRestructuringsDetails</Role>
      <ShortName>Loans - Schedule of Transactions Related to Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>40409 - Disclosure - Loans - Schedule of Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfTroubledDebtRestructuringsDetails</Role>
      <ShortName>Loans - Schedule of Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>40410 - Disclosure - Loans - Schedule of Troubled Debt Restructurings that Subsequently Defaulted (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfTroubledDebtRestructuringsThatSubsequentlyDefaultedDetails</Role>
      <ShortName>Loans - Schedule of Troubled Debt Restructurings that Subsequently Defaulted (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>40411 - Disclosure - Loans - Schedule of Nonaccrual Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfNonaccrualLoansDetails</Role>
      <ShortName>Loans - Schedule of Nonaccrual Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>40412 - Disclosure - Loans - Schedule of Aging of Company's Loan Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfAgingOfCompanySLoanPortfolioDetails</Role>
      <ShortName>Loans - Schedule of Aging of Company's Loan Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>40413 - Disclosure - Loans - Schedule Of Loans And Leases Receivable, Related Parties (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLoansScheduleOfLoansAndLeasesReceivableRelatedPartiesDetails</Role>
      <ShortName>Loans - Schedule Of Loans And Leases Receivable, Related Parties (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>40501 - Disclosure - Premises And Equipment - Schedule Of Premises And Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipmentScheduleOfPremisesAndEquipmentDetails</Role>
      <ShortName>Premises And Equipment - Schedule Of Premises And Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>40502 - Disclosure - Premises And Equipment (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipmentNarrativeDetails</Role>
      <ShortName>Premises And Equipment (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosurePremisesAndEquipmentTables</ParentRole>
      <Position>80</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>40601 - Disclosure - Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIntangibleAssetsScheduleOfFiniteLivedIntangibleAssetsDetails</Role>
      <ShortName>Intangible Assets - Schedule of Finite-Lived Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>40602 - Disclosure - Intangible Assets - Schedule Of Expected Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIntangibleAssetsScheduleOfExpectedAmortizationExpenseDetails</Role>
      <ShortName>Intangible Assets - Schedule Of Expected Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>40701 - Disclosure - Deposits - Schedule Of Certificates Of Deposit Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDepositsScheduleOfCertificatesOfDepositPortfolioDetails</Role>
      <ShortName>Deposits - Schedule Of Certificates Of Deposit Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>40702 - Disclosure - Deposits - Schedule Of Interest Expense Allocated To Certificates Of Deposit (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDepositsScheduleOfInterestExpenseAllocatedToCertificatesOfDepositDetails</Role>
      <ShortName>Deposits - Schedule Of Interest Expense Allocated To Certificates Of Deposit (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>40703 - Disclosure - Deposits - Schedule Of Certificates Of Deposit, By Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDepositsScheduleOfCertificatesOfDepositByContractualMaturityDetails</Role>
      <ShortName>Deposits - Schedule Of Certificates Of Deposit, By Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>40801 - Disclosure - Borrowed Funds - Schedule of Securities Sold Under Agreements to Repurchase (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureBorrowedFundsScheduleOfSecuritiesSoldUnderAgreementsToRepurchaseDetails</Role>
      <ShortName>Borrowed Funds - Schedule of Securities Sold Under Agreements to Repurchase (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>40802 - Disclosure - Borrowed Funds - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureBorrowedFundsNarrativeDetails</Role>
      <ShortName>Borrowed Funds - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>40901 - Disclosure - Long-Term Debt - Schedule Of Long-term Debt Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebtScheduleOfLongTermDebtInstrumentsDetails</Role>
      <ShortName>Long-Term Debt - Schedule Of Long-term Debt Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>40902 - Disclosure - Long-Term Debt - Narrative, Part I (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebtNarrativePartIDetails</Role>
      <ShortName>Long-Term Debt - Narrative, Part I (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>40903 - Disclosure - Long-Term Debt - Narrative, Part II (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebtNarrativePartIiDetails</Role>
      <ShortName>Long-Term Debt - Narrative, Part II (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>40904 - Disclosure - Long-Term Debt - Subordinated Notes Payable - Terms (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureLongTermDebtSubordinatedNotesPayableTermsDetails</Role>
      <ShortName>Long-Term Debt - Subordinated Notes Payable - Terms (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>41001 - Disclosure - Derivatives - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivativesNarrativeDetails</Role>
      <ShortName>Derivatives - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>41002 - Disclosure - Derivatives - Schedule of Derivatives Instruments in Statements of Financial Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivativesScheduleOfDerivativesInstrumentsInStatementsOfFinancialPositionDetails</Role>
      <ShortName>Derivatives - Schedule of Derivatives Instruments in Statements of Financial Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>41003 - Disclosure - Derivatives - Schedule of Fair Value of Derivative Financial Instruments and Classification on Condensed Consolidated Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivativesScheduleOfFairValueOfDerivativeFinancialInstrumentsAndClassificationOnCondensedConsolidatedBalanceSheetsDetails</Role>
      <ShortName>Derivatives - Schedule of Fair Value of Derivative Financial Instruments and Classification on Condensed Consolidated Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>41004 - Disclosure - Derivatives - Schedule of Notional Amounts of Outstanding Derivative Positions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureDerivativesScheduleOfNotionalAmountsOfOutstandingDerivativePositionsDetails</Role>
      <ShortName>Derivatives - Schedule of Notional Amounts of Outstanding Derivative Positions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>41101 - Disclosure - Income Taxes - Schedule Of Components Of Income Tax Expense (Benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseBenefitDetails</Role>
      <ShortName>Income Taxes - Schedule Of Components Of Income Tax Expense (Benefit) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>41102 - Disclosure - Income Taxes - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesNarrativeDetails</Role>
      <ShortName>Income Taxes - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>41103 - Disclosure - Income Taxes - Schedule Of Deferred Tax Assets And Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesScheduleOfDeferredTaxAssetsAndLiabilitiesDetails</Role>
      <ShortName>Income Taxes - Schedule Of Deferred Tax Assets And Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>41104 - Disclosure - Income Taxes - Schedule Of Effective Income Tax Rate Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesScheduleOfEffectiveIncomeTaxRateReconciliationDetails</Role>
      <ShortName>Income Taxes - Schedule Of Effective Income Tax Rate Reconciliation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>41105 - Disclosure - Income Taxes - Summary Of Income Tax Examinations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureIncomeTaxesSummaryOfIncomeTaxExaminationsDetails</Role>
      <ShortName>Income Taxes - Summary Of Income Tax Examinations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>41201 - Disclosure - Shareholders' Equity - Schedule Of Stock Reserved For Future Issuance (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureShareholdersEquityScheduleOfStockReservedForFutureIssuanceDetails</Role>
      <ShortName>Shareholders' Equity - Schedule Of Stock Reserved For Future Issuance (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>41202 - Disclosure - Shareholders' Equity - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureShareholdersEquityNarrativeDetails</Role>
      <ShortName>Shareholders' Equity - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>41203 - Disclosure - Shareholders' Equity - Dividends (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureShareholdersEquityDividendsDetails</Role>
      <ShortName>Shareholders' Equity - Dividends (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>41301 - Disclosure - Accumulated Other Comprehensive Income - Reclassifications (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureAccumulatedOtherComprehensiveIncomeReclassificationsDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income - Reclassifications (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>41302 - Disclosure - Accumulated Other Comprehensive Income - AOCI rollforward (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureAccumulatedOtherComprehensiveIncomeAociRollforwardDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income - AOCI rollforward (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>41401 - Disclosure - Earnings per Common Share - Schedule of Weighted Average Shares Outstanding Used in Calculation of Basic and Diluted Loss Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEarningsPerCommonShareScheduleOfWeightedAverageSharesOutstandingUsedInCalculationOfBasicAndDilutedLossPerShareDetails</Role>
      <ShortName>Earnings per Common Share - Schedule of Weighted Average Shares Outstanding Used in Calculation of Basic and Diluted Loss Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>41501 - Disclosure - Employee Benefit And Stock Compensation Plans - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansNarrativeDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>41502 - Disclosure - Employee Benefit And Stock Compensation Plans - Schedule Of Stock Option Valuation Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansScheduleOfStockOptionValuationAssumptionsDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Schedule Of Stock Option Valuation Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>41503 - Disclosure - Employee Benefit And Stock Compensation Plans - Summary Of Changes In Stock Option Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansSummaryOfChangesInStockOptionAwardsDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Summary Of Changes In Stock Option Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>41504 - Disclosure - Employee Benefit And Stock Compensation Plans - Schedule Of Stock Options Outstanding By Exercise Price Range (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansScheduleOfStockOptionsOutstandingByExercisePriceRangeDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Schedule Of Stock Options Outstanding By Exercise Price Range (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>41505 - Disclosure - Employee Benefit And Stock Compensation Plans - Summary Of Changes In Restricted Stock Awards (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansSummaryOfChangesInRestrictedStockAwardsDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Summary Of Changes In Restricted Stock Awards (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>41506 - Disclosure - Employee Benefit And Stock Compensation Plans - Schedule Of Employee Stock Purchase Plan Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansScheduleOfEmployeeStockPurchasePlanActivityDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Schedule Of Employee Stock Purchase Plan Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>41507 - Disclosure - Employee Benefit And Stock Compensation Plans - Narrative II (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureEmployeeBenefitAndStockCompensationPlansNarrativeIiDetails</Role>
      <ShortName>Employee Benefit And Stock Compensation Plans - Narrative II (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>41601 - Disclosure - Commitments and Contingencies - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingenciesNarrativeDetails</Role>
      <ShortName>Commitments and Contingencies - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>41602 - Disclosure - Commitments and Contingencies - Schedule Of Lease Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingenciesScheduleOfLeaseCommitmentsDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule Of Lease Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>41603 - Disclosure - Commitments and Contingencies - Schedule Of Financial Instruments With Off-Balance Sheet Risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCommitmentsAndContingenciesScheduleOfFinancialInstrumentsWithOffBalanceSheetRiskDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule Of Financial Instruments With Off-Balance Sheet Risk (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>116</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>41701 - Disclosure - Regulatory Matters - Schedule of Regulatory Capital Amounts and Ratios of Company and Bank (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureRegulatoryMattersScheduleOfRegulatoryCapitalAmountsAndRatiosOfCompanyAndBankDetails</Role>
      <ShortName>Regulatory Matters - Schedule of Regulatory Capital Amounts and Ratios of Company and Bank (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>41801 - Disclosure - Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsFinancialAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>41802 - Disclosure - Fair Value Measurements - Reconcoliation of the Beginning and Ending Balance of Financial Assets Measured At Fair Value On Recurring Basis Using Level 3 Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsReconcoliationOfBeginningAndEndingBalanceOfFinancialAssetsMeasuredAtFairValueOnRecurringBasisUsingLevel3InputsDetails</Role>
      <ShortName>Fair Value Measurements - Reconcoliation of the Beginning and Ending Balance of Financial Assets Measured At Fair Value On Recurring Basis Using Level 3 Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>119</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>41803 - Disclosure - Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Nonrecurring Basis (OREO and Impaired Loans) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsScheduleOfFinancialAssetsMeasuredAtFairValueOnNonrecurringBasisOreoAndImpairedLoansDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Financial Assets Measured at Fair Value on Nonrecurring Basis (OREO and Impaired Loans) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>41804 - Disclosure - Fair Value Measurements - Schedule of Reconciliation of Fair Value Measurement of Other Real Estate Owned (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsScheduleOfReconciliationOfFairValueMeasurementOfOtherRealEstateOwnedDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Reconciliation of Fair Value Measurement of Other Real Estate Owned (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>41805 - Disclosure - Fair Value Measurements - Summary of Other Real Estate Owned Transactions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsSummaryOfOtherRealEstateOwnedTransactionsDetails</Role>
      <ShortName>Fair Value Measurements - Summary of Other Real Estate Owned Transactions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>41806 - Disclosure - Fair Value Measurements - Schedule of Valuation Process Used to Determine Fair Value Measurement within Level 3 (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsScheduleOfValuationProcessUsedToDetermineFairValueMeasurementWithinLevel3Details</Role>
      <ShortName>Fair Value Measurements - Schedule of Valuation Process Used to Determine Fair Value Measurement within Level 3 (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>123</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R124.htm</HtmlFileName>
      <LongName>41807 - Disclosure - Fair Value Measurements - Schedule of Estimated Fair Value of Other Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureFairValueMeasurementsScheduleOfEstimatedFairValueOfOtherFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value Measurements - Schedule of Estimated Fair Value of Other Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>124</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R125.htm</HtmlFileName>
      <LongName>41901 - Disclosure - Segments - Summary Of Operating And Selected Financial Information By Operating Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSegmentsSummaryOfOperatingAndSelectedFinancialInformationByOperatingSegmentDetails</Role>
      <ShortName>Segments - Summary Of Operating And Selected Financial Information By Operating Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>125</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R126.htm</HtmlFileName>
      <LongName>42001 - Disclosure - Condensed Financial Statements Of Parent Company - Condensed Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompanyCondensedBalanceSheetsDetails</Role>
      <ShortName>Condensed Financial Statements Of Parent Company - Condensed Balance Sheets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>126</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R127.htm</HtmlFileName>
      <LongName>42002 - Disclosure - Condensed Financial Statements Of Parent Company - Condensed Statements Of Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompanyCondensedStatementsOfOperationsDetails</Role>
      <ShortName>Condensed Financial Statements Of Parent Company - Condensed Statements Of Operations (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>127</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R128.htm</HtmlFileName>
      <LongName>42003 - Disclosure - Condensed Financial Statements Of Parent Company - Condensed Statements Of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureCondensedFinancialStatementsOfParentCompanyCondensedStatementsOfCashFlowsDetails</Role>
      <ShortName>Condensed Financial Statements Of Parent Company - Condensed Statements Of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>128</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R129.htm</HtmlFileName>
      <LongName>42101 - Disclosure - Supplemental Financial Data (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSupplementalFinancialDataDetails</Role>
      <ShortName>Supplemental Financial Data (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureSupplementalFinancialDataTables</ParentRole>
      <Position>129</Position>
    </Report>
    <Report instance="cobz-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R130.htm</HtmlFileName>
      <LongName>42201 - Disclosure - Selected Quarterly Financial Data (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cobizfinancial.com/role/DisclosureSelectedQuarterlyFinancialDataDetails</Role>
      <ShortName>Selected Quarterly Financial Data (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cobizfinancial.com/role/DisclosureSelectedQuarterlyFinancialDataUnauditedTables</ParentRole>
      <Position>130</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>cobz-20161231.xml</File>
    <File>cobz-20161231.xsd</File>
    <File>cobz-20161231_cal.xml</File>
    <File>cobz-20161231_def.xml</File>
    <File>cobz-20161231_lab.xml</File>
    <File>cobz-20161231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
