<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.6.0.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>334</ContextCount>
  <ElementCount>619</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>83</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>100000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>100010 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>100020 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>100030 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedStatementsOfIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>100040 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedStatementsOfComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>100050 - Statement - Consolidated Statements of Changes in Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedStatementsOfChangesInShareholdersEquity</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>100060 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/StatementConsolidatedStatementsOfCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>100070 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>100080 - Disclosure - Business Combinations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureBusinessCombinations</Role>
      <ShortName>Business Combinations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>100090 - Disclosure - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecurities</Role>
      <ShortName>Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>100100 - Disclosure - Loans and Allowance for Loan and Lease Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLosses</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>100110 - Disclosure - Premises and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipment</Role>
      <ShortName>Premises and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>100120 - Disclosure - Goodwill and Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssets</Role>
      <ShortName>Goodwill and Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>100130 - Disclosure - Other Real Estate Owned</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwned</Role>
      <ShortName>Other Real Estate Owned</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>100140 - Disclosure - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDeposits</Role>
      <ShortName>Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>100150 - Disclosure - Securities Sold Under Repurchase Agreements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSecuritiesSoldUnderRepurchaseAgreements</Role>
      <ShortName>Securities Sold Under Repurchase Agreements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>100160 - Disclosure - Federal Home Loan Bank Advances</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFederalHomeLoanBankAdvances</Role>
      <ShortName>Federal Home Loan Bank Advances</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>100170 - Disclosure - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLoss</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>100180 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>100190 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureCommitmentsAndContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>100200 - Disclosure - Concentration of Credit Risk</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureConcentrationOfCreditRisk</Role>
      <ShortName>Concentration of Credit Risk</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>100210 - Disclosure - Regulatory Matters And Restrictions On Dividends</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRegulatoryMattersAndRestrictionsOnDividends</Role>
      <ShortName>Regulatory Matters And Restrictions On Dividends</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>100220 - Disclosure - Nonvoting and Series A Preferred Stock and Stock Warrants</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureNonvotingAndSeriesAPreferredStockAndStockWarrants</Role>
      <ShortName>Nonvoting and Series A Preferred Stock and Stock Warrants</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>100230 - Disclosure - Shareholders' Agreement</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureShareholdersAgreement</Role>
      <ShortName>Shareholders' Agreement</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>100240 - Disclosure - Stock Options and Restricted Shares</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedShares</Role>
      <ShortName>Stock Options and Restricted Shares</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>100250 - Disclosure - Employment Contracts</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureEmploymentContracts</Role>
      <ShortName>Employment Contracts</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>100260 - Disclosure - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureEmployeeBenefitPlans</Role>
      <ShortName>Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>100270 - Disclosure - Derivative Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstruments</Role>
      <ShortName>Derivative Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>100280 - Disclosure - Related Party</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRelatedParty</Role>
      <ShortName>Related Party</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>100290 - Disclosure - Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValue</Role>
      <ShortName>Fair Value</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>100300 - Disclosure - Parent Company Only Financial Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformation</Role>
      <ShortName>Parent Company Only Financial Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>100310 - Disclosure - Quarterly Financial Results (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureQuarterlyFinancialResultsUnaudited</Role>
      <ShortName>Quarterly Financial Results (Unaudited)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>100320 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>100330 - Disclosure - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesTables</Role>
      <ShortName>Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>100340 - Disclosure - Business Combinations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureBusinessCombinationsTables</Role>
      <ShortName>Business Combinations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureBusinessCombinations</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>100350 - Disclosure - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesTables</Role>
      <ShortName>Investment Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecurities</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>100360 - Disclosure - Loans and Allowance for Loan and Lease Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesTables</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLosses</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>100370 - Disclosure - Premises and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipmentTables</Role>
      <ShortName>Premises and Equipment (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipment</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>100380 - Disclosure - Goodwill and Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssets</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>100390 - Disclosure - Other Real Estate Owned (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwnedTables</Role>
      <ShortName>Other Real Estate Owned (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwned</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>100400 - Disclosure - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDepositsTables</Role>
      <ShortName>Deposits (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDeposits</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>100410 - Disclosure - Securities Sold Under Repurchase Agreements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSecuritiesSoldUnderRepurchaseAgreementsTables</Role>
      <ShortName>Securities Sold Under Repurchase Agreements (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSecuritiesSoldUnderRepurchaseAgreements</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>100420 - Disclosure - Federal Home Loan Bank Advances (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFederalHomeLoanBankAdvancesTables</Role>
      <ShortName>Federal Home Loan Bank Advances (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFederalHomeLoanBankAdvances</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>100430 - Disclosure - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLossTables</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLoss</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>100440 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxes</ParentRole>
      <Position>45</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>100450 - Disclosure - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureCommitmentsAndContingenciesTables</Role>
      <ShortName>Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureCommitmentsAndContingencies</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>100460 - Disclosure - Regulatory Matters And Restrictions On Dividends (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRegulatoryMattersAndRestrictionsOnDividendsTables</Role>
      <ShortName>Regulatory Matters And Restrictions On Dividends (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRegulatoryMattersAndRestrictionsOnDividends</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>100470 - Disclosure - Stock Options and Restricted Shares (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesTables</Role>
      <ShortName>Stock Options and Restricted Shares (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedShares</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>100480 - Disclosure - Derivative Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstrumentsTables</Role>
      <ShortName>Derivative Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstruments</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>100490 - Disclosure - Related Party (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRelatedPartyTables</Role>
      <ShortName>Related Party (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRelatedParty</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>100500 - Disclosure - Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValueTables</Role>
      <ShortName>Fair Value (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValue</ParentRole>
      <Position>51</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>100510 - Disclosure - Parent Company Only Financial Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformationTables</Role>
      <ShortName>Parent Company Only Financial Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformation</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>100520 - Disclosure - Quarterly Financial Results (Unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureQuarterlyFinancialResultsUnauditedTables</Role>
      <ShortName>Quarterly Financial Results (Unaudited) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureQuarterlyFinancialResultsUnaudited</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>100530 - Disclosure - Summary of Significant Accounting Policies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesAdditionalInformationDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>100540 - Disclosure - Summary of Significant Accounting Policies - Summary of Basic and Diluted Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSummaryOfSignificantAccountingPoliciesSummaryOfBasicAndDilutedEarningsPerShareDetails</Role>
      <ShortName>Summary of Significant Accounting Policies - Summary of Basic and Diluted Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>100550 - Disclosure - Business Combinations - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureBusinessCombinationsAdditionalInformationDetails</Role>
      <ShortName>Business Combinations - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>100560 - Disclosure - Business Combinations - Summary of Consideration Paid for Farmington and Amounts of Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureBusinessCombinationsSummaryOfConsiderationPaidForFarmingtonAndAmountsOfAssetsAcquiredAndLiabilitiesAssumedDetails</Role>
      <ShortName>Business Combinations - Summary of Consideration Paid for Farmington and Amounts of Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>100570 - Disclosure - Investment Securities - Summary of Company's Classification of Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesSummaryOfCompanySClassificationOfSecuritiesDetails</Role>
      <ShortName>Investment Securities - Summary of Company's Classification of Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>100580 - Disclosure - Investment Securities - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesAdditionalInformationDetails</Role>
      <ShortName>Investment Securities - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>100590 - Disclosure - Investment Securities - Summary of Amortized Cost and Fair Value of Debt and Equity Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesSummaryOfAmortizedCostAndFairValueOfDebtAndEquitySecuritiesByContractualMaturityDetails</Role>
      <ShortName>Investment Securities - Summary of Amortized Cost and Fair Value of Debt and Equity Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>100600 - Disclosure - Investment Securities - Summary of Sale of Debt and Equity Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesSummaryOfSaleOfDebtAndEquitySecuritiesDetails</Role>
      <ShortName>Investment Securities - Summary of Sale of Debt and Equity Securities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>100610 - Disclosure - Investment Securities - Summary of Securities with Unrealized Losses Aggregated by Major Security Type and Length of Time in a Continuous Unrealized Loss Position (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureInvestmentSecuritiesSummaryOfSecuritiesWithUnrealizedLossesAggregatedByMajorSecurityTypeAndLengthOfTimeInContinuousUnrealizedLossPositionDetails</Role>
      <ShortName>Investment Securities - Summary of Securities with Unrealized Losses Aggregated by Major Security Type and Length of Time in a Continuous Unrealized Loss Position (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>100620 - Disclosure - Loans and Allowance for Loan And Lease Losses - Summary of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesSummaryOfLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan And Lease Losses - Summary of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>100630 - Disclosure - Loans and Allowance for Loan And Lease Losses - Additional Information (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesAdditionalInformationDetail</Role>
      <ShortName>Loans and Allowance for Loan And Lease Losses - Additional Information (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>100640 - Disclosure - Loans and Allowance for Loan And Lease Losses - Summary of Risk Category of Loans by Applicable Class of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesSummaryOfRiskCategoryOfLoansByApplicableClassOfLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan And Lease Losses - Summary of Risk Category of Loans by Applicable Class of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>100650 - Disclosure - Loans and Allowance for Loan and Lease Losses - Summary of Changes in Allowance for Loan Losses by Loan Classification (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesSummaryOfChangesInAllowanceForLoanLossesByLoanClassificationDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Summary of Changes in Allowance for Loan Losses by Loan Classification (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>100660 - Disclosure - Loans and Allowance for Loan and Lease Losses - Allocation of ALLL with Corresponding Percentage of Loans in Each Category to Total Loans, Net of Deferred Fee (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesAllocationOfALLLWithCorrespondingPercentageOfLoansInEachCategoryToTotalLoansNetOfDeferredFeeDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Allocation of ALLL with Corresponding Percentage of Loans in Each Category to Total Loans, Net of Deferred Fee (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>100670 - Disclosure - Loans and Allowance for Loan and Lease Losses - Summary of Information Related to Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesSummaryOfInformationRelatedToImpairedLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Summary of Information Related to Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>100680 - Disclosure - Loans and Allowance for Loan and Lease Losses - Schedule of Aging of Recorded Investment in Past-due Loans, by Class of Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfAgingOfRecordedInvestmentInPastDueLoansByClassOfLoansDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Schedule of Aging of Recorded Investment in Past-due Loans, by Class of Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>100690 - Disclosure - Loans and Allowance for Loan and Lease Losses - Schedule of Non-Accrual Loans and Troubled Debt Restructurings (TDR) by Class of Loans (Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfNonAccrualLoansAndTroubledDebtRestructuringsTDRByClassOfLoansDetail</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Schedule of Non-Accrual Loans and Troubled Debt Restructurings (TDR) by Class of Loans (Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>100700 - Disclosure - Loans and Allowance for Loan And Lease Losses - Schedule of Presents Loans by Class Modified as TDR (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfPresentsLoansByClassModifiedAsTDRDetails</Role>
      <ShortName>Loans and Allowance for Loan And Lease Losses - Schedule of Presents Loans by Class Modified as TDR (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>100710 - Disclosure - Loans and Allowance for Loan and Lease Losses - Schedule of Loans by Class Modified as TDR for the Payment Default Within Twelve Months(Detail)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfLoansByClassModifiedAsTDRForPaymentDefaultWithinTwelveMonthsDetail</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Schedule of Loans by Class Modified as TDR for the Payment Default Within Twelve Months(Detail)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>100720 - Disclosure - Loans and Allowance for Loan and Lease Losses - Schedule of Accretable Yield or Income Expected to be Collected (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfAccretableYieldOrIncomeExpectedToBeCollectedDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Schedule of Accretable Yield or Income Expected to be Collected (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>100730 - Disclosure - Loans and Allowance for Loan And Lease Losses - Schedule of Components of Direct Financing Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesScheduleOfComponentsOfDirectFinancingLeasesDetails</Role>
      <ShortName>Loans and Allowance for Loan And Lease Losses - Schedule of Components of Direct Financing Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>100740 - Disclosure - Loans and Allowance for Loan and Lease Losses - Summary of Future Minimum Lease Payments Receivable under Direct Financing Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureLoansAndAllowanceForLoanAndLeaseLossesSummaryOfFutureMinimumLeasePaymentsReceivableUnderDirectFinancingLeasesDetails</Role>
      <ShortName>Loans and Allowance for Loan and Lease Losses - Summary of Future Minimum Lease Payments Receivable under Direct Financing Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>100750 - Disclosure - Premises and Equipment - Summary of Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipmentSummaryOfPremisesAndEquipmentDetails</Role>
      <ShortName>Premises and Equipment - Summary of Premises and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>100760 - Disclosure - Premises and Equipment - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipmentAdditionalInformationDetails</Role>
      <ShortName>Premises and Equipment - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>100770 - Disclosure - Premises and Equipment - Summary of Future Minimum Payments under Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosurePremisesAndEquipmentSummaryOfFutureMinimumPaymentsUnderOperatingLeasesDetails</Role>
      <ShortName>Premises and Equipment - Summary of Future Minimum Payments under Operating Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>100780 - Disclosure - Goodwill And Intangible Assets - Summary of Change In Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsSummaryOfChangeInGoodwillDetails</Role>
      <ShortName>Goodwill And Intangible Assets - Summary of Change In Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>100790 - Disclosure - Goodwill And Intangible Assets - Summary of Acquired Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsSummaryOfAcquiredIntangibleAssetsDetails</Role>
      <ShortName>Goodwill And Intangible Assets - Summary of Acquired Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>100800 - Disclosure - Goodwill And Intangible Assets - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsAdditionalInformationDetails</Role>
      <ShortName>Goodwill And Intangible Assets - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>100810 - Disclosure - Goodwill And Intangible Assets - Summary of Estimated Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureGoodwillAndIntangibleAssetsSummaryOfEstimatedAmortizationExpenseDetails</Role>
      <ShortName>Goodwill And Intangible Assets - Summary of Estimated Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>100820 - Disclosure - Other Real Estate Owned - Summary of Other Real Estate Owned Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwnedSummaryOfOtherRealEstateOwnedActivityDetails</Role>
      <ShortName>Other Real Estate Owned - Summary of Other Real Estate Owned Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>100830 - Disclosure - Other Real Estate Owned - Summary of Valuation Allowance Activity in Other Real Estate Owned (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwnedSummaryOfValuationAllowanceActivityInOtherRealEstateOwnedDetails</Role>
      <ShortName>Other Real Estate Owned - Summary of Valuation Allowance Activity in Other Real Estate Owned (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>100840 - Disclosure - Other Real Estate Owned - Summary of Expenses Related to Other Real Estate Owned (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureOtherRealEstateOwnedSummaryOfExpensesRelatedToOtherRealEstateOwnedDetails</Role>
      <ShortName>Other Real Estate Owned - Summary of Expenses Related to Other Real Estate Owned (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>100850 - Disclosure - Deposits - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDepositsAdditionalInformationDetails</Role>
      <ShortName>Deposits - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>100860 - Disclosure - Deposits - Scheduled Maturities of Time Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDepositsScheduledMaturitiesOfTimeDepositsDetails</Role>
      <ShortName>Deposits - Scheduled Maturities of Time Deposits (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>100870 - Disclosure - Securities Sold Under Repurchase Agreements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSecuritiesSoldUnderRepurchaseAgreementsAdditionalInformationDetails</Role>
      <ShortName>Securities Sold Under Repurchase Agreements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>100880 - Disclosure - Securities Sold Under Repurchase Agreements - Summary of Information Concerning Securities Sold Under Repurchase Agreements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureSecuritiesSoldUnderRepurchaseAgreementsSummaryOfInformationConcerningSecuritiesSoldUnderRepurchaseAgreementsDetails</Role>
      <ShortName>Securities Sold Under Repurchase Agreements - Summary of Information Concerning Securities Sold Under Repurchase Agreements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>100890 - Disclosure - Federal Home Loan Bank Advances - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFederalHomeLoanBankAdvancesAdditionalInformationDetails</Role>
      <ShortName>Federal Home Loan Bank Advances - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>100900 - Disclosure - Federal Home Loan Bank Advances - Summary of Contractual Maturities and Average Effective Rates of Outstanding Advances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFederalHomeLoanBankAdvancesSummaryOfContractualMaturitiesAndAverageEffectiveRatesOfOutstandingAdvancesDetails</Role>
      <ShortName>Federal Home Loan Bank Advances - Summary of Contractual Maturities and Average Effective Rates of Outstanding Advances (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>100910 - Disclosure - Accumulated Other Comprehensive Income (Loss) - Summary of Changes In Accumulated Other Comprehensive Income (Loss) By Component, Net of Tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLossSummaryOfChangesInAccumulatedOtherComprehensiveIncomeLossByComponentNetOfTaxDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) - Summary of Changes In Accumulated Other Comprehensive Income (Loss) By Component, Net of Tax (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLossTables</ParentRole>
      <Position>92</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>100920 - Disclosure - Accumulated Other Comprehensive Income (Loss) - Summary of Significant Amounts Reclassified out off Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLossSummaryOfSignificantAmountsReclassifiedOutOffAccumulatedOtherComprehensiveIncomeLossDetails</Role>
      <ShortName>Accumulated Other Comprehensive Income (Loss) - Summary of Significant Amounts Reclassified out off Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureAccumulatedOtherComprehensiveIncomeLossTables</ParentRole>
      <Position>93</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>100930 - Disclosure - Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxesScheduleOfComponentsOfIncomeTaxExpenseBenefitDetails</Role>
      <ShortName>Income Taxes - Schedule of Components of Income Tax Expense (Benefit) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>100940 - Disclosure - Income Taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income Taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>100950 - Disclosure - Income Taxes - Schedule of Reconciliation of Actual Income Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxesScheduleOfReconciliationOfActualIncomeTaxExpenseDetails</Role>
      <ShortName>Income Taxes - Schedule of Reconciliation of Actual Income Tax Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>100960 - Disclosure - Income Taxes - Schedule of Deferred Taxes (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureIncomeTaxesScheduleOfDeferredTaxesDetails</Role>
      <ShortName>Income Taxes - Schedule of Deferred Taxes (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>100970 - Disclosure - Commitments and Contingencies - Schedule of Financial Instruments Representing Credit Risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureCommitmentsAndContingenciesScheduleOfFinancialInstrumentsRepresentingCreditRiskDetails</Role>
      <ShortName>Commitments and Contingencies - Schedule of Financial Instruments Representing Credit Risk (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>100980 - Disclosure - Concentration of Credit Risk - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureConcentrationOfCreditRiskAdditionalInformationDetails</Role>
      <ShortName>Concentration of Credit Risk - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>100990 - Disclosure - Regulatory Matters And Restrictions On Dividends - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRegulatoryMattersAndRestrictionsOnDividendsAdditionalInformationDetails</Role>
      <ShortName>Regulatory Matters And Restrictions On Dividends - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>101000 - Disclosure - Regulatory Matters And Restrictions On Dividends - Schedule of Capital Amounts and Ratios (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRegulatoryMattersAndRestrictionsOnDividendsScheduleOfCapitalAmountsAndRatiosDetails</Role>
      <ShortName>Regulatory Matters And Restrictions On Dividends - Schedule of Capital Amounts and Ratios (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>101010 - Disclosure - Nonvoting and Series A Preferred Stock and Stock Warrants - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureNonvotingAndSeriesAPreferredStockAndStockWarrantsAdditionalInformationDetails</Role>
      <ShortName>Nonvoting and Series A Preferred Stock and Stock Warrants - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>101020 - Disclosure - Shareholders' Agreement - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureShareholdersAgreementAdditionalInformationDetails</Role>
      <ShortName>Shareholders' Agreement - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>101030 - Disclosure - Stock Options and Restricted Shares - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesAdditionalInformationDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>101040 - Disclosure - Stock Options and Restricted Shares - Summary of Company Recognized Stock-Based Compensation Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesSummaryOfCompanyRecognizedStockBasedCompensationExpenseDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Summary of Company Recognized Stock-Based Compensation Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>101050 - Disclosure - Stock Options and Restricted Shares - Summary of Changes in Company's Nonvested Restricted Shares (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesSummaryOfChangesInCompanySNonvestedRestrictedSharesDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Summary of Changes in Company's Nonvested Restricted Shares (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>101060 - Disclosure - Stock Options and Restricted Shares - Summary of Fair Value of Options Granted Using Weighted Average Assumptions (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesSummaryOfFairValueOfOptionsGrantedUsingWeightedAverageAssumptionsDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Summary of Fair Value of Options Granted Using Weighted Average Assumptions (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>101070 - Disclosure - Stock Options and Restricted Shares - Summary of Activity in Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesSummaryOfActivityInStockOptionsDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Summary of Activity in Stock Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>101080 - Disclosure - Stock Options and Restricted Shares - Information Related to Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureStockOptionsAndRestrictedSharesInformationRelatedToStockOptionsDetails</Role>
      <ShortName>Stock Options and Restricted Shares - Information Related to Stock Options (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>101090 - Disclosure - Employee Benefit Plans- Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureEmployeeBenefitPlansAdditionalInformationDetails</Role>
      <ShortName>Employee Benefit Plans- Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>101100 - Disclosure - Derivative Instruments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstrumentsAdditionalInformationDetails</Role>
      <ShortName>Derivative Instruments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>101110 - Disclosure - Derivative Instruments - Summary of Interest-Rate Swaps Designated as Cash Flow Hedges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstrumentsSummaryOfInterestRateSwapsDesignatedAsCashFlowHedgesDetails</Role>
      <ShortName>Derivative Instruments - Summary of Interest-Rate Swaps Designated as Cash Flow Hedges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>101120 - Disclosure - Derivative Instruments - Summary of Customer Related Interest Rate Swaps (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureDerivativeInstrumentsSummaryOfCustomerRelatedInterestRateSwapsDetails</Role>
      <ShortName>Derivative Instruments - Summary of Customer Related Interest Rate Swaps (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>101130 - Disclosure - Related Party - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRelatedPartyAdditionalInformationDetails</Role>
      <ShortName>Related Party - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>101140 - Disclosure - Related Party - Schedule of Related Party Transactions Activity within Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureRelatedPartyScheduleOfRelatedPartyTransactionsActivityWithinLoansDetails</Role>
      <ShortName>Related Party - Schedule of Related Party Transactions Activity within Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>101150 - Disclosure - Fair Value - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValueSummaryOfAssetsAndLiabilitiesMeasuredAtFairValueOnRecurringBasisDetails</Role>
      <ShortName>Fair Value - Summary of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>116</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>101160 - Disclosure - Fair Value - Summary of Assets Measured at Fair Value on a Nonrecurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValueSummaryOfAssetsMeasuredAtFairValueOnNonrecurringBasisDetails</Role>
      <ShortName>Fair Value - Summary of Assets Measured at Fair Value on a Nonrecurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R118.htm</HtmlFileName>
      <LongName>101170 - Disclosure - Fair Value - Summary of Quantitative Information About Level 3 Fair Value Measurements for Assets Measured at Fair Value on a Non-Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValueSummaryOfQuantitativeInformationAboutLevel3FairValueMeasurementsForAssetsMeasuredAtFairValueOnNonRecurringBasisDetails</Role>
      <ShortName>Fair Value - Summary of Quantitative Information About Level 3 Fair Value Measurements for Assets Measured at Fair Value on a Non-Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>118</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R119.htm</HtmlFileName>
      <LongName>101180 - Disclosure - Fair Value - Summary of Carrying Value and Fair Values of the Bank's Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureFairValueSummaryOfCarryingValueAndFairValuesOfBankSFinancialInstrumentsDetails</Role>
      <ShortName>Fair Value - Summary of Carrying Value and Fair Values of the Bank's Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>119</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R120.htm</HtmlFileName>
      <LongName>101190 - Disclosure - Parent Company Only Financial Information - Condensed Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformationCondensedBalanceSheetDetails</Role>
      <ShortName>Parent Company Only Financial Information - Condensed Balance Sheet (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>120</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R121.htm</HtmlFileName>
      <LongName>101200 - Disclosure - Parent Company Only Financial Information - Condensed Income Statement (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformationCondensedIncomeStatementDetails</Role>
      <ShortName>Parent Company Only Financial Information - Condensed Income Statement (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>121</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R122.htm</HtmlFileName>
      <LongName>101210 - Disclosure - Parent Company Only Financial Information - Condensed Statement of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureParentCompanyOnlyFinancialInformationCondensedStatementOfCashFlowsDetails</Role>
      <ShortName>Parent Company Only Financial Information - Condensed Statement of Cash Flows (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>122</Position>
    </Report>
    <Report instance="cstr-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R123.htm</HtmlFileName>
      <LongName>101220 - Disclosure - Quarterly Financial Results (Unaudited) - Summary of Quarterly Financial Results (Unaudited) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureQuarterlyFinancialResultsUnauditedSummaryOfQuarterlyFinancialResultsUnauditedDetails</Role>
      <ShortName>Quarterly Financial Results (Unaudited) - Summary of Quarterly Financial Results (Unaudited) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://ir.capstarbank.com/20161231/taxonomy/role/DisclosureQuarterlyFinancialResultsUnauditedTables</ParentRole>
      <Position>123</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>cstr-20161231.xml</File>
    <File>cstr-20161231.xsd</File>
    <File>cstr-20161231_cal.xml</File>
    <File>cstr-20161231_def.xml</File>
    <File>cstr-20161231_lab.xml</File>
    <File>cstr-20161231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
