<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.21.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>375</ContextCount>
  <ElementCount>367</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>76</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>9</UnitCount>
  <MyReports>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Consolidated Balance Sheets (Current Period Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-balance-sheets-current-period-unaudited</Role>
      <ShortName>Consolidated Balance Sheets (Current Period Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-balance-sheets-current-period-unaudited-parentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-statements-of-income-unaudited</Role>
      <ShortName>Consolidated Statements of Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Consolidated Statements of Comprehensive Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-statements-of-comprehensive-income-unaudited</Role>
      <ShortName>Consolidated Statements of Comprehensive Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Consolidated Statements of Changes in Shareholders' Equity (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-statements-of-changes-in-shareholders-equity-unaudited</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Statement - Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-statements-of-changes-in-shareholders-equity-unaudited-parentheticals</Role>
      <ShortName>Consolidated Statements of Changes in Shareholders' Equity (Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Statement - Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-consolidated-statements-of-cash-flows-unaudited</Role>
      <ShortName>Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 1 - Basis of Presentation and Reclassifications</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-1-basis-of-presentation-and-reclassifications</Role>
      <ShortName>Note 1 - Basis of Presentation and Reclassifications</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 2 - Authoritative Accounting Guidance</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-2-authoritative-accounting-guidance</Role>
      <ShortName>Note 2 - Authoritative Accounting Guidance</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 3 - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities</Role>
      <ShortName>Note 3 - Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 4 - Loans and Allowance for Loan Losses</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 5 - Legal Proceedings</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-5-legal-proceedings</Role>
      <ShortName>Note 5 - Legal Proceedings</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 6 - Earnings Per Share and Capital Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-6-earnings-per-share-and-capital-transactions</Role>
      <ShortName>Note 6 - Earnings Per Share and Capital Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 7 - Subordinated Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-7-subordinated-debt</Role>
      <ShortName>Note 7 - Subordinated Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 8 - Commitments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments</Role>
      <ShortName>Note 8 - Commitments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 9 - Fair Value of Assets and Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities</Role>
      <ShortName>Note 9 - Fair Value of Assets and Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 10 - Accumulated Other Comprehensive Income (Loss)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss</Role>
      <ShortName>Note 10 - Accumulated Other Comprehensive Income (Loss)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 11 - Post-retirement Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-11-postretirement-obligations</Role>
      <ShortName>Note 11 - Post-retirement Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 12 - Stock Repurchase Program</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-12-stock-repurchase-program</Role>
      <ShortName>Note 12 - Stock Repurchase Program</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 13 - Securities Sold Under Agreements to Repurchase</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-13-securities-sold-under-agreements-to-repurchase</Role>
      <ShortName>Note 13 - Securities Sold Under Agreements to Repurchase</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 14 - Equity Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation</Role>
      <ShortName>Note 14 - Equity Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 15 - Risks and Uncertainties</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-15-risks-and-uncertainties</Role>
      <ShortName>Note 15 - Risks and Uncertainties</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 16 - Business Combination</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-16-business-combination</Role>
      <ShortName>Note 16 - Business Combination</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-2-authoritative-accounting-guidance</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 3 - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-tables</Role>
      <ShortName>Note 3 - Investment Securities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 4 - Loans and Allowance for Loan Losses (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-tables</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 6 - Earnings Per Share and Capital Transactions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-6-earnings-per-share-and-capital-transactions-tables</Role>
      <ShortName>Note 6 - Earnings Per Share and Capital Transactions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-6-earnings-per-share-and-capital-transactions</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 8 - Commitments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-tables</Role>
      <ShortName>Note 8 - Commitments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 9 - Fair Value of Assets and Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities-tables</Role>
      <ShortName>Note 9 - Fair Value of Assets and Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 10 - Accumulated Other Comprehensive Income (Loss) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss-tables</Role>
      <ShortName>Note 10 - Accumulated Other Comprehensive Income (Loss) (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 11 - Post-retirement Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-11-postretirement-obligations-tables</Role>
      <ShortName>Note 11 - Post-retirement Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-11-postretirement-obligations</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 13 - Securities Sold Under Agreements to Repurchase (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-13-securities-sold-under-agreements-to-repurchase-tables</Role>
      <ShortName>Note 13 - Securities Sold Under Agreements to Repurchase (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-13-securities-sold-under-agreements-to-repurchase</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 14 - Equity Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation-tables</Role>
      <ShortName>Note 14 - Equity Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 3 - Investment Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-details-textual</Role>
      <ShortName>Note 3 - Investment Securities (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-tables</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 3 - Investment Securities - Summary of Investment Securities Available-for-sale and Regulatory Stock (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-summary-of-investment-securities-availableforsale-and-regulatory-stock-details</Role>
      <ShortName>Note 3 - Investment Securities - Summary of Investment Securities Available-for-sale and Regulatory Stock (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 3 - Investment Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-amortized-cost-and-fair-value-of-debt-securities-by-contractual-maturity-details</Role>
      <ShortName>Note 3 - Investment Securities - Amortized Cost and Fair Value of Debt Securities by Contractual Maturity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 3 - Investment Securities - Proceeds, Gains and Losses Realized (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-proceeds-gains-and-losses-realized-details</Role>
      <ShortName>Note 3 - Investment Securities - Proceeds, Gains and Losses Realized (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 3 - Investment Securities - Summary of the Fair Value of Available-for-sale Securities with Unrealized Losses and an Aging of Those Unrealized Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-3-investment-securities-summary-of-the-fair-value-of-availableforsale-securities-with-unrealized-losses-and-an-aging-of-those-unrealized-losses-details</Role>
      <ShortName>Note 3 - Investment Securities - Summary of the Fair Value of Available-for-sale Securities with Unrealized Losses and an Aging of Those Unrealized Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 4 - Loans and Allowance for Loan Losses (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-details-textual</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-tables</ParentRole>
      <Position>40</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Composition of Loan Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-composition-of-loan-portfolio-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Composition of Loan Portfolio (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Analysis of Changes in the Allowance for Loan Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-analysis-of-changes-in-the-allowance-for-loan-losses-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Analysis of Changes in the Allowance for Loan Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Summary of Credit Quality Indicators by Internally Assigned Grades (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-summary-of-credit-quality-indicators-by-internally-assigned-grades-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Summary of Credit Quality Indicators by Internally Assigned Grades (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Summary of Consumer Credit Exposure (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-summary-of-consumer-credit-exposure-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Summary of Consumer Credit Exposure (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Summary of Classes of Loans on Non-accrual Status (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-summary-of-classes-of-loans-on-nonaccrual-status-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Summary of Classes of Loans on Non-accrual Status (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Aging Analysis of the Recorded Investment of Past Due Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-aging-analysis-of-the-recorded-investment-of-past-due-loans-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Aging Analysis of the Recorded Investment of Past Due Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 4 - Loans and Allowance for Loan Losses - Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-4-loans-and-allowance-for-loan-losses-impaired-loans-details</Role>
      <ShortName>Note 4 - Loans and Allowance for Loan Losses - Impaired Loans (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 6 - Earnings Per Share and Capital Transactions - Computation of Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-6-earnings-per-share-and-capital-transactions-computation-of-earnings-per-share-details</Role>
      <ShortName>Note 6 - Earnings Per Share and Capital Transactions - Computation of Earnings Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 7 - Subordinated Debt (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-7-subordinated-debt-details-textual</Role>
      <ShortName>Note 7 - Subordinated Debt (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-7-subordinated-debt</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 8 - Commitments (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-details-textual</Role>
      <ShortName>Note 8 - Commitments (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-tables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 8 - Commitments - Summary of Contractual Commitments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-summary-of-contractual-commitments-details</Role>
      <ShortName>Note 8 - Commitments - Summary of Contractual Commitments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 8 - Commitments - Summary of Overdraft Protection (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-summary-of-overdraft-protection-details</Role>
      <ShortName>Note 8 - Commitments - Summary of Overdraft Protection (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>052 - Disclosure - Note 8 - Commitments - Summary of Information Regarding Derivatives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-summary-of-information-regarding-derivatives-details</Role>
      <ShortName>Note 8 - Commitments - Summary of Information Regarding Derivatives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>053 - Disclosure - Note 8 - Commitments - Fair Values of Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-8-commitments-fair-values-of-derivative-instruments-details</Role>
      <ShortName>Note 8 - Commitments - Fair Values of Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>054 - Disclosure - Note 9 - Fair Value of Assets and Liabilities - Assets Reported on the Consolidated Balance Sheets, on a Recurring Basis, at Their Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities-assets-reported-on-the-consolidated-balance-sheets-on-a-recurring-basis-at-their-fair-value-details</Role>
      <ShortName>Note 9 - Fair Value of Assets and Liabilities - Assets Reported on the Consolidated Balance Sheets, on a Recurring Basis, at Their Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>055 - Disclosure - Note 9 - Fair Value of Assets and Liabilities - Quantitative Information About the Level 3 Significant Inputs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities-quantitative-information-about-the-level-3-significant-inputs-details</Role>
      <ShortName>Note 9 - Fair Value of Assets and Liabilities - Quantitative Information About the Level 3 Significant Inputs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>056 - Disclosure - Note 9 - Fair Value of Assets and Liabilities - Carrying Amounts and Fair Values of the Company's Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-9-fair-value-of-assets-and-liabilities-carrying-amounts-and-fair-values-of-the-companys-financial-instruments-details</Role>
      <ShortName>Note 9 - Fair Value of Assets and Liabilities - Carrying Amounts and Fair Values of the Company's Financial Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>057 - Disclosure - Note 10 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss-changes-in-accumulated-other-comprehensive-income-loss-by-component-details</Role>
      <ShortName>Note 10 - Accumulated Other Comprehensive Income (Loss) - Changes in Accumulated Other Comprehensive Income (Loss) by Component (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss-tables</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>058 - Disclosure - Note 10 - Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss-reclassifications-out-of-accumulated-other-comprehensive-income-loss-details</Role>
      <ShortName>Note 10 - Accumulated Other Comprehensive Income (Loss) - Reclassifications Out of Accumulated Other Comprehensive Income (Loss) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-10-accumulated-other-comprehensive-income-loss-tables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>059 - Disclosure - Note 11 - Post-retirement Obligations - Changes in Accumulated Liability (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-11-postretirement-obligations-changes-in-accumulated-liability-details</Role>
      <ShortName>Note 11 - Post-retirement Obligations - Changes in Accumulated Liability (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>060 - Disclosure - Note 12 - Stock Repurchase Program (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-12-stock-repurchase-program-details-textual</Role>
      <ShortName>Note 12 - Stock Repurchase Program (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-12-stock-repurchase-program</ParentRole>
      <Position>61</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>061 - Disclosure - Note 13 - Securities Sold Under Agreements to Repurchase - Repurchase Agreements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-13-securities-sold-under-agreements-to-repurchase-repurchase-agreements-details</Role>
      <ShortName>Note 13 - Securities Sold Under Agreements to Repurchase - Repurchase Agreements (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>062 - Disclosure - Note 14 - Equity Compensation (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation-details-textual</Role>
      <ShortName>Note 14 - Equity Compensation (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation-tables</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>063 - Disclosure - Note 14 - Equity Compensation - Activity Under the Omnibus Equity Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-14-equity-compensation-activity-under-the-omnibus-equity-plan-details</Role>
      <ShortName>Note 14 - Equity Compensation - Activity Under the Omnibus Equity Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="cldb20210630_10q.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>064 - Disclosure - Note 16 - Business Combination (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cortlandbank.com/20210630/role/statement-note-16-business-combination-details-textual</Role>
      <ShortName>Note 16 - Business Combination (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cortlandbank.com/20210630/role/statement-note-16-business-combination</ParentRole>
      <Position>65</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="cldb20210630_10q.htm">cldb20210630_10q.htm</File>
    <File>cldb-20210630.xsd</File>
    <File>cldb-20210630_cal.xml</File>
    <File>cldb-20210630_def.xml</File>
    <File>cldb-20210630_lab.xml</File>
    <File>cldb-20210630_pre.xml</File>
    <File>ex_252802.htm</File>
    <File>ex_252803.htm</File>
    <File>ex_252804.htm</File>
    <File>ex_266715.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2021-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2021</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
