<?xml version='1.0' encoding='UTF-8'?>
<FilingSummary>
  <Version>3.6.0.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>616</ContextCount>
  <ElementCount>694</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>129</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>4</UnitCount>
  <MyReports>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>000 - Document - Document And Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-balance-sheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Consolidated Balance Sheets (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-balance-sheets-parentheticals</Role>
      <ShortName>Consolidated Balance Sheets (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Consolidated Statements of Operations and Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-statements-of-operations-and-comprehensive-income</Role>
      <ShortName>Consolidated Statements of Operations and Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Consolidated Statements of Changes in Stockholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-statements-of-changes-in-stockholders-equity</Role>
      <ShortName>Consolidated Statements of Changes in Stockholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Consolidated Statements of Changes in Stockholders' Equity (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-statements-of-changes-in-stockholders-equity-parentheticals</Role>
      <ShortName>Consolidated Statements of Changes in Stockholders' Equity (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-consolidated-statements-of-cash-flows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Disclosure - Note 1 - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-1-summary-of-significant-accounting-policies</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 2 - Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-2-acquisition</Role>
      <ShortName>Note 2 - Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 3 - Cash and Cash Equivalents</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-3-cash-and-cash-equivalents</Role>
      <ShortName>Note 3 - Cash and Cash Equivalents</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 4 - Investment Securities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities</Role>
      <ShortName>Note 4 - Investment Securities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 5 - Loans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans</Role>
      <ShortName>Note 5 - Loans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-6-investments-in-affordable-housing-and-alternative-energy-partnerships</Role>
      <ShortName>Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 7 - Premises and Equipment</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-7-premises-and-equipment</Role>
      <ShortName>Note 7 - Premises and Equipment</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Note 8 - Deposits</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits</Role>
      <ShortName>Note 8 - Deposits</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 9 - Borrowed Funds</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-9-borrowed-funds</Role>
      <ShortName>Note 9 - Borrowed Funds</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 10 - Capital Resources</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-10-capital-resources</Role>
      <ShortName>Note 10 - Capital Resources</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 11 - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes</Role>
      <ShortName>Note 11 - Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 12 - Stockholders' Equity and Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-12-stockholders-equity-and-earnings-per-share</Role>
      <ShortName>Note 12 - Stockholders' Equity and Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 13 - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies</Role>
      <ShortName>Note 13 - Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 14 - Financial Derivatives</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-14-financial-derivatives</Role>
      <ShortName>Note 14 - Financial Derivatives</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 15 - Fair Value Measurements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-15-fair-value-measurements</Role>
      <ShortName>Note 15 - Fair Value Measurements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 16 - Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-16-fair-value-of-financial-instruments</Role>
      <ShortName>Note 16 - Fair Value of Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 17 - Employee Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-17-employee-benefit-plans</Role>
      <ShortName>Note 17 - Employee Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 18 - Equity Incentive Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans</Role>
      <ShortName>Note 18 - Equity Incentive Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 20 - Dividend Reinvestment Plan</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-20-dividend-reinvestment-plan</Role>
      <ShortName>Note 20 - Dividend Reinvestment Plan</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 21 - Regulatory Matters</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-21-regulatory-matters</Role>
      <ShortName>Note 21 - Regulatory Matters</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 22 - Balance Sheet Offsetting</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-22-balance-sheet-offsetting</Role>
      <ShortName>Note 22 - Balance Sheet Offsetting</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Document - Note 23 - Quarterly Results of Operations (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-23-quarterly-results-of-operations-unaudited</Role>
      <ShortName>Note 23 - Quarterly Results of Operations (Unaudited)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 24 - Subsequent Events</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-24-subsequent-events</Role>
      <ShortName>Note 24 - Subsequent Events</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 1 - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-1-summary-of-significant-accounting-policies-tables</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>33</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 2 - Acquisition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-2-acquisition-tables</Role>
      <ShortName>Note 2 - Acquisition (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 4 - Investment Securities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities-tables</Role>
      <ShortName>Note 4 - Investment Securities (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 5 - Loans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-tables</Role>
      <ShortName>Note 5 - Loans (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 7 - Premises and Equipment (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-7-premises-and-equipment-tables</Role>
      <ShortName>Note 7 - Premises and Equipment (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 8 - Deposits (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits-tables</Role>
      <ShortName>Note 8 - Deposits (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 9 - Borrowed Funds (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-9-borrowed-funds-tables</Role>
      <ShortName>Note 9 - Borrowed Funds (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 10 - Capital Resources (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-10-capital-resources-tables</Role>
      <ShortName>Note 10 - Capital Resources (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 11 - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes-tables</Role>
      <ShortName>Note 11 - Income Taxes (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>041 - Disclosure - Note 12 - Stockholders' Equity and Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-12-stockholders-equity-and-earnings-per-share-tables</Role>
      <ShortName>Note 12 - Stockholders' Equity and Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>042 - Disclosure - Note 13 - Commitments and Contingencies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies-tables</Role>
      <ShortName>Note 13 - Commitments and Contingencies (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>043 - Disclosure - Note 15 - Fair Value Measurements (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-15-fair-value-measurements-tables</Role>
      <ShortName>Note 15 - Fair Value Measurements (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>044 - Disclosure - Note 16 - Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-16-fair-value-of-financial-instruments-tables</Role>
      <ShortName>Note 16 - Fair Value of Financial Instruments (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>045 - Disclosure - Note 18 - Equity Incentive Plans (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans-tables</Role>
      <ShortName>Note 18 - Equity Incentive Plans (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>046 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp-tables</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>047 - Disclosure - Note 21 - Regulatory Matters (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-21-regulatory-matters-tables</Role>
      <ShortName>Note 21 - Regulatory Matters (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>048 - Disclosure - Note 22 - Balance Sheet Offsetting (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-22-balance-sheet-offsetting-tables</Role>
      <ShortName>Note 22 - Balance Sheet Offsetting (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>049 - Disclosure - Note 23 - Quarterly Results of Operations (Unaudited) (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-23-quarterly-results-of-operations-unaudited-tables</Role>
      <ShortName>Note 23 - Quarterly Results of Operations (Unaudited) (Tables)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>050 - Disclosure - Note 1 - Summary of Significant Accounting Policies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-1-summary-of-significant-accounting-policies-details-textual</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>051 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-1-summary-of-significant-accounting-policies-estimated-useful-lives-of-assets-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Estimated Useful Lives of Assets (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>052 - Disclosure - Note 2 - Acquisition (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-2-acquisition-details-textual</Role>
      <ShortName>Note 2 - Acquisition (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>053 - Disclosure - Note 2 - Acquisition - Fair Value of Assets and Liabilities Acquired (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-2-acquisition-fair-value-of-assets-and-liabilities-acquired-details</Role>
      <ShortName>Note 2 - Acquisition - Fair Value of Assets and Liabilities Acquired (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>054 - Disclosure - Note 3 - Cash and Cash Equivalents (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-3-cash-and-cash-equivalents-details-textual</Role>
      <ShortName>Note 3 - Cash and Cash Equivalents (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>055 - Disclosure - Note 4 - Investment Securities (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities-details-textual</Role>
      <ShortName>Note 4 - Investment Securities (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>056 - Disclosure - Note 4 - Investment Securities - Investment Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities-investment-securities-details</Role>
      <ShortName>Note 4 - Investment Securities - Investment Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>057 - Disclosure - Note 4 - Investment Securities - Investments by Contractual Maturity Date (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities-investments-by-contractual-maturity-date-details</Role>
      <ShortName>Note 4 - Investment Securities - Investments by Contractual Maturity Date (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>058 - Disclosure - Note 4 - Investment Securities - Temporarily Impaired Securities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-4-investment-securities-temporarily-impaired-securities-details</Role>
      <ShortName>Note 4 - Investment Securities - Temporarily Impaired Securities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>059 - Disclosure - Note 5 - Loans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-details-textual</Role>
      <ShortName>Note 5 - Loans (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>060 - Disclosure - Note 5 - Loans - Components of Loans in Consolidated Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-components-of-loans-in-consolidated-balance-sheets-details</Role>
      <ShortName>Note 5 - Loans - Components of Loans in Consolidated Balance Sheets (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>061 - Disclosure - Note 5 - Loans - Loans to Related Parties (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-loans-to-related-parties-details</Role>
      <ShortName>Note 5 - Loans - Loans to Related Parties (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>062 - Disclosure - Note 5 - Loans - Impaired Loans and Related Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-impaired-loans-and-related-allowance-for-credit-losses-details</Role>
      <ShortName>Note 5 - Loans - Impaired Loans and Related Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>063 - Disclosure - Note 5 - Loans - Average Balance and Interest Income Recognized Related to Impaired Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-average-balance-and-interest-income-recognized-related-to-impaired-loans-details</Role>
      <ShortName>Note 5 - Loans - Average Balance and Interest Income Recognized Related to Impaired Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>064 - Disclosure - Note 5 - Loans - Non-accrual Loans (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-nonaccrual-loans-details</Role>
      <ShortName>Note 5 - Loans - Non-accrual Loans (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>065 - Disclosure - Note 5 - Loans - Aging of Loan Portfolio (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-aging-of-loan-portfolio-details</Role>
      <ShortName>Note 5 - Loans - Aging of Loan Portfolio (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>066 - Disclosure - Note 5 - Loans - Troubled Debt Restructuring (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-troubled-debt-restructuring-details</Role>
      <ShortName>Note 5 - Loans - Troubled Debt Restructuring (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>067 - Disclosure - Note 5 - Loans - Accruing Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-accruing-troubled-debt-restructurings-details</Role>
      <ShortName>Note 5 - Loans - Accruing Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>068 - Disclosure - Note 5 - Loans - Non-accrual Troubled Debt Restructurings (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-nonaccrual-troubled-debt-restructurings-details</Role>
      <ShortName>Note 5 - Loans - Non-accrual Troubled Debt Restructurings (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>069 - Disclosure - Note 5 - Loans - Troubled Debt Restructuring Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-troubled-debt-restructuring-activity-details</Role>
      <ShortName>Note 5 - Loans - Troubled Debt Restructuring Activity (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>070 - Disclosure - Note 5 - Loans - Portfolio by Risk Rating (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-portfolio-by-risk-rating-details</Role>
      <ShortName>Note 5 - Loans - Portfolio by Risk Rating (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>071 - Disclosure - Note 5 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-allowance-for-loan-losses-by-portfolio-segment-and-based-on-impairment-method-details</Role>
      <ShortName>Note 5 - Loans - Allowance for Loan Losses by Portfolio Segment and Based on Impairment Method (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>072 - Disclosure - Note 5 - Loans - Allowance for Loan Losses by Portfolio Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-allowance-for-loan-losses-by-portfolio-segment-details</Role>
      <ShortName>Note 5 - Loans - Allowance for Loan Losses by Portfolio Segment (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>073 - Disclosure - Note 5 - Loans - Activity in the Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-5-loans-activity-in-the-allowance-for-credit-losses-details</Role>
      <ShortName>Note 5 - Loans - Activity in the Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>74</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>074 - Disclosure - Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-6-investments-in-affordable-housing-and-alternative-energy-partnerships-details-textual</Role>
      <ShortName>Note 6 - Investments in Affordable Housing and Alternative Energy Partnerships (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>075 - Disclosure - Note 7 - Premises and Equipment (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-7-premises-and-equipment-details-textual</Role>
      <ShortName>Note 7 - Premises and Equipment (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>076 - Disclosure - Note 7 - Premises and Equipment - Premises and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-7-premises-and-equipment-premises-and-equipment-details</Role>
      <ShortName>Note 7 - Premises and Equipment - Premises and Equipment (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>077 - Disclosure - Note 8 - Deposits (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits-details-textual</Role>
      <ShortName>Note 8 - Deposits (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>78</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R79.htm</HtmlFileName>
      <LongName>078 - Disclosure - Note 8 - Deposits - Deposit Balances (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits-deposit-balances-details</Role>
      <ShortName>Note 8 - Deposits - Deposit Balances (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R80.htm</HtmlFileName>
      <LongName>079 - Disclosure - Note 8 - Deposits - Time Deposit Maturities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits-time-deposit-maturities-details</Role>
      <ShortName>Note 8 - Deposits - Time Deposit Maturities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>80</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R81.htm</HtmlFileName>
      <LongName>080 - Disclosure - Note 8 - Deposits - Interest Expense on Time Deposits (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-8-deposits-interest-expense-on-time-deposits-details</Role>
      <ShortName>Note 8 - Deposits - Interest Expense on Time Deposits (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>81</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R82.htm</HtmlFileName>
      <LongName>081 - Disclosure - Note 9 - Borrowed Funds (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-9-borrowed-funds-details-textual</Role>
      <ShortName>Note 9 - Borrowed Funds (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>82</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R83.htm</HtmlFileName>
      <LongName>082 - Disclosure - Note 9 - Borrowed Funds - Comparative Data for Securities Sold Under Agreements to Repurchase (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-9-borrowed-funds-comparative-data-for-securities-sold-under-agreements-to-repurchase-details</Role>
      <ShortName>Note 9 - Borrowed Funds - Comparative Data for Securities Sold Under Agreements to Repurchase (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>83</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R84.htm</HtmlFileName>
      <LongName>083 - Disclosure - Note 10 - Capital Resources (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-10-capital-resources-details-textual</Role>
      <ShortName>Note 10 - Capital Resources (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>84</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R85.htm</HtmlFileName>
      <LongName>084 - Disclosure - Note 10 - Capital Resources - Outstanding Junior Subordinated Notes (Details)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-10-capital-resources-outstanding-junior-subordinated-notes-details</Role>
      <ShortName>Note 10 - Capital Resources - Outstanding Junior Subordinated Notes (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>85</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R86.htm</HtmlFileName>
      <LongName>085 - Disclosure - Note 11 - Income Taxes (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes-details-textual</Role>
      <ShortName>Note 11 - Income Taxes (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>86</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R87.htm</HtmlFileName>
      <LongName>086 - Disclosure - Note 11 - Income Taxes - Components of Income Tax Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes-components-of-income-tax-expense-details</Role>
      <ShortName>Note 11 - Income Taxes - Components of Income Tax Expense (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>87</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R88.htm</HtmlFileName>
      <LongName>087 - Disclosure - Note 11 - Income Taxes - Deferred Tax Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes-deferred-tax-assets-and-liabilities-details</Role>
      <ShortName>Note 11 - Income Taxes - Deferred Tax Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>88</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R89.htm</HtmlFileName>
      <LongName>088 - Disclosure - Note 11 - Income Taxes - Income Tax Reconciliation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-11-income-taxes-income-tax-reconciliation-details</Role>
      <ShortName>Note 11 - Income Taxes - Income Tax Reconciliation (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>89</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R90.htm</HtmlFileName>
      <LongName>089 - Disclosure - Note 12 - Stockholders' Equity and Earnings Per Share (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-12-stockholders-equity-and-earnings-per-share-details-textual</Role>
      <ShortName>Note 12 - Stockholders' Equity and Earnings Per Share (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>90</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R91.htm</HtmlFileName>
      <LongName>090 - Disclosure - Note 12 - Stockholders' Equity and Earnings Per Share - Accumulated Other Comprehensive Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-12-stockholders-equity-and-earnings-per-share-accumulated-other-comprehensive-income-details</Role>
      <ShortName>Note 12 - Stockholders' Equity and Earnings Per Share - Accumulated Other Comprehensive Income (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>91</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R92.htm</HtmlFileName>
      <LongName>091 - Disclosure - Note 12 - Stockholders' Equity and Earnings Per Share - Earnings Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-12-stockholders-equity-and-earnings-per-share-earnings-per-share-details</Role>
      <ShortName>Note 12 - Stockholders' Equity and Earnings Per Share - Earnings Per Share (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>92</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R93.htm</HtmlFileName>
      <LongName>092 - Disclosure - Note 13 - Commitments and Contingencies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies-details-textual</Role>
      <ShortName>Note 13 - Commitments and Contingencies (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>93</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R94.htm</HtmlFileName>
      <LongName>093 - Disclosure - Note 13 - Commitments and Contingencies - Financial Instruments With Off-balance Sheet Risk (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies-financial-instruments-with-offbalance-sheet-risk-details</Role>
      <ShortName>Note 13 - Commitments and Contingencies - Financial Instruments With Off-balance Sheet Risk (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>94</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R95.htm</HtmlFileName>
      <LongName>094 - Disclosure - Note 13 - Commitments and Contingencies - Future Payments Under Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies-future-payments-under-operating-leases-details</Role>
      <ShortName>Note 13 - Commitments and Contingencies - Future Payments Under Operating Leases (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>95</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R96.htm</HtmlFileName>
      <LongName>095 - Disclosure - Note 13 - Commitments and Contingencies - Future Rental Income Under Operating Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-13-commitments-and-contingencies-future-rental-income-under-operating-leases-details</Role>
      <ShortName>Note 13 - Commitments and Contingencies - Future Rental Income Under Operating Leases (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>96</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R97.htm</HtmlFileName>
      <LongName>096 - Disclosure - Note 14 - Financial Derivatives (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-14-financial-derivatives-details-textual</Role>
      <ShortName>Note 14 - Financial Derivatives (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>97</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R98.htm</HtmlFileName>
      <LongName>097 - Disclosure - Note 15 - Fair Value Measurements (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-15-fair-value-measurements-details-textual</Role>
      <ShortName>Note 15 - Fair Value Measurements (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>98</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R99.htm</HtmlFileName>
      <LongName>098 - Disclosure - Note 15 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-15-fair-value-measurements-assets-and-liabilities-measured-at-fair-value-on-a-recurring-basis-details</Role>
      <ShortName>Note 15 - Fair Value Measurements - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>99</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R100.htm</HtmlFileName>
      <LongName>099 - Disclosure - Note 15 - Fair Value Measurements - Financial Assets and Liabilities Measured On a Non-recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-15-fair-value-measurements-financial-assets-and-liabilities-measured-on-a-nonrecurring-basis-details</Role>
      <ShortName>Note 15 - Fair Value Measurements - Financial Assets and Liabilities Measured On a Non-recurring Basis (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>100</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R101.htm</HtmlFileName>
      <LongName>100 - Disclosure - Note 16 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-16-fair-value-of-financial-instruments-fair-value-of-financial-instruments-details</Role>
      <ShortName>Note 16 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>101</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R102.htm</HtmlFileName>
      <LongName>101 - Disclosure - Note 16 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-16-fair-value-of-financial-instruments-fair-value-hierarchy-of-financial-instruments-details</Role>
      <ShortName>Note 16 - Fair Value of Financial Instruments - Fair Value Hierarchy of Financial Instruments (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>102</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R103.htm</HtmlFileName>
      <LongName>102 - Disclosure - Note 17 - Employee Benefit Plans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-17-employee-benefit-plans-details-textual</Role>
      <ShortName>Note 17 - Employee Benefit Plans (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>103</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R104.htm</HtmlFileName>
      <LongName>103 - Disclosure - Note 18 - Equity Incentive Plans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans-details-textual</Role>
      <ShortName>Note 18 - Equity Incentive Plans (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>104</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R105.htm</HtmlFileName>
      <LongName>104 - Disclosure - Note 18 - Equity Incentive Plans - Stock Options (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans-stock-options-details</Role>
      <ShortName>Note 18 - Equity Incentive Plans - Stock Options (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>105</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R106.htm</HtmlFileName>
      <LongName>105 - Disclosure - Note 18 - Equity Incentive Plans - Restricted Stock Units (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans-restricted-stock-units-details</Role>
      <ShortName>Note 18 - Equity Incentive Plans - Restricted Stock Units (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>106</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R107.htm</HtmlFileName>
      <LongName>106 - Disclosure - Note 18 - Equity Incentive Plans - Tax Short-fall from Share-based Payment Arrangements (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-18-equity-incentive-plans-tax-shortfall-from-sharebased-payment-arrangements-details</Role>
      <ShortName>Note 18 - Equity Incentive Plans - Tax Short-fall from Share-based Payment Arrangements (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>107</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R108.htm</HtmlFileName>
      <LongName>107 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp-balance-sheets-details</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>108</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R109.htm</HtmlFileName>
      <LongName>108 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp-balance-sheets-details-parentheticals</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) (Parentheticals)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>109</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R110.htm</HtmlFileName>
      <LongName>109 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp - Statements of Operations (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp-statements-of-operations-details</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp - Statements of Operations (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>110</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R111.htm</HtmlFileName>
      <LongName>110 - Disclosure - Note 19 - Condensed Financial Information of Cathay General Bancorp - Statements of Cash Flows (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-19-condensed-financial-information-of-cathay-general-bancorp-statements-of-cash-flows-details</Role>
      <ShortName>Note 19 - Condensed Financial Information of Cathay General Bancorp - Statements of Cash Flows (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>111</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R112.htm</HtmlFileName>
      <LongName>111 - Disclosure - Note 20 - Dividend Reinvestment Plan (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-20-dividend-reinvestment-plan-details-textual</Role>
      <ShortName>Note 20 - Dividend Reinvestment Plan (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>112</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R113.htm</HtmlFileName>
      <LongName>112 - Disclosure - Note 21 - Regulatory Matters (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-21-regulatory-matters-details-textual</Role>
      <ShortName>Note 21 - Regulatory Matters (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>113</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R114.htm</HtmlFileName>
      <LongName>113 - Disclosure - Note 21 - Regulatory Matters - Capital and Leverage Ratios (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-21-regulatory-matters-capital-and-leverage-ratios-details</Role>
      <ShortName>Note 21 - Regulatory Matters - Capital and Leverage Ratios (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>114</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R115.htm</HtmlFileName>
      <LongName>114 - Disclosure - Note 22 - Balance Sheet Offsetting - Financial Instruments that are Eligible for Offset in the Consolidated Balance Sheet (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-22-balance-sheet-offsetting-financial-instruments-that-are-eligible-for-offset-in-the-consolidated-balance-sheet-details</Role>
      <ShortName>Note 22 - Balance Sheet Offsetting - Financial Instruments that are Eligible for Offset in the Consolidated Balance Sheet (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>115</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R116.htm</HtmlFileName>
      <LongName>115 - Disclosure - Note 23 - Quarterly Results of Operations (Unaudited) - Selected Unaudited Quarterly Financial Data (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-23-quarterly-results-of-operations-unaudited-selected-unaudited-quarterly-financial-data-details</Role>
      <ShortName>Note 23 - Quarterly Results of Operations (Unaudited) - Selected Unaudited Quarterly Financial Data (Details)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>116</Position>
    </Report>
    <Report instance="caty-20161231.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R117.htm</HtmlFileName>
      <LongName>116 - Disclosure - Note 24 - Subsequent Events (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cathaygeneralbancorp.com/20161231/role/statement-note-24-subsequent-events-details-textual</Role>
      <ShortName>Note 24 - Subsequent Events (Details Textual)</ShortName>
      <MenuCategory>Uncategorized</MenuCategory>
      <Position>117</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>caty-20161231.xml</File>
    <File>caty-20161231.xsd</File>
    <File>caty-20161231_cal.xml</File>
    <File>caty-20161231_def.xml</File>
    <File>caty-20161231_lab.xml</File>
    <File>caty-20161231_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies/>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
