<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.10.0.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>179</ContextCount>
  <ElementCount>256</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>65</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>5</UnitCount>
  <MyReports>
    <Report instance="cohu-20180929.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.cohu.com/20180929/role/statement-document-and-entity-information</Role>
      <ShortName>Document And Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>001 - Statement - Condensed Consolidated Balance Sheets (Current Period Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Current Period Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>002 - Statement - Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-condensed-consolidated-balance-sheets-current-period-unaudited-parentheticals</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>003 - Statement - Condensed Consolidated Statements of Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-condensed-consolidated-statements-of-income-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>004 - Statement - Condensed Consolidated Statements of Comprehensive Income (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-condensed-consolidated-statements-of-comprehensive-income-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>005 - Statement - Condensed Consolidated Statements of Cash Flows (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-condensed-consolidated-statements-of-cash-flows-unaudited</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>006 - Disclosure - Note 1 - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>007 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>008 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>009 - Disclosure - Note 4 - Employee Stock Benefit Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-4-employee-stock-benefit-plans</Role>
      <ShortName>Note 4 - Employee Stock Benefit Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>010 - Disclosure - Note 5 - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-5-income-taxes</Role>
      <ShortName>Note 5 - Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>011 - Disclosure - Note 6 - Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-6-contingencies</Role>
      <ShortName>Note 6 - Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>012 - Disclosure - Note 7 - Guarantees and Other Obligations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations</Role>
      <ShortName>Note 7 - Guarantees and Other Obligations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>013 - Disclosure - Note 8 - Acquisition of Xcerra</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-8-acquisition-of-xcerra</Role>
      <ShortName>Note 8 - Acquisition of Xcerra</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>014 - Disclosure - Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-significant-accounting-policies-policies</Role>
      <ShortName>Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies</ParentRole>
      <Position>15</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>015 - Disclosure - Note 1 - Summary of Significant Accounting Policies (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-tables</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies</ParentRole>
      <Position>16</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>016 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets-tables</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets</ParentRole>
      <Position>17</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>017 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-tables</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value</ParentRole>
      <Position>18</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>018 - Disclosure - Note 7 - Guarantees and Other Obligations (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations-tables</Role>
      <ShortName>Note 7 - Guarantees and Other Obligations (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations</ParentRole>
      <Position>19</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>019 - Disclosure - Note 1 - Summary of Significant Accounting Policies (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-details-textual</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-tables</ParentRole>
      <Position>20</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>020 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-inventories-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>021 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-property-plant-and-equipment-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Property, Plant and Equipment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>022 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Reported Share-based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-reported-sharebased-compensation-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Reported Share-based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>023 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Computation of Basic and Diluted Income (Loss) Per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-computation-of-basic-and-diluted-income-loss-per-share-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Computation of Basic and Diluted Income (Loss) Per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>024 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Cumulative-effect Adjustments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-cumulativeeffect-adjustments-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Cumulative-effect Adjustments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>025 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-disaggregation-of-revenue-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Disaggregation of Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>026 - Disclosure - Note 1 - Summary of Significant Accounting Policies - Customer Concentration (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-1-summary-of-significant-accounting-policies-customer-concentration-details</Role>
      <ShortName>Note 1 - Summary of Significant Accounting Policies - Customer Concentration (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>027 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets-details-textual</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets-tables</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>028 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets - Total Purchase Price (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets-total-purchase-price-details</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets - Total Purchase Price (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>29</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>029 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets - Fair Value of Contingent Consideration (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-purchased-intangible-assets-fair-value-of-contingent-consideration-details</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Purchased Intangible Assets - Fair Value of Contingent Consideration (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>30</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>030 - Disclosure - Note 2 - Business Acquisitions, Goodwill and Other Purchased Intangible Assets - Changes in Carrying Value of Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-goodwill-and-other-purchased-intangible-assets-changes-in-carrying-value-of-goodwill-details</Role>
      <ShortName>Note 2 - Business Acquisitions, Goodwill and Other Purchased Intangible Assets - Changes in Carrying Value of Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>31</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>031 - Disclosure - Note 2 - Business Acquisitions - Preliminary Allocation of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-2-business-acquisitions-preliminary-allocation-of-intangible-assets-details</Role>
      <ShortName>Note 2 - Business Acquisitions - Preliminary Allocation of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>32</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>032 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-details-textual</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-tables</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>033 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-shortterm-investments-by-security-type-details</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value - Short-term Investments by Security Type (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>34</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>034 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-effective-maturities-of-shortterm-investments-details</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value - Effective Maturities of Short-term Investments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>35</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>035 - Disclosure - Note 3 - Financial Instruments Measured at Fair Value - Assets Measured at Fair Value on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-3-financial-instruments-measured-at-fair-value-assets-measured-at-fair-value-on-recurring-basis-details</Role>
      <ShortName>Note 3 - Financial Instruments Measured at Fair Value - Assets Measured at Fair Value on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>036 - Disclosure - Note 4 - Employee Stock Benefit Plans (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-4-employee-stock-benefit-plans-details-textual</Role>
      <ShortName>Note 4 - Employee Stock Benefit Plans (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-4-employee-stock-benefit-plans</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>037 - Disclosure - Note 5 - Income Taxes (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-5-income-taxes-details-textual</Role>
      <ShortName>Note 5 - Income Taxes (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-5-income-taxes</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>038 - Disclosure - Note 7 - Guarantees and Other Obligations (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations-details-textual</Role>
      <ShortName>Note 7 - Guarantees and Other Obligations (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations-tables</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>039 - Disclosure - Note 7 - Guarantees and Other Obligations - Changes in Accrued Warranty (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-7-guarantees-and-other-obligations-changes-in-accrued-warranty-details</Role>
      <ShortName>Note 7 - Guarantees and Other Obligations - Changes in Accrued Warranty (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="cohu-20180929.xml">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>040 - Disclosure - Note 8 - Acquisition of Xcerra (Details Textual)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.cohu.com/20180929/role/statement-note-8-acquisition-of-xcerra-details-textual</Role>
      <ShortName>Note 8 - Acquisition of Xcerra (Details Textual)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.cohu.com/20180929/role/statement-note-8-acquisition-of-xcerra</ParentRole>
      <Position>41</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File>cohu-20180929.xml</File>
    <File>cohu-20180929.xsd</File>
    <File>cohu-20180929_cal.xml</File>
    <File>cohu-20180929_def.xml</File>
    <File>cohu-20180929_lab.xml</File>
    <File>cohu-20180929_pre.xml</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2018-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2017-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2018-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
