<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>441</ContextCount>
  <ElementCount>401</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>85</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001002 - Statement - Condensed Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CondensedConsolidatedBalanceSheets</Role>
      <ShortName>Condensed Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002003 - Statement - Condensed Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CondensedConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Condensed Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003004 - Statement - Condensed Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CondensedConsolidatedStatementsofIncome</Role>
      <ShortName>Condensed Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004005 - Statement - Condensed Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CondensedConsolidatedStatementsofComprehensiveIncome</Role>
      <ShortName>Condensed Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005006 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1006007 - Statement - Condensed Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CondensedConsolidatedStatementsofCashFlows</Role>
      <ShortName>Condensed Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Basis of Presentation and New Accounting Pronouncements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/BasisofPresentationandNewAccountingPronouncements</Role>
      <ShortName>Basis of Presentation and New Accounting Pronouncements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2105102 - Disclosure - Concentration of Credit and Other Risks</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/ConcentrationofCreditandOtherRisks</Role>
      <ShortName>Concentration of Credit and Other Risks</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2108103 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2111104 - Disclosure - Acquisition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Acquisition</Role>
      <ShortName>Acquisition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2116105 - Disclosure - Goodwill and Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/GoodwillandIntangibleAssets</Role>
      <ShortName>Goodwill and Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2121106 - Disclosure - Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Debt</Role>
      <ShortName>Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2128107 - Disclosure - Accrued Liabilities</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AccruedLiabilities</Role>
      <ShortName>Accrued Liabilities</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2131108 - Disclosure - Fair Value and Derivative Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstruments</Role>
      <ShortName>Fair Value and Derivative Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2140109 - Disclosure - Warranty</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Warranty</Role>
      <ShortName>Warranty</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2143110 - Disclosure - Property, Plant, and Equipment, net</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/PropertyPlantandEquipmentnet</Role>
      <ShortName>Property, Plant, and Equipment, net</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2146111 - Disclosure - Stockholders??? Equity and Stock-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensation</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2154112 - Disclosure - Net Income per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/NetIncomeperShare</Role>
      <ShortName>Net Income per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2157113 - Disclosure - Commitments and Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/CommitmentsandContingencies</Role>
      <ShortName>Commitments and Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2158114 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Leases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2163115 - Disclosure - Revenue</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/Revenue</Role>
      <ShortName>Revenue</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2165116 - Disclosure - Operating Segments and Enterprise-Wide Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformation</Role>
      <ShortName>Operating Segments and Enterprise-Wide Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2170117 - Disclosure - Subsequent Event (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.formfactor.com/role/SubsequentEventNotes</Role>
      <ShortName>Subsequent Event (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2202201 - Disclosure - Basis of Presentation and New Accounting Pronouncements (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/BasisofPresentationandNewAccountingPronouncementsPolicies</Role>
      <ShortName>Basis of Presentation and New Accounting Pronouncements (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/BasisofPresentationandNewAccountingPronouncements</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2306301 - Disclosure - Concentration of Credit and Other Risks (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/ConcentrationofCreditandOtherRisksTables</Role>
      <ShortName>Concentration of Credit and Other Risks (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/ConcentrationofCreditandOtherRisks</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2309302 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Inventories</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2312303 - Disclosure - Acquisition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AcquisitionTables</Role>
      <ShortName>Acquisition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Acquisition</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2317304 - Disclosure - Goodwill and Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/GoodwillandIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/GoodwillandIntangibleAssets</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2322305 - Disclosure - Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtTables</Role>
      <ShortName>Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Debt</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2329306 - Disclosure - Accrued Liabilities (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AccruedLiabilitiesTables</Role>
      <ShortName>Accrued Liabilities (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/AccruedLiabilities</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2332307 - Disclosure - Fair Value and Derivative Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsTables</Role>
      <ShortName>Fair Value and Derivative Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/FairValueandDerivativeInstruments</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2341308 - Disclosure - Warranty (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/WarrantyTables</Role>
      <ShortName>Warranty (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Warranty</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2344309 - Disclosure - Property, Plant, and Equipment, net (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/PropertyPlantandEquipmentnetTables</Role>
      <ShortName>Property, Plant, and Equipment, net (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/PropertyPlantandEquipmentnet</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2347310 - Disclosure - Stockholders??? Equity and Stock-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationTables</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensation</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2355311 - Disclosure - Net Income per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/NetIncomeperShareTables</Role>
      <ShortName>Net Income per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/NetIncomeperShare</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2359312 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/LeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Leases</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2366313 - Disclosure - Operating Segments and Enterprise-Wide Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformationTables</Role>
      <ShortName>Operating Segments and Enterprise-Wide Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformation</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2403401 - Disclosure - Basis of Presentation and New Accounting Pronouncements - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/BasisofPresentationandNewAccountingPronouncementsAdditionalInformationDetails</Role>
      <ShortName>Basis of Presentation and New Accounting Pronouncements - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2404402 - Disclosure - Basis of Presentation and New Accounting Pronouncements - ASU 2016-18 Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/BasisofPresentationandNewAccountingPronouncementsASU201618InformationDetails</Role>
      <ShortName>Basis of Presentation and New Accounting Pronouncements - ASU 2016-18 Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2407403 - Disclosure - Concentration of Credit and Other Risks (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/ConcentrationofCreditandOtherRisksDetails</Role>
      <ShortName>Concentration of Credit and Other Risks (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/ConcentrationofCreditandOtherRisksTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2410404 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/InventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/InventoriesTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2413405 - Disclosure - Acquisition - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AcquisitionAdditionalInformationDetails</Role>
      <ShortName>Acquisition - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2414406 - Disclosure - Acquisition - Assets Acquired and Liabilities Assumed (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AcquisitionAssetsAcquiredandLiabilitiesAssumedDetails</Role>
      <ShortName>Acquisition - Assets Acquired and Liabilities Assumed (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2415407 - Disclosure - Acquisition - Intangible Assets Acquired (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AcquisitionIntangibleAssetsAcquiredDetails</Role>
      <ShortName>Acquisition - Intangible Assets Acquired (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2418408 - Disclosure - Goodwill and Intangible Assets - Goodwill (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/GoodwillandIntangibleAssetsGoodwillDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Goodwill (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2419409 - Disclosure - Goodwill and Intangible Assets - Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/GoodwillandIntangibleAssetsIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2420410 - Disclosure - Goodwill and Intangible Assets - Amortization Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/GoodwillandIntangibleAssetsAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Intangible Assets - Amortization Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2423411 - Disclosure - Debt - Schedule of Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtScheduleofDebtDetails</Role>
      <ShortName>Debt - Schedule of Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2424412 - Disclosure - Debt - Maturity Schedule (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtMaturityScheduleDetails</Role>
      <ShortName>Debt - Maturity Schedule (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2425413 - Disclosure - Debt - CMI Term Loan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtCMITermLoanDetails</Role>
      <ShortName>Debt - CMI Term Loan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2426414 - Disclosure - Debt - FRT Term Loan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtFRTTermLoanDetails</Role>
      <ShortName>Debt - FRT Term Loan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2427415 - Disclosure - Debt - Building Term Loan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/DebtBuildingTermLoanDetails</Role>
      <ShortName>Debt - Building Term Loan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2430416 - Disclosure - Accrued Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/AccruedLiabilitiesDetails</Role>
      <ShortName>Accrued Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/AccruedLiabilitiesTables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2433417 - Disclosure - Fair Value and Derivative Instruments - Fair Value Assets Measured on Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsFairValueAssetsMeasuredonRecurringBasisDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Fair Value Assets Measured on Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2434418 - Disclosure - Fair Value and Derivative Instruments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsAdditionalInformationDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2435419 - Disclosure - Fair Value and Derivative Instruments - Impact of Cash Flow Hedges and Derivatives (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsImpactofCashFlowHedgesandDerivativesDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Impact of Cash Flow Hedges and Derivatives (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2436420 - Disclosure - Fair Value and Derivative Instruments - Foreign Currency Forward Contracts (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsForeignCurrencyForwardContractsDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Foreign Currency Forward Contracts (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2437421 - Disclosure - Fair Value and Derivative Instruments - Gains and Losses Related to Non-designated Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsGainsandLossesRelatedtoNondesignatedDerivativeInstrumentsDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Gains and Losses Related to Non-designated Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2438422 - Disclosure - Fair Value and Derivative Instruments - Assets Measured at Fair Value on a Non-Recurring Basis (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsAssetsMeasuredatFairValueonaNonRecurringBasisDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Assets Measured at Fair Value on a Non-Recurring Basis (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2439423 - Disclosure - Fair Value and Derivative Instruments - Impact of Foreign Exchange Derivattive Contracts Designated as Cash Flow Hedges (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/FairValueandDerivativeInstrumentsImpactofForeignExchangeDerivattiveContractsDesignatedasCashFlowHedgesDetails</Role>
      <ShortName>Fair Value and Derivative Instruments - Impact of Foreign Exchange Derivattive Contracts Designated as Cash Flow Hedges (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>2442424 - Disclosure - Warranty (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/WarrantyDetails</Role>
      <ShortName>Warranty (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/WarrantyTables</ParentRole>
      <Position>62</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>2445425 - Disclosure - Property, Plant, and Equipment, net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/PropertyPlantandEquipmentnetDetails</Role>
      <ShortName>Property, Plant, and Equipment, net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/PropertyPlantandEquipmentnetTables</ParentRole>
      <Position>63</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>2448426 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>2449427 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - Restricted Stock Unit Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationRestrictedStockUnitActivityDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - Restricted Stock Unit Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>2450428 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - Stock Option Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationStockOptionActivityDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - Stock Option Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>2451429 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - ESPP Activity (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationESPPActivityDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - ESPP Activity (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>2452430 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - Stock-Based Compensation (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationStockBasedCompensationDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - Stock-Based Compensation (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>2453431 - Disclosure - Stockholders??? Equity and Stock-Based Compensation - Unrecognized Compensation Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/StockholdersEquityandStockBasedCompensationUnrecognizedCompensationCostsDetails</Role>
      <ShortName>Stockholders??? Equity and Stock-Based Compensation - Unrecognized Compensation Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>2456432 - Disclosure - Net Income per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/NetIncomeperShareDetails</Role>
      <ShortName>Net Income per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/NetIncomeperShareTables</ParentRole>
      <Position>70</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>2460433 - Disclosure - Leases - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/LeasesNarrativeDetails</Role>
      <ShortName>Leases - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>2461434 - Disclosure - Leases - Components of Lease Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/LeasesComponentsofLeaseExpenseDetails</Role>
      <ShortName>Leases - Components of Lease Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R73.htm</HtmlFileName>
      <LongName>2462435 - Disclosure - Leases - Schedule of Future Minimum Payments Under Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/LeasesScheduleofFutureMinimumPaymentsUnderLeasesDetails</Role>
      <ShortName>Leases - Schedule of Future Minimum Payments Under Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>73</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R74.htm</HtmlFileName>
      <LongName>2464436 - Disclosure - Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/RevenueDetails</Role>
      <ShortName>Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/Revenue</ParentRole>
      <Position>74</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R75.htm</HtmlFileName>
      <LongName>2467437 - Disclosure - Operating Segments and Enterprise-Wide Information - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformationAdditionalInformationDetails</Role>
      <ShortName>Operating Segments and Enterprise-Wide Information - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>75</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R76.htm</HtmlFileName>
      <LongName>2468438 - Disclosure - Operating Segments and Enterprise-Wide Information - Operating Results by Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformationOperatingResultsbySegmentDetails</Role>
      <ShortName>Operating Segments and Enterprise-Wide Information - Operating Results by Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>76</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R77.htm</HtmlFileName>
      <LongName>2469439 - Disclosure - Operating Segments and Enterprise-Wide Information - Revenue by Segment, Recognition Type, and Geographic Area (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/OperatingSegmentsandEnterpriseWideInformationRevenuebySegmentRecognitionTypeandGeographicAreaDetails</Role>
      <ShortName>Operating Segments and Enterprise-Wide Information - Revenue by Segment, Recognition Type, and Geographic Area (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>77</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R78.htm</HtmlFileName>
      <LongName>2471440 - Disclosure - Subsequent Event (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.formfactor.com/role/SubsequentEventDetails</Role>
      <ShortName>Subsequent Event (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.formfactor.com/role/SubsequentEventNotes</ParentRole>
      <Position>78</Position>
    </Report>
    <Report instance="form-20200627.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9999.htm</HtmlFileName>
      <LongName>Uncategorized Items - form-20200627.htm</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/role/uncategorizedFacts</Role>
      <ShortName>Uncategorized Items - form-20200627.htm</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>79</Position>
    </Report>
    <Report>
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <LongName>All Reports</LongName>
      <ReportType>Book</ReportType>
      <ShortName>All Reports</ShortName>
    </Report>
  </MyReports>
  <InputFiles>
    <File doctype="10-Q" original="form-20200627.htm">form-20200627.htm</File>
    <File>form-20200627.xsd</File>
    <File>form-20200627_cal.xml</File>
    <File>form-20200627_def.xml</File>
    <File>form-20200627_lab.xml</File>
    <File>form-20200627_pre.xml</File>
    <File>formq220exh3101.htm</File>
    <File>formq220exh3102.htm</File>
    <File>formq220exh3201.htm</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/currency/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/country/2020-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
