<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.20.2</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>247</ContextCount>
  <ElementCount>292</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>56</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>7</UnitCount>
  <MyReports>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>0001001 - Document - Cover Page</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/CoverPage</Role>
      <ShortName>Cover Page</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>1001002 - Statement - Consolidated Statements of Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedStatementsofIncome</Role>
      <ShortName>Consolidated Statements of Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>1002003 - Statement - Consolidated Statements of Comprehensive Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedStatementsofComprehensiveIncome</Role>
      <ShortName>Consolidated Statements of Comprehensive Income</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>1003004 - Statement - Consolidated Balance Sheets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedBalanceSheets</Role>
      <ShortName>Consolidated Balance Sheets</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>1004005 - Statement - Consolidated Balance Sheets (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedBalanceSheetsParenthetical</Role>
      <ShortName>Consolidated Balance Sheets (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>1005006 - Statement - Consolidated Statements of Cash Flows</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedStatementsofCashFlows</Role>
      <ShortName>Consolidated Statements of Cash Flows</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>1006007 - Statement - Consolidated Statement of Shareholders' Equity</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedStatementofShareholdersEquity</Role>
      <ShortName>Consolidated Statement of Shareholders' Equity</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>1007008 - Statement - Consolidated Statement of Shareholders' Equity (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedStatementofShareholdersEquityParenthetical</Role>
      <ShortName>Consolidated Statement of Shareholders' Equity (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>2101101 - Disclosure - Consolidated Financial Statements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ConsolidatedFinancialStatements</Role>
      <ShortName>Consolidated Financial Statements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>2102102 - Disclosure - Recent Accounting Pronouncements (Notes)</LongName>
      <ReportType>Notes</ReportType>
      <Role>http://www.gibraltar1.com/role/RecentAccountingPronouncementsNotes</Role>
      <ShortName>Recent Accounting Pronouncements (Notes)</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>2106103 - Disclosure - Accounts Receivable and Allowance for Doubtful Accounts</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccountsReceivableandAllowanceforDoubtfulAccounts</Role>
      <ShortName>Accounts Receivable and Allowance for Doubtful Accounts</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>2110104 - Disclosure - Revenue Revenue</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RevenueRevenue</Role>
      <ShortName>Revenue Revenue</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>2114105 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/Inventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>2117106 - Disclosure - Acquisitions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/Acquisitions</Role>
      <ShortName>Acquisitions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>2123107 - Disclosure - Goodwill and Related Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssets</Role>
      <ShortName>Goodwill and Related Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>2128108 - Disclosure - Long-Term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/LongTermDebt</Role>
      <ShortName>Long-Term Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>2130109 - Disclosure - Accumulated Other Comprehensive (Loss) Income</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccumulatedOtherComprehensiveLossIncome</Role>
      <ShortName>Accumulated Other Comprehensive (Loss) Income</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>2133110 - Disclosure - Equity-Based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EquityBasedCompensation</Role>
      <ShortName>Equity-Based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>2138111 - Disclosure - Exit Activity Costs and Asset Impairments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairments</Role>
      <ShortName>Exit Activity Costs and Asset Impairments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>2144112 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/IncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>2147113 - Disclosure - Earnings per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EarningsperShare</Role>
      <ShortName>Earnings per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>2150114 - Disclosure - Segment Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/SegmentInformation</Role>
      <ShortName>Segment Information</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>2203201 - Disclosure - Recent Accounting Pronouncements (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RecentAccountingPronouncementsPolicies</Role>
      <ShortName>Recent Accounting Pronouncements (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/RecentAccountingPronouncementsNotes</ParentRole>
      <Position>23</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>2304301 - Disclosure - Recent Accounting Pronouncements - (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RecentAccountingPronouncementsTables</Role>
      <ShortName>Recent Accounting Pronouncements - (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/RecentAccountingPronouncementsNotes</ParentRole>
      <Position>24</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>2307302 - Disclosure - Accounts Receivable and Allowance for Doubtful Accounts (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccountsReceivableandAllowanceforDoubtfulAccountsTables</Role>
      <ShortName>Accounts Receivable and Allowance for Doubtful Accounts (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AccountsReceivableandAllowanceforDoubtfulAccounts</ParentRole>
      <Position>25</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>2311303 - Disclosure - Revenue (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RevenueTables</Role>
      <ShortName>Revenue (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/RevenueRevenue</ParentRole>
      <Position>26</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>2315304 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/InventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/Inventories</ParentRole>
      <Position>27</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>2318305 - Disclosure - Acquisitions (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AcquisitionsTables</Role>
      <ShortName>Acquisitions (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/Acquisitions</ParentRole>
      <Position>28</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>2324306 - Disclosure - Goodwill and Related Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Related Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssets</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>2331307 - Disclosure - Accumulated Other Comprehensive (Loss) Income (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccumulatedOtherComprehensiveLossIncomeTables</Role>
      <ShortName>Accumulated Other Comprehensive (Loss) Income (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AccumulatedOtherComprehensiveLossIncome</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>2334308 - Disclosure - Equity-Based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EquityBasedCompensationTables</Role>
      <ShortName>Equity-Based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/EquityBasedCompensation</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>2339309 - Disclosure - Exit Activity Costs and Asset Impairments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsTables</Role>
      <ShortName>Exit Activity Costs and Asset Impairments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairments</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>2345310 - Disclosure - Income Taxes (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/IncomeTaxesTables</Role>
      <ShortName>Income Taxes (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/IncomeTaxes</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>2348311 - Disclosure - Earnings per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EarningsperShareTables</Role>
      <ShortName>Earnings per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/EarningsperShare</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>2351312 - Disclosure - Segment Information (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/SegmentInformationTables</Role>
      <ShortName>Segment Information (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/SegmentInformation</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>2405401 - Disclosure - Recent Accounting Pronouncements - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RecentAccountingPronouncementsNarrativeDetails</Role>
      <ShortName>Recent Accounting Pronouncements - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>36</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>2408402 - Disclosure - Accounts Receivable and Allowance for Doubtful Accounts - Schedule of Receivables (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccountsReceivableandAllowanceforDoubtfulAccountsScheduleofReceivablesDetails</Role>
      <ShortName>Accounts Receivable and Allowance for Doubtful Accounts - Schedule of Receivables (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>37</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>2409403 - Disclosure - Accounts Receivable and Allowance for Doubtful Accounts - Schedule of Accounts Receivable Allowance for Credit Losses (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccountsReceivableandAllowanceforDoubtfulAccountsScheduleofAccountsReceivableAllowanceforCreditLossesDetails</Role>
      <ShortName>Accounts Receivable and Allowance for Doubtful Accounts - Schedule of Accounts Receivable Allowance for Credit Losses (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>38</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>2412404 - Disclosure - Revenue - Narrative (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RevenueNarrativeDetails</Role>
      <ShortName>Revenue - Narrative (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>39</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>2413405 - Disclosure - Revenue - Contract Assets and Liabilities (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/RevenueContractAssetsandLiabilitiesDetails</Role>
      <ShortName>Revenue - Contract Assets and Liabilities (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>2416406 - Disclosure - Inventories (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/InventoriesDetails</Role>
      <ShortName>Inventories (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/InventoriesTables</ParentRole>
      <Position>41</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>2419407 - Disclosure - Acquisitions (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AcquisitionsNarrativeDetails</Role>
      <ShortName>Acquisitions (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AcquisitionsTables</ParentRole>
      <Position>42</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>2420408 - Disclosure - Acquisitions (Allocation of Purchase Consideration to the Assets Acquired and Liabilities Assumed) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AcquisitionsAllocationofPurchaseConsiderationtotheAssetsAcquiredandLiabilitiesAssumedDetails</Role>
      <ShortName>Acquisitions (Allocation of Purchase Consideration to the Assets Acquired and Liabilities Assumed) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AcquisitionsTables</ParentRole>
      <Position>43</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>2421409 - Disclosure - Acquisitions (Schedule of Acquired Intangible Assets) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AcquisitionsScheduleofAcquiredIntangibleAssetsDetails</Role>
      <ShortName>Acquisitions (Schedule of Acquired Intangible Assets) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AcquisitionsTables</ParentRole>
      <Position>44</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>2422410 - Disclosure - Acquisitions - Acquisition Related Costs (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AcquisitionsAcquisitionRelatedCostsDetails</Role>
      <ShortName>Acquisitions - Acquisition Related Costs (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>2425411 - Disclosure - Goodwill and Related Intangible Assets (Schedule of Changes in Carrying Amount of Goodwill) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsScheduleofChangesinCarryingAmountofGoodwillDetails</Role>
      <ShortName>Goodwill and Related Intangible Assets (Schedule of Changes in Carrying Amount of Goodwill) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsTables</ParentRole>
      <Position>46</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>2426412 - Disclosure - Goodwill and Related Intangible Assets (Schedule of Acquired Intangible Assets) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsScheduleofAcquiredIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Related Intangible Assets (Schedule of Acquired Intangible Assets) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsTables</ParentRole>
      <Position>47</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>2427413 - Disclosure - Goodwill and Related Intangible Assets (Schedule of Amortization Expense) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsScheduleofAmortizationExpenseDetails</Role>
      <ShortName>Goodwill and Related Intangible Assets (Schedule of Amortization Expense) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/GoodwillandRelatedIntangibleAssetsTables</ParentRole>
      <Position>48</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>2429414 - Disclosure - Long-Term Debt (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/LongTermDebtNarrativeDetails</Role>
      <ShortName>Long-Term Debt (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/LongTermDebt</ParentRole>
      <Position>49</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>2432415 - Disclosure - Accumulated Other Comprehensive (Loss) Income (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/AccumulatedOtherComprehensiveLossIncomeDetails</Role>
      <ShortName>Accumulated Other Comprehensive (Loss) Income (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/AccumulatedOtherComprehensiveLossIncomeTables</ParentRole>
      <Position>50</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>2435416 - Disclosure - Equity-Based Compensation - Incentive Plan (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EquityBasedCompensationIncentivePlanDetails</Role>
      <ShortName>Equity-Based Compensation - Incentive Plan (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>2436417 - Disclosure - Equity-Based Compensation (Schedule of Number of Awards and Weighted Average Grant Date Fair Value) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EquityBasedCompensationScheduleofNumberofAwardsandWeightedAverageGrantDateFairValueDetails</Role>
      <ShortName>Equity-Based Compensation (Schedule of Number of Awards and Weighted Average Grant Date Fair Value) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/EquityBasedCompensationTables</ParentRole>
      <Position>52</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>2437418 - Disclosure - Equity-Based Compensation (Equity Based Awards - Settled in Cash) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EquityBasedCompensationEquityBasedAwardsSettledinCashDetails</Role>
      <ShortName>Equity-Based Compensation (Equity Based Awards - Settled in Cash) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/EquityBasedCompensationTables</ParentRole>
      <Position>53</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>2440419 - Disclosure - Exit Activity Costs and Asset Impairments (Narrative) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsNarrativeDetails</Role>
      <ShortName>Exit Activity Costs and Asset Impairments (Narrative) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsTables</ParentRole>
      <Position>54</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>2441420 - Disclosure - Exit Activity Costs and Asset Impairments (Summary of Exit Activity Costs and Asset Impairments by Segment) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsSummaryofExitActivityCostsandAssetImpairmentsbySegmentDetails</Role>
      <ShortName>Exit Activity Costs and Asset Impairments (Summary of Exit Activity Costs and Asset Impairments by Segment) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsTables</ParentRole>
      <Position>55</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>2442421 - Disclosure - Exit Activity Costs and Asset Impairments (Summary of Exit Activity Costs and Asset Impairments) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsSummaryofExitActivityCostsandAssetImpairmentsDetails</Role>
      <ShortName>Exit Activity Costs and Asset Impairments (Summary of Exit Activity Costs and Asset Impairments) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsTables</ParentRole>
      <Position>56</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>2443422 - Disclosure - Exit Activity Costs and Asset Impairments (Reconciles of Liability for Exit Activity Costs Relating to Facility Consolidation Efforts) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsReconcilesofLiabilityforExitActivityCostsRelatingtoFacilityConsolidationEffortsDetails</Role>
      <ShortName>Exit Activity Costs and Asset Impairments (Reconciles of Liability for Exit Activity Costs Relating to Facility Consolidation Efforts) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/ExitActivityCostsandAssetImpairmentsTables</ParentRole>
      <Position>57</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>2446423 - Disclosure - Income Taxes (Provision For Income Taxes For Continuing Operations) (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/IncomeTaxesProvisionForIncomeTaxesForContinuingOperationsDetails</Role>
      <ShortName>Income Taxes (Provision For Income Taxes For Continuing Operations) (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/IncomeTaxesTables</ParentRole>
      <Position>58</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>2449424 - Disclosure - Earnings per Share (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/EarningsperShareDetails</Role>
      <ShortName>Earnings per Share (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/EarningsperShareTables</ParentRole>
      <Position>59</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>2452425 - Disclosure - Segment Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/SegmentInformationDetails</Role>
      <ShortName>Segment Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <ParentRole>http://www.gibraltar1.com/role/SegmentInformationTables</ParentRole>
      <Position>60</Position>
    </Report>
    <Report instance="rock-20200630.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>2453426 - Disclosure - Segment Information - Disaggregation of Revenue (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.gibraltar1.com/role/SegmentInformationDisaggregationofRevenueDetails</Role>
      <ShortName>Segment Information - Disaggregation of Revenue (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</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="rock-20200630.htm">rock-20200630.htm</File>
    <File>q22020exhibit311.htm</File>
    <File>q22020exhibit312.htm</File>
    <File>q22020exhibit321.htm</File>
    <File>q22020exhibit322.htm</File>
    <File>rock-20200630.xsd</File>
    <File>rock-20200630_cal.xml</File>
    <File>rock-20200630_def.xml</File>
    <File>rock-20200630_lab.xml</File>
    <File>rock-20200630_pre.xml</File>
  </InputFiles>
  <SupplementalFiles>
    <File>rock-20200630_g1.gif</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy>http://fasb.org/us-gaap/2020-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://xbrl.sec.gov/dei/2019-01-31</BaseTaxonomy>
    <BaseTaxonomy>http://fasb.org/srt/2020-01-31</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>true</HasPresentationLinkbase>
  <HasCalculationLinkbase>true</HasCalculationLinkbase>
</FilingSummary>
