<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.25.3</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>413</ContextCount>
  <ElementCount>334</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>true</FootnotesReported>
  <SegmentCount>86</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>6</UnitCount>
  <MyReports>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>75000 - Document - Document and Entity Information</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DocumentDocumentAndEntityInformation</Role>
      <ShortName>Document and Entity Information</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.htm</HtmlFileName>
      <LongName>75010 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>2</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>75020 - Statement - CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedBalanceSheetsUnauditedParenthetical</Role>
      <ShortName>CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>3</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R4.htm</HtmlFileName>
      <LongName>75030 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedStatementsOfOperationsUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>4</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R5.htm</HtmlFileName>
      <LongName>75040 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedStatementsOfComprehensiveLossUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>5</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R6.htm</HtmlFileName>
      <LongName>75050 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedStatementsOfComprehensiveLossParentheticalUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF COMPREHENSIVE LOSS (Parenthetical) (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>6</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R7.htm</HtmlFileName>
      <LongName>75060 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS 'EQUITY (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedStatementsOfStockholdersEquityUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS 'EQUITY (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>7</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R8.htm</HtmlFileName>
      <LongName>75070 - Statement - CONDENS ED CONSOLIDATED STATEMENTS OF STOCKHOLDERS ' EQUITY (Unaudited) (Parenthetical)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensEdConsolidatedStatementsOfStockholdersEquityUnauditedParenthetical</Role>
      <ShortName>CONDENS ED CONSOLIDATED STATEMENTS OF STOCKHOLDERS ' EQUITY (Unaudited) (Parenthetical)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>8</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R9.htm</HtmlFileName>
      <LongName>75080 - Statement - CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/StatementCondensedConsolidatedStatementsOfCashFlowsUnaudited</Role>
      <ShortName>CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (Unaudited)</ShortName>
      <MenuCategory>Statements</MenuCategory>
      <Position>9</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R10.htm</HtmlFileName>
      <LongName>995410 - Disclosure - Pay vs Performance Disclosure</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/PvpDisclosure</Role>
      <ShortName>Pay vs Performance Disclosure</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>10</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R11.htm</HtmlFileName>
      <LongName>995445 - Disclosure - Insider Trading Arrangements</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingArrangements</Role>
      <ShortName>Insider Trading Arrangements</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>11</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R12.htm</HtmlFileName>
      <LongName>995455 - Disclosure - Organization and Nature of Operations</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureOrganizationAndNatureOfOperations</Role>
      <ShortName>Organization and Nature of Operations</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>12</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R13.htm</HtmlFileName>
      <LongName>995465 - Disclosure - Summary of Significant Accounting Policies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>13</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R14.htm</HtmlFileName>
      <LongName>995475 - Disclosure - Revenue Recognition</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRevenueRecognition</Role>
      <ShortName>Revenue Recognition</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>14</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R15.htm</HtmlFileName>
      <LongName>995485 - Disclosure - Related Party Transactions</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRelatedPartyTransactions</Role>
      <ShortName>Related Party Transactions</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>15</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R16.htm</HtmlFileName>
      <LongName>995495 - Disclosure - Inventories</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureInventories</Role>
      <ShortName>Inventories</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>16</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R17.htm</HtmlFileName>
      <LongName>995505 - Disclosure - Property and Equipment and Rental Fleet</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleet</Role>
      <ShortName>Property and Equipment and Rental Fleet</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>17</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R18.htm</HtmlFileName>
      <LongName>995515 - Disclosure - Goodwill and Other Intangible Assets</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssets</Role>
      <ShortName>Goodwill and Other Intangible Assets</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>18</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R19.htm</HtmlFileName>
      <LongName>995535 - Disclosure - Floor Plans</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFloorPlans</Role>
      <ShortName>Floor Plans</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>19</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R20.htm</HtmlFileName>
      <LongName>995545 - Disclosure - Long-term Debt</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureLongTermDebt</Role>
      <ShortName>Long-term Debt</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>20</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R21.htm</HtmlFileName>
      <LongName>995565 - Disclosure - Leases</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeases</Role>
      <ShortName>Leases</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>21</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R22.htm</HtmlFileName>
      <LongName>995575 - Disclosure - Contingencies</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureContingencies</Role>
      <ShortName>Contingencies</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>22</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R23.htm</HtmlFileName>
      <LongName>995585 - Disclosure - Income Taxes</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureIncomeTaxes</Role>
      <ShortName>Income Taxes</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>23</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R24.htm</HtmlFileName>
      <LongName>995595 - Disclosure - Stock-based Compensation</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureStockbasedCompensation</Role>
      <ShortName>Stock-based Compensation</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>24</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R25.htm</HtmlFileName>
      <LongName>995605 - Disclosure - Fair Value of Financial Instruments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstruments</Role>
      <ShortName>Fair Value of Financial Instruments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>25</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R26.htm</HtmlFileName>
      <LongName>995615 - Disclosure - Business Combinations and Divestitures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureBusinessCombinationsAndDivestitures</Role>
      <ShortName>Business Combinations and Divestitures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>26</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R27.htm</HtmlFileName>
      <LongName>995625 - Disclosure - Segments</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSegments</Role>
      <ShortName>Segments</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>27</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R28.htm</HtmlFileName>
      <LongName>995635 - Disclosure - Earnings Per Share</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureEarningsPerShare</Role>
      <ShortName>Earnings Per Share</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>28</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R29.htm</HtmlFileName>
      <LongName>995655 - Disclosure - Summary of Significant Accounting Policies (Policies)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPoliciesPolicies</Role>
      <ShortName>Summary of Significant Accounting Policies (Policies)</ShortName>
      <MenuCategory>Policies</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSummaryOfSignificantAccountingPolicies</ParentRole>
      <Position>29</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R30.htm</HtmlFileName>
      <LongName>995675 - Disclosure - Revenue Recognition (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRevenueRecognitionTables</Role>
      <ShortName>Revenue Recognition (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRevenueRecognition</ParentRole>
      <Position>30</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R31.htm</HtmlFileName>
      <LongName>995685 - Disclosure - Inventories (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureInventoriesTables</Role>
      <ShortName>Inventories (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureInventories</ParentRole>
      <Position>31</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R32.htm</HtmlFileName>
      <LongName>995695 - Disclosure - Property and Equipment and Rental Fleet (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleetTables</Role>
      <ShortName>Property and Equipment and Rental Fleet (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleet</ParentRole>
      <Position>32</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R33.htm</HtmlFileName>
      <LongName>995705 - Disclosure - Goodwill and Other Intangible Assets (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssetsTables</Role>
      <ShortName>Goodwill and Other Intangible Assets (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssets</ParentRole>
      <Position>33</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R34.htm</HtmlFileName>
      <LongName>995715 - Disclosure - Long-term Debt (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureLongTermDebtTables</Role>
      <ShortName>Long-term Debt (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureLongTermDebt</ParentRole>
      <Position>34</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R35.htm</HtmlFileName>
      <LongName>995735 - Disclosure - Leases (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeasesTables</Role>
      <ShortName>Leases (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeases</ParentRole>
      <Position>35</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R36.htm</HtmlFileName>
      <LongName>995745 - Disclosure - Stock-based Compensation (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureStockbasedCompensationTables</Role>
      <ShortName>Stock-based Compensation (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureStockbasedCompensation</ParentRole>
      <Position>36</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R37.htm</HtmlFileName>
      <LongName>995755 - Disclosure - Fair Value of Financial Instruments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsTables</Role>
      <ShortName>Fair Value of Financial Instruments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstruments</ParentRole>
      <Position>37</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R38.htm</HtmlFileName>
      <LongName>995775 - Disclosure - Segments (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSegmentsTables</Role>
      <ShortName>Segments (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSegments</ParentRole>
      <Position>38</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R39.htm</HtmlFileName>
      <LongName>995785 - Disclosure - Earnings Per Share (Tables)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureEarningsPerShareTables</Role>
      <ShortName>Earnings Per Share (Tables)</ShortName>
      <MenuCategory>Tables</MenuCategory>
      <ParentRole>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureEarningsPerShare</ParentRole>
      <Position>39</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R40.htm</HtmlFileName>
      <LongName>995815 - Disclosure - Revenue Recognition - Summary of Disaggregated Revenues (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRevenueRecognitionSummaryOfDisaggregatedRevenuesDetails</Role>
      <ShortName>Revenue Recognition - Summary of Disaggregated Revenues (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>40</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R41.htm</HtmlFileName>
      <LongName>995825 - Disclosure - Revenue Recognition - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRevenueRecognitionAdditionalInformationDetails</Role>
      <ShortName>Revenue Recognition - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>41</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R42.htm</HtmlFileName>
      <LongName>995835 - Disclosure - Related Party Transactions - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureRelatedPartyTransactionsAdditionalInformationDetails</Role>
      <ShortName>Related Party Transactions - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>42</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R43.htm</HtmlFileName>
      <LongName>995845 - Disclosure - Inventories - Summary of Inventories, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureInventoriesSummaryOfInventoriesNetDetails</Role>
      <ShortName>Inventories - Summary of Inventories, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>43</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R44.htm</HtmlFileName>
      <LongName>995855 - Disclosure - Inventories - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureInventoriesAdditionalInformationDetails</Role>
      <ShortName>Inventories - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>44</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R45.htm</HtmlFileName>
      <LongName>995865 - Disclosure - Property and Equipment and Rental Fleet - Schedule of Property and Equipment, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleetScheduleOfPropertyAndEquipmentNetDetails</Role>
      <ShortName>Property and Equipment and Rental Fleet - Schedule of Property and Equipment, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>45</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R46.htm</HtmlFileName>
      <LongName>995875 - Disclosure - Property and Equipment and Rental Fleet - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleetAdditionalInformationDetails</Role>
      <ShortName>Property and Equipment and Rental Fleet - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>46</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R47.htm</HtmlFileName>
      <LongName>995885 - Disclosure - Property and Equipment and Rental Fleet - Schedule of Rental Fleet, Net (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosurePropertyAndEquipmentAndRentalFleetScheduleOfRentalFleetNetDetails</Role>
      <ShortName>Property and Equipment and Rental Fleet - Schedule of Rental Fleet, Net (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>47</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R48.htm</HtmlFileName>
      <LongName>995895 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill in Total and by Reportable Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssetsScheduleOfChangesInCarryingAmountOfGoodwillInTotalAndByReportableSegmentDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Changes in Carrying Amount of Goodwill in Total and by Reportable Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>48</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R49.htm</HtmlFileName>
      <LongName>995905 - Disclosure - Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amount and Accumulated Amortization of Intangible Assets (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssetsScheduleOfGrossCarryingAmountAndAccumulatedAmortizationOfIntangibleAssetsDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Schedule of Gross Carrying Amount and Accumulated Amortization of Intangible Assets (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>49</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R50.htm</HtmlFileName>
      <LongName>995915 - Disclosure - Goodwill and Other Intangible Assets - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureGoodwillAndOtherIntangibleAssetsAdditionalInformationDetails</Role>
      <ShortName>Goodwill and Other Intangible Assets - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>50</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R51.htm</HtmlFileName>
      <LongName>995925 - Disclosure - Floor Plans - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFloorPlansAdditionalInformationDetails</Role>
      <ShortName>Floor Plans - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>51</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R52.htm</HtmlFileName>
      <LongName>995935 - Disclosure - Long-term Debt - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureLongTermDebtAdditionalInformationDetails</Role>
      <ShortName>Long-term Debt - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>52</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R53.htm</HtmlFileName>
      <LongName>995945 - Disclosure - Long-term Debt - Schedule of Long-term Debt (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureLongTermDebtScheduleOfLongTermDebtDetails</Role>
      <ShortName>Long-term Debt - Schedule of Long-term Debt (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>53</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R54.htm</HtmlFileName>
      <LongName>995965 - Disclosure - Long-term Debt - Schedule of Present Value of Cash Payments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLongtermDebtScheduleOfPresentValueOfCashPaymentsDetails</Role>
      <ShortName>Long-term Debt - Schedule of Present Value of Cash Payments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>54</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R55.htm</HtmlFileName>
      <LongName>995975 - Disclosure - Equity - Summary of Components of AOCI as Reported in Condensed Consolidated Balance Sheets, and Changes in AOCI by Components, Net of Tax (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureEquitySummaryOfComponentsOfAociAsReportedInCondensedConsolidatedBalanceSheetsAndChangesInAociByComponentsNetOfTaxDetails</Role>
      <ShortName>Equity - Summary of Components of AOCI as Reported in Condensed Consolidated Balance Sheets, and Changes in AOCI by Components, Net of Tax (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>55</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R56.htm</HtmlFileName>
      <LongName>995985 - Disclosure - Leases - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeasesAdditionalInformationDetails</Role>
      <ShortName>Leases - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>56</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R57.htm</HtmlFileName>
      <LongName>995995 - Disclosure - Leases - Components of Lease Expense (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeasesComponentsOfLeaseExpenseDetails</Role>
      <ShortName>Leases - Components of Lease Expense (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>57</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R58.htm</HtmlFileName>
      <LongName>996005 - Disclosure - Leases - Schedule of Additional Information Related to Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeasesScheduleOfAdditionalInformationRelatedToLeasesDetails</Role>
      <ShortName>Leases - Schedule of Additional Information Related to Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>58</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R59.htm</HtmlFileName>
      <LongName>996015 - Disclosure - Leases - Schedule of Minimum Future Lease Payments under Non-cancellable Operating and Finance Leases (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureLeasesScheduleOfMinimumFutureLeasePaymentsUnderNoncancellableOperatingAndFinanceLeasesDetails</Role>
      <ShortName>Leases - Schedule of Minimum Future Lease Payments under Non-cancellable Operating and Finance Leases (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>59</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R60.htm</HtmlFileName>
      <LongName>996035 - Disclosure - Contingencies - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureContingenciesAdditionalInformationDetails</Role>
      <ShortName>Contingencies - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>60</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R61.htm</HtmlFileName>
      <LongName>996045 - Disclosure - Income Taxes - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureIncomeTaxesAdditionalInformationDetails</Role>
      <ShortName>Income Taxes - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>61</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R62.htm</HtmlFileName>
      <LongName>996055 - Disclosure - Stock-based Compensation - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureStockbasedCompensationAdditionalInformationDetails</Role>
      <ShortName>Stock-based Compensation - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>62</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R63.htm</HtmlFileName>
      <LongName>996065 - Disclosure - Stock-based Compensation - Summary of Restricted And Performance Stock Granted, Vested and Issued (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureStockbasedCompensationSummaryOfRestrictedAndPerformanceStockGrantedVestedAndIssuedDetails</Role>
      <ShortName>Stock-based Compensation - Summary of Restricted And Performance Stock Granted, Vested and Issued (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>63</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R64.htm</HtmlFileName>
      <LongName>996075 - Disclosure - Fair Value of Financial Instruments - Summary of Fair Value and Carrying Value of Debt Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsSummaryOfFairValueAndCarryingValueOfDebtInstrumentsDetails</Role>
      <ShortName>Fair Value of Financial Instruments - Summary of Fair Value and Carrying Value of Debt Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>64</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R65.htm</HtmlFileName>
      <LongName>996085 - Disclosure - Fair Value of Financial Instruments - Schedule of Contingent Consideration Liabilities Measured and Recorded at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsScheduleOfContingentConsiderationLiabilitiesMeasuredAndRecordedAtFairValueDetails</Role>
      <ShortName>Fair Value of Financial Instruments - Schedule of Contingent Consideration Liabilities Measured and Recorded at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>65</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R66.htm</HtmlFileName>
      <LongName>996095 - Disclosure - Fair Value of Financial Instruments - Summary of Maturity Dates Unit of Measure and Notional Value for Derivative Instruments (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsSummaryOfMaturityDatesUnitOfMeasureAndNotionalValueForDerivativeInstrumentsDetails</Role>
      <ShortName>Fair Value of Financial Instruments - Summary of Maturity Dates Unit of Measure and Notional Value for Derivative Instruments (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>66</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R67.htm</HtmlFileName>
      <LongName>996105 - Disclosure - Fair Value of Financial Instruments - Summary of Derivative Instruments Measured at Fair Value (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureFairValueOfFinancialInstrumentsSummaryOfDerivativeInstrumentsMeasuredAtFairValueDetails</Role>
      <ShortName>Fair Value of Financial Instruments - Summary of Derivative Instruments Measured at Fair Value (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>67</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R68.htm</HtmlFileName>
      <LongName>996115 - Disclosure - Business Combinations and Divestitures - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureBusinessCombinationsAndDivestituresAdditionalInformationDetails</Role>
      <ShortName>Business Combinations and Divestitures - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>68</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R69.htm</HtmlFileName>
      <LongName>996135 - Disclosure - Segments - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSegmentsAdditionalInformationDetails</Role>
      <ShortName>Segments - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>69</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R70.htm</HtmlFileName>
      <LongName>996145 - Disclosure - Segments - Schedule of Results of Operations by Reportable Segment (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/Role_DisclosureSegmentsScheduleOfResultsOfOperationsByReportableSegmentDetails</Role>
      <ShortName>Segments - Schedule of Results of Operations by Reportable Segment (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>70</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R71.htm</HtmlFileName>
      <LongName>996155 - Disclosure - Earnings Per Share - Summary of Basic and Diluted EPS (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureEarningsPerShareSummaryOfBasicAndDilutedEpsDetails</Role>
      <ShortName>Earnings Per Share - Summary of Basic and Diluted EPS (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>71</Position>
    </Report>
    <Report instance="altg-20250930.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R72.htm</HtmlFileName>
      <LongName>996165 - Disclosure - Earnings Per Share - Additional Information (Details)</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://www.altaequipment.com/20250930/taxonomy/role/DisclosureEarningsPerShareAdditionalInformationDetails</Role>
      <ShortName>Earnings Per Share - Additional Information (Details)</ShortName>
      <MenuCategory>Details</MenuCategory>
      <Position>72</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" isDefinitelyFs="true" isUsgaap="true" original="altg-20250930.htm">altg-20250930.htm</File>
    <File>altg-20250930.xsd</File>
  </InputFiles>
  <SupplementalFiles/>
  <BaseTaxonomies>
    <BaseTaxonomy items="1170">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="34">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
