<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2025"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="alxo-20260227.xsd" xlink:type="simple"/>
    <context id="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001810182</identifier>
        </entity>
        <period>
            <startDate>2026-02-27</startDate>
            <endDate>2026-02-27</endDate>
        </period>
    </context>
    <dei:AmendmentFlag
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_b11fd013-cc22-4ad9-8195-b8d26aac5cd9">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_64487cd3-abd7-44b8-ab7e-98ee791fa3dc">0001810182</dei:EntityCentralIndexKey>
    <dei:DocumentType
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_7d6a814f-e0df-4879-aad5-c33f10075d26">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_481c4b95-cc69-4190-9642-27b8e7a14670">2026-02-27</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_e6d23ef5-3156-404b-baff-2ede11f4cd56">ALX ONCOLOGY HOLDINGS INC.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_002b8742-1eb8-43e0-bcfd-2a38db588a38">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_c3da9858-b8b7-45f6-941c-aa2a568e6ab9">001-39386</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_3fa60420-fcff-4efb-b319-6eed1880f156">85-0642577</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_905f2855-ad05-464b-a574-887c83a9d6ba">323 Allerton Avenue</dei:EntityAddressAddressLine1>
    <dei:EntityAddressCityOrTown
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_7f6694b5-9c01-4bd0-8486-1dcc36109a64">South San Francisco</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_cae279d1-b0dd-45c7-8dd9-25f7b4631914">CA</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_f32664d8-0253-4479-bafc-8e01e5af1ca2">94080</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_5e1f0e74-3ff9-4457-a26f-751d4680ea1f">650</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_1c5cf06d-a82d-4f49-a835-3498c2ca8132">466-7125</dei:LocalPhoneNumber>
    <dei:WrittenCommunications
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_1e7fe064-4db2-4600-87d5-6618c6e9c67a">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_68247243-cfd7-484d-9125-d5d9dec5b00c">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_cd1a9076-b4da-49cd-8570-9c61130fee4e">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_76fa1bfb-6141-4c23-835e-365332498bca">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_e5a212d5-0b05-4c72-b17d-5746d7855d28">Common Stock, par value $0.001 per share</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_36465ed5-94f3-45fc-a413-9d29c161292e">ALXO</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_7236f8b4-7aa3-45e2-b281-f7bb0898de6a">NASDAQ</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="C_ea8c20dc-11c1-42c7-b22a-1818c3fc10fe"
      id="F_f45f9d63-6998-44bb-b9c7-5eb9cda7e147">false</dei:EntityEmergingGrowthCompany>
</xbrl>
