<?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:sgu="http://www.stargrouplp.com/20260210"
  xmlns:us-gaap="http://fasb.org/us-gaap/2025"
  xmlns:xbrldi="http://xbrl.org/2006/xbrldi"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="sgu-20260210.xsd" xlink:type="simple"/>
    <context id="C_e726ff9a-bcb0-42c0-941d-7102ae28385c">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001002590</identifier>
        </entity>
        <period>
            <startDate>2026-02-10</startDate>
            <endDate>2026-02-10</endDate>
        </period>
    </context>
    <context id="C_ea4b2235-c401-4f94-bef0-5ffaf13adee0">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001002590</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">sgu:CommonUnitPurchaseRightsMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2026-02-10</startDate>
            <endDate>2026-02-10</endDate>
        </period>
    </context>
    <context id="C_45a41707-1961-480b-9094-e8989cb59f35">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001002590</identifier>
            <segment>
                <xbrldi:explicitMember dimension="us-gaap:StatementClassOfStockAxis">sgu:CommonUnitsMember</xbrldi:explicitMember>
            </segment>
        </entity>
        <period>
            <startDate>2026-02-10</startDate>
            <endDate>2026-02-10</endDate>
        </period>
    </context>
    <dei:EntityCentralIndexKey
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_1dfe0b93-5fab-427c-a595-b4e681a46eab">0001002590</dei:EntityCentralIndexKey>
    <dei:AmendmentFlag
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_b0008284-d79f-4d56-89c5-9fd564fa3532">false</dei:AmendmentFlag>
    <dei:DocumentType
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_7d1da289-3ac2-4fa9-a2f1-0c606c520840">8-K</dei:DocumentType>
    <dei:DocumentPeriodEndDate
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_8fdc60f3-f16a-4ea0-a180-0d9710f79053">2026-02-10</dei:DocumentPeriodEndDate>
    <dei:EntityRegistrantName
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_7d3f2c2c-3d87-43ed-b039-02f3125d0879">STAR GROUP, L.P.</dei:EntityRegistrantName>
    <dei:EntityIncorporationStateCountryCode
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_c6f689eb-2dce-4225-b3a8-a305655f61a1">DE</dei:EntityIncorporationStateCountryCode>
    <dei:EntityFileNumber
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_c98e0e42-39b4-49a8-a1f1-41e6eb2a7683">001-14129</dei:EntityFileNumber>
    <dei:EntityTaxIdentificationNumber
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_e15a2750-e687-44c7-918d-37157fe11405">06-1437793</dei:EntityTaxIdentificationNumber>
    <dei:EntityAddressAddressLine1
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_3a941e1e-0968-49f0-8b4d-21327e74c40a">9 West Broad Street</dei:EntityAddressAddressLine1>
    <dei:EntityAddressAddressLine2
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_96812bd6-7aad-49da-97b2-40d15cb8aee2">Suite 310</dei:EntityAddressAddressLine2>
    <dei:EntityAddressCityOrTown
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_4818adc4-f0ce-420b-9aff-121514b6b7cb">Stamford</dei:EntityAddressCityOrTown>
    <dei:EntityAddressStateOrProvince
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_68bc74b5-234a-40d9-b33c-eed13b980a56">CT</dei:EntityAddressStateOrProvince>
    <dei:EntityAddressPostalZipCode
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_faf35b1f-86f4-4ceb-98a9-8fc429661427">06902</dei:EntityAddressPostalZipCode>
    <dei:CityAreaCode
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_bbc4b5ed-1cf1-4a6a-854b-c60e3b9fc0e5">(203)</dei:CityAreaCode>
    <dei:LocalPhoneNumber
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_08620a7a-68fa-4333-887b-3975e6e1fa3c">328-7310</dei:LocalPhoneNumber>
    <dei:EntityInformationFormerLegalOrRegisteredName
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_02576c81-b886-4af1-b592-f41d264e3bed">Not Applicable</dei:EntityInformationFormerLegalOrRegisteredName>
    <dei:WrittenCommunications
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_1d63f79e-14c2-4e8f-941b-6539f5782c74">false</dei:WrittenCommunications>
    <dei:SolicitingMaterial
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_77a973b3-5aa3-473f-80a3-06bdfee13782">false</dei:SolicitingMaterial>
    <dei:PreCommencementTenderOffer
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_2ccb3da3-3876-451b-9bb7-5395c6c756d3">false</dei:PreCommencementTenderOffer>
    <dei:PreCommencementIssuerTenderOffer
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_f960266d-4bc9-431b-b21b-1e7312f2984a">false</dei:PreCommencementIssuerTenderOffer>
    <dei:Security12bTitle
      contextRef="C_45a41707-1961-480b-9094-e8989cb59f35"
      id="F_428c0821-abf9-4c5b-9be1-4bfe6026336e">Common Units</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="C_45a41707-1961-480b-9094-e8989cb59f35"
      id="F_b0449383-d946-4fd6-a877-62dbb9aec749">SGU</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="C_45a41707-1961-480b-9094-e8989cb59f35"
      id="F_7b5157f3-4a2e-44e0-bb45-70eab000cbef">NYSE</dei:SecurityExchangeName>
    <dei:Security12bTitle
      contextRef="C_ea4b2235-c401-4f94-bef0-5ffaf13adee0"
      id="F_02de03e5-a127-4fb3-9a47-cbdccebf29d8">Common Unit Purchase Rights</dei:Security12bTitle>
    <dei:TradingSymbol
      contextRef="C_ea4b2235-c401-4f94-bef0-5ffaf13adee0"
      id="F_d7edb301-00cf-4f11-8270-8093b80d2469">N/A</dei:TradingSymbol>
    <dei:SecurityExchangeName
      contextRef="C_ea4b2235-c401-4f94-bef0-5ffaf13adee0"
      id="F_bc908611-0ac9-40b7-bedf-f0c28d267ec2">NYSE</dei:SecurityExchangeName>
    <dei:EntityEmergingGrowthCompany
      contextRef="C_e726ff9a-bcb0-42c0-941d-7102ae28385c"
      id="F_988d94d0-e7e5-4f6c-9d5a-3e215d5b9c65">false</dei:EntityEmergingGrowthCompany>
</xbrl>
