<?xml version="1.0" encoding="utf-8"?>
<xbrl
  xmlns="http://www.xbrl.org/2003/instance"
  xmlns:dei="http://xbrl.sec.gov/dei/2024"
  xmlns:ecd="http://xbrl.sec.gov/ecd/2024"
  xmlns:link="http://www.xbrl.org/2003/linkbase"
  xmlns:xlink="http://www.w3.org/1999/xlink">
    <link:schemaRef xlink:href="ls-20250528.xsd" xlink:type="simple"/>
    <context id="c20250101to20250331">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001849089</identifier>
        </entity>
        <period>
            <startDate>2025-01-01</startDate>
            <endDate>2025-03-31</endDate>
        </period>
    </context>
    <context id="c20240101to20241231">
        <entity>
            <identifier scheme="http://www.sec.gov/CIK">0001849089</identifier>
        </entity>
        <period>
            <startDate>2024-01-01</startDate>
            <endDate>2024-12-31</endDate>
        </period>
    </context>
    <dei:DocumentType
      contextRef="c20250101to20250331"
      id="Fact_a05bac22ec7c4fbfa9c065816c6aa590">DEF 14A</dei:DocumentType>
    <dei:AmendmentFlag
      contextRef="c20250101to20250331"
      id="Fact_74d76d4777eb4abd93235b5782f4340b">false</dei:AmendmentFlag>
    <dei:EntityCentralIndexKey
      contextRef="c20250101to20250331"
      id="Fact_1f33cbaa6e744399a7931cb6979e1aa8">0001849089</dei:EntityCentralIndexKey>
    <dei:EntityRegistrantName
      contextRef="c20250101to20250331"
      id="Fact_97ca5d00bfee4fd986cb09a7f3bb13c5">LAFAYETTE SQUARE USA, INC.</dei:EntityRegistrantName>
    <ecd:InsiderTrdPoliciesProcAdoptedFlag
      contextRef="c20240101to20241231"
      id="Fact_81022c7cf8ee448fa53495b66efb1466">true</ecd:InsiderTrdPoliciesProcAdoptedFlag>
</xbrl>
