<?xml version='1.0' encoding='utf-8'?>
<FilingSummary>
  <Version>3.26.1</Version>
  <ProcessingTime/>
  <ReportFormat>html</ReportFormat>
  <ContextCount>16</ContextCount>
  <ElementCount>27</ElementCount>
  <EntityCount>1</EntityCount>
  <FootnotesReported>false</FootnotesReported>
  <SegmentCount>8</SegmentCount>
  <ScenarioCount>0</ScenarioCount>
  <TuplesReported>false</TuplesReported>
  <UnitCount>1</UnitCount>
  <MyReports>
    <Report instance="d94228ddef14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R1.htm</HtmlFileName>
      <LongName>995100 - Document - Cover</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/dei/role/document/Cover</Role>
      <ShortName>Cover</ShortName>
      <MenuCategory>Cover</MenuCategory>
      <Position>1</Position>
    </Report>
    <Report instance="d94228ddef14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R2.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>2</Position>
    </Report>
    <Report instance="d94228ddef14a.htm">
      <IsDefault>false</IsDefault>
      <HasEmbeddedReports>false</HasEmbeddedReports>
      <HtmlFileName>R3.htm</HtmlFileName>
      <LongName>995447 - Disclosure - Insider Trading Policies and Procedures</LongName>
      <ReportType>Sheet</ReportType>
      <Role>http://xbrl.sec.gov/ecd/role/InsiderTradingPoliciesProc</Role>
      <ShortName>Insider Trading Policies and Procedures</ShortName>
      <MenuCategory>Notes</MenuCategory>
      <Position>3</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="DEF 14A" isProxy="true" isUsgaap="true" original="d94228ddef14a.htm">d94228ddef14a.htm</File>
    <File>mmi-20251231.xsd</File>
  </InputFiles>
  <SupplementalFiles>
    <File>g94228dsp001.jpg</File>
    <File>g94228dsp002.jpg</File>
    <File>g94228g00a02.jpg</File>
    <File>g94228g01a04.jpg</File>
    <File>g94228g01a05.jpg</File>
    <File>g94228g03g34.jpg</File>
    <File>g94228g03t40.jpg</File>
    <File>g94228g07e68.jpg</File>
    <File>g94228g18j99.jpg</File>
    <File>g94228g28n29.jpg</File>
    <File>g94228g29s99.jpg</File>
    <File>g94228g30x88.jpg</File>
    <File>g94228g38h67.jpg</File>
    <File>g94228g39o59.jpg</File>
    <File>g94228g44q46.jpg</File>
    <File>g94228g46d16.jpg</File>
    <File>g94228g48v37.jpg</File>
    <File>g94228g51i15.jpg</File>
    <File>g94228g52f44.jpg</File>
    <File>g94228g64m21.jpg</File>
    <File>g94228g65j46.jpg</File>
    <File>g94228g68t00.jpg</File>
    <File>g94228g69q66.jpg</File>
    <File>g94228g77u64.jpg</File>
    <File>g94228g80f39.jpg</File>
    <File>g94228g91a01.jpg</File>
    <File>g94228g91b02.jpg</File>
    <File>g94228g91c03.jpg</File>
    <File>g94228g91d04.jpg</File>
    <File>g94228g91e05.jpg</File>
    <File>g94228g91f06.jpg</File>
    <File>g94228g91g07.jpg</File>
    <File>g94228g91h08.jpg</File>
    <File>g94228g92m41.jpg</File>
    <File>g94228g92n47.jpg</File>
    <File>g94228g96v60.jpg</File>
  </SupplementalFiles>
  <BaseTaxonomies>
    <BaseTaxonomy items="5">http://fasb.org/us-gaap/2025</BaseTaxonomy>
    <BaseTaxonomy items="4">http://xbrl.sec.gov/dei/2025</BaseTaxonomy>
    <BaseTaxonomy items="63">http://xbrl.sec.gov/ecd/2025</BaseTaxonomy>
  </BaseTaxonomies>
  <HasPresentationLinkbase>false</HasPresentationLinkbase>
  <HasCalculationLinkbase>false</HasCalculationLinkbase>
</FilingSummary>
