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v3.19.3.a.u2

Subsequent Events - Additional Information (Detail) - Subsequent Event [Member] $ in Millions | Jan. 01, 2020 USD ($)
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Subsequent Event [Line Items] |
Total consideration for business acquisitions and other commitments | $ 48.2
Payments for business acquisitions and other commitments | $ 33.6

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- Definition Consideration for commitments to investments sales and financing professionals and business acquisitions. + References No definition available. + Details
Name: | mmi_TotalConsiderationForBusinessAcquisitionsAndOtherCommitments
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Cash outflow for commitments to investments sales and financing professionals and business acquisitions. + References No definition available. + Details
Name: | mmi_TotalPaymentsForBusinessAcquisitionAndOtherCommitments
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |