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v3.22.2

Selected Balance Sheet Data - Schedule of Other Assets (Parenthetical) (Detail) | 6 Months Ended
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Jun. 30, 2022
Other Assets [Line Items] |
Treasury note term | 1 year
Held-to-maturity Securities [Member] |
Other Assets [Line Items] |
Securities, Held-To-Maturity Maturity Date | Sep. 01, 2024

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- Definition Other Assets [Line Items] + References No definition available. + Details
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Namespace Prefix: | mmi_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Treasury note term rate used to determine SARs liability interest accrual rate. + References No definition available. + Details
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Namespace Prefix: | mmi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Date of maturity of investment in debt security measured at amortized cost (held-to-maturity), in YYYY-MM-DD format. + References No definition available. + Details
Name: | us-gaap_HeldtomaturitySecuritiesDebtMaturitiesDate
Namespace Prefix: | us-gaap_
Data Type: | xbrli:dateItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BalanceSheetLocationAxis=us-gaap_HeldtomaturitySecuritiesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |