XML 63 R51.htm IDEA: XBRL DOCUMENT
v3.21.2

Selected Balance Sheet Data - Schedule of Other Assets (Parenthetical) (Detail) - USD ($) $ in Thousands | 6 Months Ended
--- | ---
Jun. 30, 2021 | Jun. 30, 2020
Other Assets [Line Items] |  |
Reduction of accrued bonuses and other employee related expenses in settlement of employee notes receivable | $ 10 | $ 0

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

X
- Definition Reduction of accrued bonuses and other employee related expenses in settlement of employee notes receivable. + References No definition available. + Details
Name: | mmi_ReductionOfAccruedBonusesAndOtherEmployeeRelatedExpensesInSettlementOfEmployeeNotesReceivable
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration