XML 74 R64.htm IDEA: XBRL DOCUMENT
v3.21.1

Fair Value Measurements - Additional Information (Detail) - USD ($) | 3 Months Ended |
--- | --- | ---
Mar. 31, 2021 | Mar. 31, 2020 | Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Fair value, assets, level 3 transfers, amount | $ 0 | $ 0 |
Contingent and deferred consideration, maximum undiscounted payment | $ 32,000,000.0 |  | $ 33,200,000
Recurring [Member] | Maximum [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Earn-out period for contingent and deferred consideration | 7 years |  |
Recurring [Member] | Minimum [Member] |  |  |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] |  |  |
Earn-out period for contingent and deferred consideration | 1 year |  |

X
- Definition Business combination contingent deferred consideration arrangements earn out period. + References No definition available. + Details
Name: | mmi_BusinessCombinationContingentDeferredConsiderationArrangementsEarnOutPeriod
Namespace Prefix: | mmi_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Business combination contingent deferred consideration arrangements range of outcomes value high. + References No definition available. + Details
Name: | mmi_BusinessCombinationContingentDeferredConsiderationArrangementsRangeOfOutcomesValueHigh
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of transfer of financial instrument classified as an asset into (out of) level 3 of the fair value hierarchy. + References No definition available. + Details
Name: | us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetTransfersNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Details
Name: | us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsRecurringMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_RangeAxis=srt_MinimumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |