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Property and Equipment - Additional Information (Detail) - USD ($) $ in Millions | 9 Months Ended
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Sep. 30, 2016 | Sep. 30, 2015
Property, Plant and Equipment [Abstract] |  |
Fully depreciated computer software and hardware and furniture, fixtures and equipment write-off | $ 2.7 | $ 2.6

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- Definition Fully depreciated computer software hardware and furniture fixtures and equipment writeoff. + References No definition available. + Details
Name: | mmi_FullyDepreciatedComputerSoftwareHardwareAndFurnitureFixturesAndEquipmentWriteoff
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_PropertyPlantAndEquipmentAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration