XML 47 R38.htm IDEA: XBRL DOCUMENT
v3.20.1

Operating Leases - Additional Information (Detail) - USD ($) $ in Millions | Mar. 31, 2020 | Dec. 31, 2019
--- | --- | ---
Leases [Abstract] |  |
Operating lease right-of-use assets | $ 114.5 | $ 111.1
Operating lease right-of-use assets, accumulated amortization | $ 26.0 | $ 20.6

X
- Definition Accumulated Amortization Of Right Of Use Lease Assets + References No definition available. + Details
Name: | mmi_AccumulatedAmortizationOfRightOfUseLeaseAssets
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Operating Lease Right Of Use Asset Gross. + References No definition available. + Details
Name: | mmi_OperatingLeaseRightOfUseAssetGross
Namespace Prefix: | mmi_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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