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Other Assets - Summary of Non Current Other Assets (Parenthetical) (Detail) $ in Millions | Dec. 31, 2017 USD ($)
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BPF [Member] |
Other Assets [Line Item] |
Business acquisition, deferred tax asset | $ 108.6

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- Definition Other assets. + References No definition available. + Details
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Namespace Prefix: | nmrk_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of deferred tax asset attributable to deductible temporary differences and carryforwards acquired at the acquisition date. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=84161108&loc=d3e4845-128472 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 45 -Paragraph 4 -URI http://asc.fasb.org/extlink&oid=84176650&loc=d3e31917-109318 + Details
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Balance Type: | debit
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |