Fair Value of Financial Assets and Liabilities - Quantitative Information about Level 3 Fair Value Measurements (Details) $ in Thousands	Mar. 31, 2023 USD ($)	Dec. 31, 2022 USD ($)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 16,259	$ 14,320
Liabilities	9,292	9,378
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration	$ 20,985	$ 8,343
Level 3 \| Minimum \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.040	0.040
Level 3 \| Minimum \| Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.750	0.750
Level 3 \| Maximum \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.118	0.118
Level 3 \| Maximum \| Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	1.000	1.000
Level 3 \| Weighted Average \| Discount rate
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.034	0.051
Level 3 \| Weighted Average \| Probability of meeting earnout and contingencies
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Contingent consideration liability, measurement input	0.993	0.989
Level 3 \| Forward Sale Contracts
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	$ 6,183	$ 11,139
Liabilities	4,487	624
Level 3 \| Rate lock commitments
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Assets	10,076	3,181
Liabilities	$ 4,805	$ 8,754

Amount of liability recognized arising from contingent consideration in a business combination.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (c)(1)
-URI https://asc.fasb.org/extlink&oid=126975305&loc=d3e6927-128479

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 35
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=126966325&loc=d3e6819-128478

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 25
-Paragraph 6
-URI https://asc.fasb.org/extlink&oid=6911189&loc=d3e6408-128476

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Value of input used to measure contingent consideration liability from business combination.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)(2)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as an asset.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4B
-Subparagraph (c)(2)
-URI https://asc.fasb.org/extlink&oid=125515794&loc=SL5624163-113959

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsAssetAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value as of the balance sheet date of derivative instrument not designated as hedging instrument and classified as a liability.

+ References

+ Details

Name:	us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsLiabilityAtFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- 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

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=us-gaap_MeasurementInputDiscountRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MeasurementInputTypeAxis=nmrk_MeasurementInputExpectedEarnoutAndContingenciesRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=nmrk_ForwardSaleContractsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_InterestRateLockCommitmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: