Compensation - Compensation Expense Related to Limited Partnership Units and Restricted Stock Units (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	$ 36,458	$ 35,499	$ 142,333
Equity-based compensation and allocations of net income to limited partnership units and FPUs	130,759	258,836	224,644
Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	32,583	146,215	37,000
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award
Equity-based compensation and allocations of net income to limited partnership units and FPUs	130,759	258,836	224,644
NEWMARK Group Inc Parent \| Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units amortization	12,565	5,204	1,787
NEWMARK Group Inc Parent \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	69,041	181,714	179,333
Allocations of net income to limited partnership units and FPUs	30,461	50,410	51,462
Limited partnership units amortization	$ 18,692	$ 21,508	$ (7,938)

Common Stock, Exchangeability Granted, Issued, Expense

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- Definition

Equity based compensation and allocation of net income to limited partnership units and FPUs

+ References

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- Definition

Amount of equity impact of cash distribution declared to unit-holder of limited partnership (LP).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.3-04)
-URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770

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- Definition

Amount of expense for employee benefit and equity-based compensation.

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