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Number of equity instruments other than options outstanding, including both vested and non-vested instruments.

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Compensation - Narrative (Details)	3 Months Ended		6 Months Ended
Compensation - Narrative (Details)	Jun. 30, 2023 USD ($) shares	Jun. 30, 2022 USD ($) shares	Jun. 30, 2023 USD ($) shares	Jun. 30, 2022 USD ($) shares	Dec. 31, 2022 shares	Dec. 31, 2021 shares	Dec. 13, 2017 shares
Share-based Compensation Arrangement by Share-based Payment Award
Shares available for future awards (in shares)	314,000,000		314,000,000
Limited partnership units exchange ratio	0.4545		0.4545
Issuance of common stock and exchangeability expenses \| $	$ 9,897,000	$ 28,898,000	$ 34,480,000	$ 37,881,000
Number of shares vested and converted (in shares)	3,800,000		6,300,000
Unrecognized compensation expense related to unvested RSUs \| $	$ 101,500,000		$ 101,500,000
Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses \| $	$ 0	$ (2,000,000.0)	$ 0	$ (2,000,000.0)
Executives and Non Executives Employees
Share-based Compensation Arrangement by Share-based Payment Award
Limited partners capital account units held by BGC (in shares)	86,000,000		86,000,000
Non Distribution Earning Units
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period			4 years
Unit granted during period (in shares)	1,000,000	800,000	2,000,000	1,700,000
Number of shares vested and converted (in shares)		800,000		1,300,000
Newmark Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio	0.4545		0.4545
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award
Limited partners capital account units held by BGC (in shares)	15,944,838		15,944,838		14,277,213
Limited partnership units outstanding (in shares)	38,437,268		38,437,268		30,687,954	18,419,613
NEWMARK Group Inc Parent \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units outstanding (in shares)	3,459,228		3,459,228		3,900,000
Exchangeable partnership units (in shares)	1,690,266		1,690,266		1,500,000
NEWMARK Group Inc Parent \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses \| $	$ 9,897,000	$ 26,875,000	$ 34,480,000	$ 35,858,000
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units outstanding (in shares)	377,539		377,539		5,459,388	8,663,930
BGC Holdings, L.P. \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units outstanding (in shares)	73,245		73,245		4,800,000
Exchangeable partnership units (in shares)	14,386		14,386		2,500,000
Maximum \| NEWMARK Group Inc Parent \| Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Award vesting period			7 years
Class A Common Stock
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio							1
Class A Common Stock \| NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units exchange ratio	0.9235		0.9235
Newmark Equity Plan \| Class A Common Stock \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award
Shares authorized to be delivered pursuant to awards granted (in shares)							400,000,000
Shares registered to be delivered pursuant to awards granted (in shares)							215,000,000