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Related Party Transactions - Other Related Party Transactions and Cantor Rights to Purchase Cantor Units from Newmark Holdings (Details) ft² in Thousands					1 Months Ended	12 Months Ended
	Jun. 30, 2023 USD ($) shares	Apr. 16, 2023 USD ($) shares	Jun. 28, 2021 USD ($)	Nov. 30, 2018 USD ($)	Jan. 31, 2022 USD ($) ft²	Dec. 31, 2023 USD ($) shares	Dec. 31, 2022 USD ($) shares	Dec. 31, 2021 USD ($)	Dec. 20, 2023 USD ($)	Aug. 10, 2023 USD ($)	Mar. 10, 2022 USD ($)	Mar. 16, 2020 USD ($)	Feb. 26, 2020 USD ($)	Mar. 28, 2019	Nov. 28, 2018 USD ($)	Nov. 06, 2018 USD ($)	Dec. 13, 2017
Related Party Transaction
Long-term debt						$ 547,260,000	$ 547,784,000
Operating lease payments						$ 122,300,000	106,800,000	$ 81,700,000
Due from related party, percentage from sale						10.00%
Limited partnership units exchange ratio						0.4545
Proceeds from sales of partnership interest						$ 0	0	$ 6,898,000
Senior Notes \| 6.125% Senior Notes
Related Party Transaction
Long-term debt						$ 0	$ 547,784,000
Debt instrument face amount																$ 550,000,000
Stated interest rate						6.125%										6.125%
Common Stock
Related Party Transaction
Limited partnership units exchange ratio																1
Class A Common Stock
Related Party Transaction
Limited partnership units exchange ratio																	1
Stock issued (in shares) \| shares						2,307,339	0
Class A Common Stock \| NEWMARK Group Inc Parent
Related Party Transaction
Limited partnership units exchange ratio						0.9231
Related Party
Related Party Transaction
Payables to related parties						$ 6,600,000	$ 9,700,000
Remaining lease terms					6 months
Area of real estate property \| ft²					21
Monthly payment on sublease					$ 81,600
Options to extend leases						3 months
Operating lease payments						$ 700,000	1,000,000
Annual base salary			$ 125,000
Annual discretionary bonus rate, maximum			30.00%
Travel and housing reimbursement			$ 250,000
Related Party \| 6.125% Senior Notes
Related Party Transaction
Stated interest rate														6.125%
Related Party \| Founding Partner Exchange Units
Related Party Transaction
Warrants and rights outstanding (in shares) \| shares						53,168
Related Party \| Founding partner interest
Related Party Transaction
Stock issued (in shares) \| shares	74,026	309,631
Proceeds from sales of partnership interest	$ 310,976	$ 1,282,265
Related Party \| Limited partner interest
Related Party Transaction
Stock issued (in shares) \| shares		38,989
Proceeds from sales of partnership interest		$ 166,364
Cantor Credit Agreement \| Related Party \| Line of Credit
Related Party Transaction
Maximum revolving credit				$ 250,000,000
Basis spread on variable rate				1.00%
Revolving Credit Facility \| Line of Credit
Related Party Transaction
Maximum revolving credit											$ 600,000,000	$ 465,000,000	$ 425,000,000		$ 250,000,000
Long-term debt						$ 380,000,000
Revolving Credit Facility \| Line of Credit \| Cantor Credit Agreement
Related Party Transaction
Maximum revolving credit				$ 250,000,000					$ 150,000,000
Basis spread on variable rate				1.00%
Long-term debt						130,000,000	0		$ 130,000,000
Revolving Credit Facility \| Line of Credit \| Delayed Draw Term Loan
Related Party Transaction
Maximum revolving credit										$ 550,000,000
Long-term debt						$ 417,260,000	$ 0