Related Party Transactions - Transactions with Executive Officers and Directors (Barry Gosin) (Details)							3 Months Ended	9 Months Ended
	Sep. 23, 2024 $ / shares shares	Aug. 07, 2024 USD ($) shares	Dec. 31, 2023 shares	Apr. 01, 2023 shares	Mar. 30, 2023 USD ($) shares	Feb. 10, 2023 USD ($) tranche installment $ / shares shares	Sep. 30, 2023 shares	Sep. 30, 2024 USD ($) shares	Sep. 30, 2023 shares	Dec. 13, 2017
Related Party Transaction
Stock repurchased (in shares)	795,376						0		0
Preferred stock, redemption price per share (in dollars per share) | $ / shares	$ 14.19
Share price (in dollars per share) | $ / shares	$ 15.34
Limited partnership units exchange ratio	0.9248							0.4545
Class of warrant or right, exchange rate			14.29%
APSUs
Related Party Transaction
Stock repurchased (in shares)	123,336
PSUs
Related Party Transaction
Stock repurchased (in shares)	611,167
SPUSs
Related Party Transaction
Stock repurchased (in shares)	60,873
Class A Common Stock
Related Party Transaction
Limited partnership units exchange ratio										1
Mr. Gosin
Related Party Transaction
Related party transaction, termination notice, period		6 months
Related party transaction, one time cash payment | $		$ 5,000,000
Related party transaction, annual compensation | $		17,500,000
Related party transaction, annual compensation, salary | $		1,000,000
Related party transaction, annual compensation, cash-based and share-based awards | $		$ 16,500,000
Class of warrant or right, conversion ratio			0.9231	0.9252
Annual cash bonus | $						$ 1,500,000
Mr. Gosin | Class A Common Stock
Related Party Transaction
Issuance of Class A common stock for Newmark RSUs (in shares)					189,024
Class of warrant or right, redeemed | $					$ 3,125,001
Newmark Holdings NPSUs | Mr. Gosin
Related Party Transaction
Share price (in dollars per share) | $ / shares						$ 8.73
Number of conversion rights granted (in shares)		1,694,915						1,145,476
Conversion percentage						25.00%		25.00%
Class of warrant or right percentage								75.00%
Minimum gross revenue threshold | $						$ 10,000,000		$ 10,000,000
Class of warrant or right, rights exchanged (in shares)								1,238,620
Class of warrant or right, rights converted (in shares)			1,145,494	1,145,494
Number of tranches | tranche						4
Class of warrant or right, advance award (in shares)						1,145,475
Related party transaction, upfront advance award, base for calculating number of grants in period | $						$ 10,000,000
Number of installments | installment						3
Conversion percentage, tranche one						25.00%
Conversion percentage, tranche two						25.00%
Conversion percentage, tranche three						25.00%
Conversion percentage, tranche four						25.00%
Newmark Holdings NPSUs | Mr. Gosin | Award Period One
Related Party Transaction
Share-based liabilities paid | $		$ 5,000,000
Newmark Holdings NPSUs | Mr. Gosin | Award Period Two
Related Party Transaction
Share-based liabilities paid | $		15,000,000
Newmark Holdings NPSUs | Mr. Gosin | Award Period Three
Related Party Transaction
Share-based liabilities paid | $		$ 1,500,000
Newmark Holdings PSU | Mr. Gosin
Related Party Transaction
Class of warrant or right, issued upon conversion (in shares)			1,240,901	1,237,644
Exchangeable Newmark Holdings PSUs | Mr. Gosin
Related Party Transaction
Warrants and rights outstanding (in shares)				176,804
Non-Exchangeable Newmark Holdings PSUs | Mr. Gosin
Related Party Transaction
Class of warrant or right, conversion ratio					0.9303
Class of warrant or right, rights exercised (in shares)					203,186