Related Party Transactions - Transactions with Executive Officers and Directors (Howard Lutnick) (Details) - USD ($)						3 Months Ended		9 Months Ended
	Jan. 02, 2024	May 18, 2023	Apr. 01, 2023	Dec. 28, 2021	Dec. 21, 2021	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Apr. 19, 2019	Apr. 01, 2019
Related Party Transaction
Number of units redeemed (in shares)						2,350,268	3,168,080	7,333,712	6,985,253
Issuance of common stock and exchangeability expenses						$ 30,059,000	$ 15,056,000	$ 78,017,000	$ 42,762,000
Related party transaction, award payment term				3 years
BGC Holdings, L.P.
Related Party Transaction
Number of units redeemed (in shares)						0	11,404	0	127,960
Newmark Holdings Units
Related Party Transaction
Number of units redeemed (in shares)						2,350,268	3,156,676	7,333,712	6,857,293
Howard W. Lutnick
Related Party Transaction
Cash payment	$ 1,250,000
Contingent gross revenue minimum										$ 5,000,000
Class of warrant or right, rights exercised (in shares)					250,000
Howard W. Lutnick | Retention Bonus Agreement
Related Party Transaction
Aggregate cash payments				$ 50,000,000
Howard W. Lutnick | Retention Bonus Agreement, Payment Within Three Days
Related Party Transaction
Aggregate cash payments				20,000,000
Howard W. Lutnick | Retention Bonus Agreement, Payment Within Thirty Days
Related Party Transaction
Aggregate cash payments				$ 10,000,000
Howard W. Lutnick | BGC Holdings, L.P.
Related Party Transaction
Number of units redeemed (in shares)		1,474,930
Issuance of common stock and exchangeability expenses		$ 9,100,000
Howard W. Lutnick | Newmark Holdings Units
Related Party Transaction
Issuance of common stock and exchangeability expenses		$ 7,000,000
Rights for Previously Non-Exchangeable PSUs | Howard W. Lutnick
Related Party Transaction
Warrants and rights outstanding (in shares)	617,262
Class of warrant or right, number of securities called by warrants or rights (in shares)	617,262
Rights for Monetization of Previously Awarded Nonexchangeable PPSUs | Howard W. Lutnick
Related Party Transaction
Warrants and rights outstanding (in shares)	81,275
Class of warrant or right, cash payment called by warrants or rights	$ 1,250,000
Non-Exchangeable Rights for Newmark Holdings PSUs/NPSUs | Howard W. Lutnick
Related Party Transaction
Class of warrant or right, waived (in shares)	617,262
Non-Exchangeable Rights for Newmark Holdings PPSUs | Howard W. Lutnick
Related Party Transaction
Class of warrant or right, waived (in shares)	81,274
Newmark Holdings NPSUs and NNPSUs | Howard W. Lutnick
Related Party Transaction
Class of warrant or right, exercise price of warrants or rights (in dollars per share)											$ 10.05
Newmark Holdings NPSUs | Howard W. Lutnick
Related Party Transaction
Warrants and rights outstanding (in shares)											500,000
Class of warrant or right, number of securities called annually by warrants or rights (in shares)										125,000
Class of warrant or right, rights exchanged (in shares)			125,000
Newmark Holdings NPPSUs | Howard W. Lutnick
Related Party Transaction
Warrants and rights outstanding (in shares)											500,000
Class of warrant or right, number of securities called annually by warrants or rights (in shares)										125,000
Non-Exchangeable Newmark Holdings PSUs | Howard W. Lutnick
Related Party Transaction
Class of warrant or right, number of securities called annually by warrants or rights (in shares)										125,000
Class of warrant or right, rights exchanged (in shares)			125,000
Non-Exchangeable Newmark Holdings PPSUs | Howard W. Lutnick
Related Party Transaction
Class of warrant or right, number of securities called annually by warrants or rights (in shares)										125,000