Limited Partnership Interests in Newmark Holdings and BGC Holdings (Details) shares in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2024 shares	Sep. 30, 2024 shares	Sep. 23, 2024	Dec. 13, 2017
Related Party Transaction
Limited partnership units exchange ratio	0.4545	0.4545	0.9248
Payout period for post-termination awards		4 years
Percentage to preferred units	0.6875%
Percentage to preferred units per calendar year		2.75%
Class A Common Stock
Related Party Transaction
Limited partnership units exchange ratio				1
Newmark Holdings Units | Class A Common Stock
Related Party Transaction
Limited partnership units exchange ratio	0.9257	0.9257
Newmark Holdings Units | Class B Common Stock
Related Party Transaction
Exchangeable preferred limited partnership units (in shares)	24.9	24.9