Limited Partnership Interests in Newmark Holdings and BGC Holdings (Details) shares in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2024 shares	Dec. 31, 2024 shares	Oct. 23, 2024	Sep. 23, 2024	Dec. 13, 2017
Related Party Transaction
Limited partnership units exchange ratio	0.4545	0.4545	0.9257	0.9248
Payout period for post-termination awards		4 years
Percentage to preferred units	0.6875%	2.75%
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	0.9279	0.9279
Newmark Holdings Units | Class B Common Stock
Related Party Transaction
Exchangeable preferred limited partnership units (in shares)	25.6	25.6