Limited Partnership Interests in Newmark Holdings and BGC Holdings (Details) shares in Millions	3 Months Ended
	Mar. 31, 2026 shares	Feb. 18, 2025	Dec. 13, 2017
Related Party Transaction
Limited partnership units exchange ratio	0.4545	0.9279
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	0.9270
Newmark Holdings Units | Class B Common Stock
Related Party Transaction
Exchangeable preferred limited partnership units (in shares)	18.9