Consolidated Statements of Changes in Equity (Parenthetical) - $ / shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Equity-based compensation (in shares)	2,167,170	1,133,725	434,694
Grant of exchangeability and redemption of limited partnership interests (in shares)	58,024,858	13,190,311	15,008,431
Repurchase of Class A common stock (in shares)	68,253,000
Cantor purchase of Cantor units from BGC Holdings upon redemption of FPUs (in shares)	4,408,931
Dividends declared per share of common stock (in dollars per share)	$ 0.04	$ 0.17	$ 0.56
Dividends declared and paid per share of common stock (in dollars per share)	$ 0.04	$ 0.17	$ 0.56
Smith Mack
Issuance of Class A common stock and RSUs for acquisitions (in shares)	1,789,018	390,775	1,039,452
Partnership Units
Redemption of FPUs (in shares)	1,198,131	730,141	56,878
Class A Common Stock
Grant of exchangeability and redemption of limited partnership interests (in shares)	58,025,000	13,190,000
Issuance of Class A common stock (net of costs) (in shares)	417,247	390,570	212,711
Repurchase of Class A common stock (in shares)	68,253,498	2,259	233,172
Forfeiture of Class A common stock (in shares)	140,188		22,046
Issuance of Class A common stock and RSUs for acquisitions (in shares)	1,789,000	391,000