Condensed Consolidated Statements of Changes in Equity (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Repurchase of Class A common stock, shares	965,000
Cantor purchase of Cantor units from BGC Holdings upon redemption of Founding/Working Partner Units, units	2,768,060
Dividends declared per share of common stock	$ 0.01	$ 0.14
Dividends declared and paid per share of common stock	$ 0.01	$ 0.14
Class A Common Stock [Member]
Equity-based compensation, shares	1,367,094	696,507
Grant of exchangeability and redemption of limited partnership interests, shares	10,430,945	2,105,401
Issuance of Class A common stock (net of costs), shares	262,373	71,663
Issuance of Class A common stock and RSUs for acquisitions, shares	251,000	270,000
Repurchase of Class A common stock, shares	964,471	0
Class A Common Stock [Member] | Partnership Units [Member]
Redemption of FPUs	617,208
Class A Common Stock [Member] | Smith Mack [Member]
Issuance of Class A common stock and RSUs for acquisitions, shares	250,575	270,496