Condensed Consolidated Statements of Changes in Equity (Parenthetical) - shares	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019	Sep. 30, 2018
Noncontrolling Interests in Subsidiaries [Member]
BGC's purchase of exchangeable limited partnership units in Newmark Holdings, shares			16,606,726
Class A Common Stock [Member]
Grant of exchangeability, redemption and issuance of limited partnership interests and issuance of common stock, shares	588,972	1,965,195
Repurchase of shares	2,279,373	3,892,405
Equity-based compensation and related issuance, shares			327,746