Condensed Consolidated Statements of Changes in Equity (Unaudited) (Parenthetical)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Repurchase of Class A common stock, shares	999,722
Class A Common Stock [Member]
Equity-based compensation, shares	745,188	1,343,894
Grant of exchangeability and redemption of limited partnership interests, shares	51,683,294	18,024,094
Issuance of Class A common stock (net of costs), shares	2,453,473	4,797,177
Issuance of Class A common stock upon purchase of notes receivable, shares		453,172
Repurchase of Class A common stock, shares	999,722	44,013
Issuance of Contingent and Class A common stock for acquisitions, share	1,086,975	2,119,393
Partnership Units [Member]
Redemption of founding/working partner units	929,053	1,928,069
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units		920,729