Consolidated Statements of Changes in Equity (USD $) In Thousands	Total	Additional Paid-in Capital [Member]	Contingent Class A Common Stock [Member]	Treasury Stock [Member]	Retained Earnings (Deficit) [Member]	Accumulated Other Comprehensive Income (loss) [Member]	Noncontrolling Interest in Subsidiaries [Member]	Class A Common Stock [Member]	Class B Common Stock [Member]
Beginning Balance at Dec. 31, 2011	$ 414,698	$ 489,369	$ 20,133	$ (109,870)	$ (80,726)	$ (3,752)	$ 98,044	$ 1,152	$ 348
Consolidated net income	35,513				23,864		11,649
Other comprehensive gain (loss), net of tax	(533)					(430)	(103)
Equity-based compensation	5,406	2,798					2,595	13
Dividends to common stockholders	(90,590)				(90,590)
Earnings distributions to limited partnership interests and other noncontrolling interests	(89,963)						(89,963)
Grant of exchangeability and redemption of limited partnership interests	131,609	65,593					65,836	180
Issuance of Class A common stock (net of costs)	26,068	17,123					8,897	48
Issuance of Class A common stock upon purchase of notes receivable	3,055	1,991					1,059	5
Redemption of FPUs	(10,608)	(6,903)					(3,705)
Repurchase of Class A common stock	(337)			(220)			(117)
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units	2,732						2,732
Re-allocation of equity due to additional investment by founding/working partners	(1,378)						(1,378)
Issuance of contingent and Class A common stock for acquisitions	9,026	7,477	(1,651)				3,179	21
Purchases of Newmark noncontrolling interest	(7,243)	(2,112)	386				(5,517)
Other	(43)	45					(88)
Ending Balance at Dec. 31, 2012	427,412	575,381	18,868	(110,090)	(147,452)	(4,182)	93,120	1,419	348
Consolidated net income	173,755				70,924		102,831
Other comprehensive gain (loss), net of tax	(2,191)					(1,878)	(313)
Equity-based compensation	4,618	2,809					1,800	9
Dividends to common stockholders	(91,395)				(91,395)
Earnings distributions to limited partnership interests and other noncontrolling interests	(89,482)						(89,482)
Grant of exchangeability and redemption of limited partnership interests	293,932	151,551					141,821	560
Issuance of Class A common stock (net of costs)	6,009	4,133					1,865	11
Redemption of FPUs	(2,050)						(2,050)
Repurchase of Class A common stock	(15,528)			(11,663)			(3,865)
Re-allocation of equity due to additional investment by founding/working partners	(938)						(938)
Issuance of contingent and Class A common stock for acquisitions	1,776	9,493	(6,817)				(927)	27
Purchases of Newmark noncontrolling interest	(9,367)	(2,540)					(6,827)
Other	6,196	4,851					1,344	1
Ending Balance at Dec. 31, 2013	702,747	745,678	12,051	(121,753)	(167,923)	(6,060)	238,379	2,027	348
Consolidated net income	(3,839)				4,135		(7,974)
Other comprehensive gain (loss), net of tax	12,301					10,363	1,938
Equity-based compensation	3,332	2,275					1,047	10
Dividends to common stockholders	(105,132)				(105,132)
Earnings distributions to limited partnership interests and other noncontrolling interests	(55,821)						(55,821)
Grant of exchangeability and redemption of limited partnership interests	90,067	59,207					30,741	119
Issuance of Class A common stock (net of costs)	361	275					86
Redemption of FPUs	(2,359)						(2,359)
Repurchase of Class A common stock	(102,720)	1,011		(79,205)			(24,526)
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units and subsequent repurchases by BGC Holdings, 3,142,257 units	(13,716)						(13,716)
Re-allocation of equity due to additional investment by founding/working partners	(110)						(110)
Issuance of Class A common stock for acquisitions	7,000	8,976	(3,635)				1,640	19
Issuance of contingent shares and limited partnership interests in connection with acquisitions	50,907		38,967				11,940
Purchases of Newmark noncontrolling interest	(403)	(234)					(169)
Other	(693)	(30)					(690)	27
Ending Balance at Dec. 31, 2014	$ 581,922	$ 817,158	$ 47,383	$ (200,958)	$ (268,920)	$ 4,303	$ 180,406	$ 2,202	$ 348