Consolidated Statements Of Changes In Equity (USD $) In Thousands, unless otherwise specified	Class A Common Stock [Member]	Class B Common Stock [Member]	Additional Paid-In Capital [Member]	Contingent Class A Common Stock [Member]	Treasury Stock [Member]	Retained Earnings (Deficit) [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Non Controlling Interest In Subsidiaries [Member]	Total
Balance at Dec. 31, 2008	$ 617	$ 301	$ 271,161		$ (81,845)	$ 1,958	$ (3,942)	$ 152,952	$ 341,202
Comprehensive income:
Consolidated net income						20,025		20,788	40,813
Other comprehensive (loss) income, net of tax:
Change in cumulative translation adjustment							3,013	165	3,178
Unrealized gain (loss) on securities available for sale							893	(301)	592
Comprehensive income						20,025	3,906	20,652	44,583
Equity-based compensation	8		12,126						12,134
Dividends to stockholders						(24,171)			(24,171)
Earnings distributions to limited partnership interests								(32,700)	(32,700)
Issuance of Class A common stock upon exchange of founding/working partner units	44		9,606					2,550	12,200
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units								195	195
Repurchase of Class A common stock					(7,911)				(7,911)
Re-allocation of equity due to additional investment by founding/working partners								(11,434)	(11,434)
Conversion of Class B common stock to Class A common stock	37	(37)
Other	1		(12)			17		(26)	(20)
Balance at Dec. 31, 2009	707	264	292,881		(89,756)	(2,171)	(36)	132,189	334,078
Comprehensive income:
Consolidated net income						21,162		24,210	45,372
Other comprehensive (loss) income, net of tax:
Change in cumulative translation adjustment							(709)	(440)	(1,149)
Unrealized gain (loss) on securities available for sale							(232)	(105)	(337)
Comprehensive income						21,162	(941)	23,665	43,886
Equity-based compensation	8		7,724						7,732
Dividends to stockholders						(42,606)			(42,606)
Grant of exchangeability to limited partnership units								28,721	28,721
Earnings distributions to limited partnership interests								(45,192)	(45,192)
Issuance of Class A common stock upon exchange of founding/working partner units	52		10,644					5,627	16,323
Cantor purchase of Cantor units from BGC Holdings upon redemption of founding/working partner units								8,031	8,031
Cantor exchange of Cantor units for Class A common stock	37		6,144					(6,181)
Issuance of Class A common stock (net of costs) upon exchange/redemption of limited partnership units	45		26,439					(26,255)	229
Issuance of Class A common stock (net of costs)	26		15,134						15,160
Redemption of founding/working partner units								(10,292)	(10,292)
Repurchase of Class A common stock					(19,871)				(19,871)
Capital contribution by founding/working partners with respect to Charity Day			7,403						7,403
Re-allocation of equity due to additional investment by founding/working partners								(21,681)	(21,681)
Proceeds from exercise of stock options, net of tax			463						463
Conversion of Class B common stock to Class A common stock	6	(6)
Issuance of contingent Class A common stock and limited partnership units for acquisitions				3,171				3,566	6,737
Other			(5)			(1)		2,741	2,735
Balance at Dec. 31, 2010	881	258	366,827	3,171	(109,627)	(23,616)	(977)	94,939	331,856
Comprehensive income:
Consolidated net income						20,137		18,223	38,360
Other comprehensive (loss) income, net of tax:
Change in cumulative translation adjustment							(3,471)	(508)	(3,979)
Unrealized gain (loss) on securities available for sale							696	(25)	671
Comprehensive income						20,137	(2,775)	17,690	35,052
Equity-based compensation	19		4,337					4,365	8,721
Dividends to stockholders						(77,244)			(77,244)
Grant of exchangeability to limited partnership units	123		79,928					31,836	111,887
Earnings distributions to limited partnership interests								(69,816)	(69,816)
Issuance of Class A common stock (net of costs) upon exchange/redemption of limited partnership units	39		14,774					11,952	26,765
Issuance of Class A common stock upon exchange of Cantor units	90		8,317					(8,407)
Issuance Of Class B common stock upon exchange of Cantor units		90	8,317					(8,407)
Redemption of founding/working partner units			(395)					(531)	(926)
Repurchase of Class A common stock					(243)			(149)	(392)
Capital contribution by founding/working partners with respect to Charity Day			5,130					3,046	8,176
Re-allocation of equity due to additional investment by founding/working partners								(6,121)	(6,121)
Purchase of capped call, net of tax			(6,219)					(3,692)	(9,911)
Equity component of convertible debt, net of tax			10,073					5,980	16,053
Acquisition of CantorCO2e, L.P.			(1,255)					(745)	(2,000)
Issuance of contingent Class A common stock for acquisitions			236	16,962				9,580	26,778
Newmark noncontrolling interest								14,384	14,384
Other			(701)			(3)		2,140	1,436
Balance at Dec. 31, 2011	$ 1,152	$ 348	$ 489,369	$ 20,133	$ (109,870)	$ (80,726)	$ (3,752)	$ 98,044	$ 414,698