Condensed Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Partnership Units	Cantor	Smith Mack	Additional Paid-in Capital	Additional Paid-in Capital Cantor	Additional Paid-in Capital Smith Mack	Treasury Stock	Retained Deficit	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiaries	Noncontrolling Interest in Subsidiaries Cantor	Noncontrolling Interest in Subsidiaries Smith Mack	Class A Common Stock	Class A Common Stock Partnership Units	Class A Common Stock Smith Mack	Class A Common Stock Common Stock	Class A Common Stock Common Stock Smith Mack	Class B Common Stock	Class B Common Stock Common Stock
Beginning Balance at Dec. 31, 2020	$ 811,297				$ 2,375,113			$ (315,313)	$ (1,280,828)	$ (28,930)	$ 57,061						$ 3,735			$ 459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	78,636								58,956		19,680
Other comprehensive income (loss), net of tax	(2,094)									(1,675)	(419)
Equity-based compensation	6,659				4,564						2,078						17
Dividends to common stockholders	(7,626)								(7,626)
Earnings distributions to limited partnership interests and other noncontrolling interests	(11,405)										(11,405)
Grant of exchangeability and redemption of limited partnership interests	42,784				17,740						24,638						406
Issuance of Class A common stock (net of costs)	673			$ 513	662		$ 4,037				8		$ (3,532)				3	$ 8
Redemption of FPUs	(127)										(127)
Repurchase of Class A common stock	(107,783)							(90,972)			(16,811)
Forfeiture of Class A common stock	(330)				137			(416)			(51)
Contributions of capital to and from Cantor for equity-based compensation			$ (26,290)			$ (14,143)						$ (12,147)
#REF!			5,145									5,145
Other	4,308				4,398						(90)
Ending Balance at Jun. 30, 2021	$ 794,360				2,392,508			(406,701)	(1,229,498)	(30,605)	64,028						4,169			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share of common stock (in dollars per share)	$ 0.02
Common Stock, Dividends, Per Share, Cash Paid	$ 0.02
Equity-based compensation (in shares)	1,727,516
Grant of exchangeability and redemption of limited partnership interests, issuance of shares (in shares)	40,586,915													40,587,000
Issuance of class A common stock (net of costs) (in shares)														265,915					0
Redemption of FPUs (in shares)		661,704
Repurchase of class A common stock (in shares)	17,507,000													17,507,006
Forfeiture of Class A Common Stock (in shares)	100,000													83,765
Issuance of Class A common stock and RSUs for acquisitions (in shares)				787,468										787,000
Cantor purchase of Cantor units from BGC Holdings upon redemption of FPUs (in shares)	2,768,060
Beginning Balance at Mar. 31, 2021	$ 873,813				2,387,075			(318,864)	(1,241,886)	(32,284)	75,455						3,858			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	20,060								16,240		3,820
Other comprehensive income (loss), net of tax	1,860									1,679	181
Equity-based compensation	2,487				1,722						762						3
Dividends to common stockholders	(3,852)								(3,852)
Earnings distributions to limited partnership interests and other noncontrolling interests	(4,958)										(4,958)
Grant of exchangeability and redemption of limited partnership interests	31,948				11,736						19,910						302
Issuance of Class A common stock (net of costs)	130			$ 488	126		2,820				4		(2,338)				0	6
Redemption of FPUs	(108)										(108)
Repurchase of Class A common stock	(103,386)							(87,421)			(15,965)
Forfeiture of Class A common stock	(330)				137			(416)			(51)
Contributions of capital to and from Cantor for equity-based compensation			(27,171)			(14,746)						(12,425)
Other	3,379				3,638						(259)
Ending Balance at Jun. 30, 2021	$ 794,360				2,392,508			(406,701)	(1,229,498)	(30,605)	64,028						4,169			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share of common stock (in dollars per share)	$ 0.01
Common Stock, Dividends, Per Share, Cash Paid	$ 0.01
Equity-based compensation (in shares)	360,422
Grant of exchangeability and redemption of limited partnership interests, issuance of shares (in shares)	30,155,970													30,156,000
Issuance of class A common stock (net of costs) (in shares)														3,542					0
Redemption of FPUs (in shares)		44,496
Repurchase of class A common stock (in shares)	16,543,000													16,542,535
Forfeiture of Class A Common Stock (in shares)	100,000													84,000
Issuance of Class A common stock and RSUs for acquisitions (in shares)				536,893										537,000
Beginning Balance at Dec. 31, 2021	$ 663,315				2,451,135			(623,734)	(1,171,919)	(40,548)	43,563						4,359			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	47,044								40,734		6,310
Other comprehensive income (loss), net of tax	(7,019)									(5,908)	(1,111)
Equity-based compensation	7,989				6,047						1,916						26
Dividends to common stockholders	(7,443)								(7,443)
Earnings distributions to limited partnership interests and other noncontrolling interests	141										141
Grant of exchangeability and redemption of limited partnership interests	50,765			$ 2,710	37,823		2,279				12,825		419				117	12
Issuance of Class A common stock (net of costs)	3,478				3,467						7						4
Redemption of FPUs	(145)										(145)
Repurchase of Class A common stock	(29,387)							(24,753)			(4,634)
Forfeiture of Class A common stock	(17)				(1)			(13)			(3)
Contributions of capital to and from Cantor for equity-based compensation			(1,322)			(994)						(328)
#REF!			947									947
Other	(363)				(363)						0
Ending Balance at Jun. 30, 2022	$ 730,693				2,499,393			(648,500)	(1,138,628)	(46,456)	59,907						4,518			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share of common stock (in dollars per share)	$ 0.02
Common Stock, Dividends, Per Share, Cash Paid	$ 0.02
Equity-based compensation (in shares)														2,570,323
Grant of exchangeability and redemption of limited partnership interests, issuance of shares (in shares)	11,707,619													11,714,000
Issuance of class A common stock (net of costs) (in shares)														343,459					0
Redemption of FPUs (in shares)															585,717
Repurchase of class A common stock (in shares)	8,745,000													8,745,310
Forfeiture of Class A Common Stock (in shares)	4,000													4,419
Issuance of Class A common stock and RSUs for acquisitions (in shares)														1,186,000		1,192,907
Cantor purchase of Cantor units from BGC Holdings upon redemption of FPUs (in shares)	480,175
Beginning Balance at Mar. 31, 2022	$ 735,664				2,481,408			(623,734)	(1,149,657)	(37,123)	59,856						4,455			459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income (loss)	16,343								14,762		1,581
Other comprehensive income (loss), net of tax	(10,814)									(9,333)	(1,481)
Equity-based compensation	1,690				1,274				0		410						6
Dividends to common stockholders	(3,733)								(3,733)
Earnings distributions to limited partnership interests and other noncontrolling interests	(1,436)										(1,436)
Grant of exchangeability and redemption of limited partnership interests	20,718			$ 734	15,290		$ 618				5,378		$ 113				50	$ 3
Issuance of Class A common stock (net of costs)	3,326				3,319						3						4
Redemption of FPUs	(61)										(61)
Repurchase of Class A common stock	(29,387)							(24,753)			(4,634)
Forfeiture of Class A common stock	(17)				(1)			(13)			(3)
Contributions of capital to and from Cantor for equity-based compensation			$ (3,152)			$ (2,386)						$ (766)
#REF!	947										947
Other	(129)				(129)
Ending Balance at Jun. 30, 2022	$ 730,693				$ 2,499,393			$ (648,500)	$ (1,138,628)	$ (46,456)	$ 59,907						$ 4,518			$ 459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared per share of common stock (in dollars per share)	$ 0.01
Common Stock, Dividends, Per Share, Cash Paid	$ 0.01
Equity-based compensation (in shares)														589,235
Grant of exchangeability and redemption of limited partnership interests, issuance of shares (in shares)	5,064,529													5,071,000
Issuance of class A common stock (net of costs) (in shares)														338,503					0
Redemption of FPUs (in shares)															556,329
Repurchase of class A common stock (in shares)	8,745,000													8,745,310
Forfeiture of Class A Common Stock (in shares)	4,000													4,419
Issuance of Class A common stock and RSUs for acquisitions (in shares)														274,000		281,230
Cantor purchase of Cantor units from BGC Holdings upon redemption of FPUs (in shares)	480,175