Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Cantor	Cumulative Effect Period of Adoption Adjustment	Smith Mack	Additional Paid-in Capital	Additional Paid-in Capital Cantor	Additional Paid-in Capital Smith Mack	Treasury Stock	Retained Deficit	Retained Deficit Cumulative Effect Period of Adoption Adjustment	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest in Subsidiaries	Noncontrolling Interest in Subsidiaries Cantor	Noncontrolling Interest in Subsidiaries Cumulative Effect Period of Adoption Adjustment	Noncontrolling Interest in Subsidiaries Smith Mack	Class A Common Stock Common Stock	Class A Common Stock Common Stock Smith Mack	Class B Common Stock Common Stock
Beginning balance at Dec. 31, 2018	$ 855,459				$ 2,217,340			$ (314,240)	$ (1,116,026)		$ (24,465)	$ 88,974				$ 3,417		$ 459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss) available to common stockholders	66,816								43,901			22,915
Other comprehensive gain, net of tax	(13,014)										(8,637)	(4,377)
Equity-based compensation	10,489				7,066							3,419				4
Dividends to common stockholders	(192,442)								(192,442)			0
Earnings distributions to limited partnership interests and other noncontrolling interests	(89,616)											(89,616)
Grant of exchangeability and redemption of limited partnership interests	86,458				56,455							29,853				150
Issuance of Class A common stock (net of costs)	1,116				879							235				2
Redemption of FPUs	(256)											(256)
Repurchase of Class A common stock	(1,236)							(970)				(266)
Forfeitures of Class A common stock	(139)				(12)			(98)				(29)
Contributions of capital to and from Cantor for equity-based compensation		$ (136)				$ (382)							$ 246
Issuance of Class A common stock and RSUs for acquisitions				$ 3,040			$ 4,471								$ (1,442)		$ 11
Other	2,567				3,247							(680)
Ending balance at Dec. 31, 2019	$ 729,106		$ (1,300)		2,289,064			(315,308)	(1,264,567)	$ (883)	(33,102)	48,976		$ (417)		3,584		459
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accounting Standards Update [Extensible Enumeration]	Accounting Standards Update 2016-13 [Member]
Net income (loss) available to common stockholders	$ 50,918								45,062			5,856
Other comprehensive gain, net of tax	4,617										4,172	445
Equity-based compensation	12,672				8,565							4,096				11
Dividends to common stockholders	(60,440)								(60,440)
Earnings distributions to limited partnership interests and other noncontrolling interests	(36,569)											(36,569)
Grant of exchangeability and redemption of limited partnership interests	93,793				61,766							31,895				132
Issuance of Class A common stock (net of costs)	5,505				5,381							120				4
Redemption of FPUs	(102)											(102)
Repurchase of Class A common stock	(6)							(5)				(1)
Contributions of capital to and from Cantor for equity-based compensation		5,519				3,613							1,906
Issuance of Class A common stock and RSUs for acquisitions	1,578				1,664							(90)				4
Other	6,006				5,060							946
Ending 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]
Net income (loss) available to common stockholders	153,488								124,007			29,481
Other comprehensive gain, net of tax	(13,446)										(11,618)	(1,828)
Equity-based compensation	17,924				13,015							4,887				22
Dividends to common stockholders	(15,098)								(15,098)
Earnings distributions to limited partnership interests and other noncontrolling interests	(22,658)											(22,658)
Grant of exchangeability and redemption of limited partnership interests	119,959				69,855							49,524				580
Issuance of Class A common stock (net of costs)	1,510				1,492							14				4
Redemption of FPUs	(408)											(408)
Repurchase of Class A common stock	(365,398)							(307,773)				(57,625)
Forfeitures of Class A common stock	(553)				181			(648)				(86)
Contributions of capital to and from Cantor for equity-based compensation		$ (28,011)				$ (15,429)							$ (12,582)
Issuance of Class A common stock and RSUs for acquisitions				$ 1,160			$ 9,825								$ (8,683)		$ 18
Cantor purchase of Cantor units from BGC Holdings upon redemption of FPUs, 4,408,931 units	7,894											7,894
Acquisition of Futures Exchange Group	(9,022)				(7,616)							(1,406)
Other	4,677				4,699							(22)
Ending balance at Dec. 31, 2021	$ 663,315				$ 2,451,135			$ (623,734)	$ (1,171,919)		$ (40,548)	$ 43,563				$ 4,359		$ 459