CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY - USD ($) $ in Thousands	Total	Cumulative Effect, Period of Adoption, Adjustment	Common Stock	Common Stock Common Class A	Common Stock Common Class B	Common Stock Contingent Class A Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	Retained Earnings Cumulative Effect, Period of Adoption, Adjustment	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Noncontrolling Interests Cumulative Effect, Period of Adoption, Adjustment
Beginning balance at Dec. 31, 2017	$ 222,318	$ 18,805		$ 1,386	$ 158	$ 0	$ 59,374	$ 0	$ 199,492	$ 16,463		$ (38,092)	$ 2,342
Increase (Decrease) in Stockholders' Equity
Consolidated net income	191,898								106,732			85,166
Reduction of earning distributions	2,144								2,144
Dividends to common stockholders	(41,788)								(41,788)
Preferred dividend on exchangeable preferred partnership units	(5,091)								(5,091)
Capital contributions to and from Cantor for equity-based compensation and other	45,296						27,920					17,376
Equity-based compensation and related issuance of Class A common stock	788						788
BGC's purchase of 16,606,726 exchangeable limited partnership units in Newmark Holdings	241,960											241,960
Exchange of 14,831,234 exchangeable limited partnership units in Newmark Holdings and 6,903,876 limited partnership units in Newmark OpCo into an aggregate of 16,292,623 Class A and 5,445,488 Class B shares of Newmark common stock distributed in the Spin-Off and reallocation of capital	0			163	54	(752)	194,614					(194,079)
Grant of exchangeability, redemption and issuance	106,200			21			6,009					100,170
Issuance of exchangeable preferred partnership units ("EPUs")	325,478											325,478
Earning distributions to limited partnership interests, redeemable partnership interests, and other noncontrolling interests	(61,796)											(61,796)
Repurchase of shares of Class A common stock	(486)							(486)
Issuance of contingent limited partnership units	17,279					4,002						13,277
Other	(6,206)						(3,634)					(2,572)
Ending balance at Dec. 31, 2018	1,056,799			1,570	212	3,250	285,071	(486)	277,952			489,230
Increase (Decrease) in Stockholders' Equity
Consolidated net income	161,712								117,305			44,407
Dividends to common stockholders	(69,245)								(69,245)
Preferred dividend on exchangeable preferred partnership units	0								(12,900)			12,900
Grant of exchangeability, redemption and issuance	(1,902)		$ (1,789)	38			30,607					(30,758)
Earning distributions to limited partnership interests, redeemable partnership interests, and other noncontrolling interests	(73,646)											(73,646)
Repurchase of shares of Class A common stock	(42,100)							(34,408)				(7,692)
Redemption of EPU's	(93,480)											(93,480)
Other	2,487						2,487
Ending balance at Dec. 31, 2019	940,625	$ (21,113)		1,608	212	1,461	318,165	(34,894)	313,112	$ (17,458)		340,961	$ (3,655)
Increase (Decrease) in Stockholders' Equity
Consolidated net income	109,277								80,060			29,217
Foreign currency translation adjustments	(2,178)										$ (1,776)	(402)
Dividends to common stockholders	(23,171)								(23,171)
Preferred dividend on exchangeable preferred partnership units	0								(9,779)			9,779
Grant of exchangeability, redemption and issuance	28,773			68			24,747					3,958
Earning distributions to limited partnership interests, redeemable partnership interests, and other noncontrolling interests	(22,365)											(22,365)
Repurchase of shares of Class A common stock	(6,817)							(5,637)				(1,180)
Issuance and redemption of limited partnership units including contingent units						111	266					(377)
Restricted stock units compensation	11,290						7,648					3,642
Redemption of EPU's	(93,480)											(93,480)
Other	306						624				(318)
Ending balance at Dec. 31, 2020	$ 921,147			$ 1,676	$ 212	$ 1,572	$ 351,450	$ (40,531)	$ 342,764		$ (2,094)	$ 266,098