Consolidated Statements of Changes in Equity - USD ($) $ in Thousands	Total	Common Stock	Common Stock Class A Common Stock	Common Stock Class B Common Stock	Common Stock Contingent Class A Common Stock	Additional Paid-in Capital	Treasury Stock	Retained Earnings	BGC’s Net Investment in Newmark	Noncontrolling Interests
Beginning Balance at Dec. 31, 2016	$ 983,783		$ 0	$ 0	$ 0	$ 0	$ 0	$ 245,877	$ 735,899	$ 2,007
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income	145,096							144,492		604
Distributions to BGC and noncontrolling interests	(190,948)							(190,877)		(71)
Purchase of noncontrolling interests									1,092	(1,092)
Noncontrolling interests in an entity acquired	19,146									19,146
Debt assumed from BGC	(1,387,500)								(1,387,500)
Capital contributions to and from Cantor for equity-based compensation and other	368,418								368,418
Transfer of pre-initial public offering (“IPO”) capital to redeemable partnership interest	(21,096)								(21,096)
Issuance of shares in the Separation (Class A common stock, 115,593,787 shares); (Class B common stock, 15,840,049 shares)			1,156	158		(245,815)			303,187	(58,686)
Proceeds from IPO, net of underwriting discounts and other expenses (Class A common stock, 23,000,000 shares)	295,419		230			295,189
Equity-based compensation (Class A common stock, 600,000 shares)	10,000					10,000
Ending Balance at Dec. 31, 2017	222,318		1,386	158	0	59,374	0	199,492	$ 0	(38,092)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Consolidated net income	191,898							106,732		85,166
Capital contributions to and from Cantor for equity-based compensation and other	45,296					27,920				17,376
Equity-based compensation (Class A common stock, 600,000 shares)	788					788
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)
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) in Newmark Opco	325,478									325,478
Earning distributions to limited partnership interests, redeemable partnership interests, and other noncontrolling interests	(61,796)									(61,796)
Repurchase of shares	(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 [Roll Forward]
Dividends declared and paid per share of common stock (dollars per share)		$ 0.27
Dividends declared per share of common stock (dollars per share)		0.36
Consolidated net income	161,712							117,305		44,407
Dividends to common stockholders	(69,245)							(69,245)
Preferred dividend on exchangeable preferred partnership units								(12,900)		12,900
Grant of exchangeability, redemption and issuance	(1,902)		38		(1,789)	30,607				(30,758)
Earning distributions to limited partnership interests, redeemable partnership interests, and other noncontrolling interests	(73,646)									(73,646)
Repurchase of shares	(42,100)						(34,408)			7,692
Redemption of EPUs										(93,480)
Other	2,487					2,487
Ending Balance at Dec. 31, 2019	$ 940,625		$ 1,608	$ 212	$ 1,461	$ 318,165	$ (34,894)	$ 313,112		$ 340,961
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Dividends declared and paid per share of common stock (dollars per share)		0.39
Dividends declared per share of common stock (dollars per share)		$ 0.40