Earnings Per Share and Weighted-Average Shares Outstanding - Calculation of Fully Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fully diluted earnings per share:
Net income available to common stockholders	[1]	$ 72,101	$ 85,475	$ 75,703	$ 118,599
Allocations of net income to limited partnership interests in Newmark Holdings, net of tax		31,522	14,025	34,719	3,780
Net income for fully diluted shares		$ 103,623	$ 99,500	$ 110,422	$ 122,379
Weighted-average shares:
Common stock outstanding (in shares)		179,501	177,020	178,527	178,122
Partnership units (units)		86,912	28,466	86,093	5,661
RSUs (Treasury stock method) (units)		155	786	254	1,231
Newmark exchange shares (shares)		225	344	230	399
Fully diluted weighted-average shares of common stock outstanding (in shares)		266,793	206,616	265,104	185,413
Fully diluted earnings per share (in usd per share)		$ 0.39	$ 0.48	$ 0.42	$ 0.66

[1] Includes a reduction for dividends on preferred stock or exchangeable preferred partnership units in the amount of $3.2 million and $8.1 million for the three and nine months ended September 30, 2020, respectively, and $3.2 million and $9.7 million for the three and nine months ended September 30, 2019, respectively (see Note 1 — “Organization and Basis of Presentation”).