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		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fully diluted earnings per share:
Net income available to common stockholders	[1]	$ 70,281	$ 104,406	$ 101,641
Allocations of net income to limited partnership interests in Newmark Holdings, net of tax		0	3,754	3,930
Net income for fully diluted shares		$ 70,281	$ 108,160	$ 105,571
Weighted-average shares:
Common stock outstanding (in shares)		179,106	177,774	157,256
Partnership units (units)		0	5,583	5,717
RSUs (Treasury stock method) (units)		355	1,290	187
Newmark exchange shares ( in shares)		229	369	650
Fully diluted weighted-average shares of common stock outstanding (in shares)		179,690	185,016	163,810
Fully diluted earnings per share (in usd per share)		$ 0.39	$ 0.58	$ 0.64

[1] Includes a reduction for dividends on preferred stock or exchangeable preferred partnership units in the amount of $9.8 million, $12.9 million and $5.1 million for the years ended December 31, 2020, 2019 and 2018, respectively.