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
		Mar. 31, 2020	Mar. 31, 2019
Fully diluted earnings per share
Net income available to common stockholders	[1]	$ 5,737	$ 13,680
Allocations of net income (loss) to limited partnership interests in Newmark Holdings, net of tax		3,196	8,288
Net income for fully diluted shares		$ 8,933	$ 21,968
Weighted-average shares:
Common stock outstanding (in shares)		177,545	178,611
Partnership units		84,491	89,991
RSUs (Treasury stock method)		1,370	0
Newmark exchange shares		240	455
Fully diluted weighted-average shares of common stock outstanding (in shares)		263,646	269,057
Fully diluted earnings per share (in usd per share)		$ 0.03	$ 0.08

[1] Includes a reduction for dividends on preferred stock or units in the amount of $2.4 million and $3.2 million for the three months ended March 31, 2020 and 2019, respectively.