Earnings Per Share and Weighted-Average Shares Outstanding - Calculation of Fully Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fully diluted earnings per share
Net income available to common stockholders	[1]	$ 104,406	$ 101,641	$ 144,492
Allocations of net income (loss) to limited partnership interests in Newmark Holdings, net of tax		3,754	3,930	(27,275)
Net income for fully diluted shares		$ 108,160	$ 105,571	$ 117,217
Weighted-average shares:
Basic weighted-average shares of common stock outstanding (in shares)		177,774,000	157,256,000	133,413,000
Partnership units		5,583,000	5,717,000	4,725,000
RSUs (Treasury stock method)		1,290,000	187,000	237,000
Newmark exchange shares		369,000	650,000	23,000
Fully diluted weighted-average shares of common stock outstanding (in shares)		185,016,000	163,810,000	138,398,000
Fully diluted earnings per share (in usd per share)		$ 0.58	$ 0.64	$ 0.85

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