Schedule I - Parent Company Only Financial Statements - Statements of Comprehensive Income (Detail) - USD ($)	3 Months Ended	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Condensed Statement of Income Captions
Consolidated net income	$ 161,712,000	$ 109,277,000	$ 161,712,000	$ 191,898,000
Foreign currency translation adjustments	0	(2,178,000)		0
Comprehensive income, net of tax	161,712,000	107,099,000		191,898,000
Comprehensive income available to common stockholders	$ 117,305,000	77,882,000		106,732,000
NEWMARK Group Inc Parent
Condensed Statement of Income Captions
Consolidated net income		80,060,000	117,305,000	106,732,000
Foreign currency translation adjustments		(1,776,000)	0	0
Comprehensive income, net of tax		78,284,000	117,305,000	106,732,000
Comprehensive income available to common stockholders		$ 78,284,000	$ 117,305,000	$ 106,732,000