Schedule I - Parent Company Only Financial Statements - Statements of Comprehensive Income (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Statement of Income Captions [Line Items]
Net income available to common stockholders	$ 117,305	$ 106,732	$ 144,492
Comprehensive income available to common stockholders	117,305	106,732	144,492
NEWMARK Group Inc Parent
Condensed Statement of Income Captions [Line Items]
Net income available to common stockholders	117,305	106,732	144,492
Total other comprehensive income, net of tax	117,305	106,732	144,492
Comprehensive income available to common stockholders	$ 117,305	$ 106,732	$ 144,492