Compensation - Compensation Expense Related to Limited Partnership Units and Restricted Stock Units (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	$ 9,897,000	$ 28,898,000	$ 34,480,000	$ 37,881,000
Equity-based compensation and allocations of net income to limited partnership units and FPUs			55,258,000	58,886,000
Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	0	(2,000,000.0)	0	(2,000,000.0)
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award
Equity-based compensation and allocations of net income to limited partnership units and FPUs	19,609,000	41,988,000	55,258,000	58,886,000
NEWMARK Group Inc Parent | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units amortization	6,221,000	5,566,000	12,184,000	10,061,000
NEWMARK Group Inc Parent | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	9,897,000	26,875,000	34,480,000	35,858,000
Allocations of net income to limited partnership units and FPUs	122,000	7,787,000	364,000	7,933,000
Limited partnership units amortization	$ 3,369,000	$ 1,760,000	$ 8,230,000	$ 5,034,000