Compensation - Compensation Expense Related to Limited Partnership Units and Restricted Stock Units (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	$ 19,121,000	$ 33,330,000	$ 53,601,000	$ 71,211,000
Equity-based compensation and allocations of net income to limited partnership units and FPUs			84,805,000	102,974,000
Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	0	0	0	(2,000,000)
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	29,548,000	44,088,000	84,805,000	102,974,000
NEWMARK Group Inc Parent | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units amortization	5,819,000	5,702,000	18,003,000	15,764,000
NEWMARK Group Inc Parent | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	19,121,000	33,330,000	53,601,000	69,188,000
Allocations of net income to limited partnership units and FPUs	3,076,000	4,875,000	3,439,000	12,808,000
Limited partnership units amortization	$ 1,532,000	$ 181,000	$ 9,762,000	$ 5,214,000