Compensation - Compensation Expense Related to Limited Partnership Units and Restricted Stock Units (Details) - USD ($)	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	$ 85,918,000	$ 97,031,000	$ 317,281,000
Total compensation expense	124,805,000	122,437,000	301,162,000
Equity-based compensation and allocations of net income to limited partnership units and FPUs	139,747,000	138,312,000	356,345,000
Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Total compensation expense	0	(4,700,000)	(4,600,000)
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	139,747,000	138,312,000	356,345,000
NEWMARK Group Inc Parent | Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award
Limited partnership units amortization	24,620,000	21,807,000	16,795,000
NEWMARK Group Inc Parent | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award
Issuance of common stock and exchangeability expenses	85,918,000	92,308,000	312,718,000
Limited partnership units amortization	14,267,000	8,322,000	(28,351,000)
Allocations of net income to limited partnership units and FPUs	$ 14,942,000	$ 15,875,000	$ 55,183,000