Compensation - Activity Associated with Limited Partnership Units (Details) - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	30,687,954	18,419,613
Number of units, Issued (in shares)	16,092,841	15,402,041
Number of units, Redeemed/exchanged units (in shares)	(3,676,057)	(2,934,984)
Number of units, Forfeited units (in shares)	(727,772)	(198,716)
Ending balance (in shares)	42,376,966	30,687,954
Exchangeable units (in shares)	12,189,148	7,861,359
NEWMARK Group Inc Parent | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	3,900,000
Ending balance (in shares)	3,100,000	3,900,000
Exchangeable partnership units (in shares)	1,500,000	1,500,000
NEWMARK Group Inc Parent | Limited Partnership Units | Employee
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	2,000,000
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	5,459,388	8,663,930
Number of units, Issued (in shares)	1,506	25,032
Number of units, Redeemed/exchanged units (in shares)	(5,459,895)	(3,169,063)
Number of units, Forfeited units (in shares)	(999)	(60,511)
Ending balance (in shares)	0	5,459,388
Exchangeable units (in shares)	0	2,654,749
BGC Holdings, L.P. | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	4,800,000
Ending balance (in shares)		4,800,000
Exchangeable partnership units (in shares)		2,500,000