Compensation - Activity Associated with Limited Partnership Units (Details) - shares	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
NEWMARK Group Inc
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	42,376,966	30,687,954
Number of units, Issued (in shares)	4,819,326	16,092,841
Number of units, Redeemed/exchanged units (in shares)	(596,865)	(3,676,057)
Number of units, Forfeited units (in shares)	(366,197)	(727,772)
Ending balance (in shares)	46,233,230	42,376,966
Exchangeable units (in shares)	13,674,455	12,189,148
NEWMARK Group Inc | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	3,100,000
Ending balance (in shares)	3,000,000	3,100,000
Exchangeable partnership units (in shares)	1,400,000	1,500,000
NEWMARK Group Inc | Limited Partnership Units | Employee
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	2,100,000
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	0	5,459,388
Number of units, Issued (in shares)	0	1,506
Number of units, Redeemed/exchanged units (in shares)	0	(5,459,895)
Number of units, Forfeited units (in shares)	0	(999)
Ending balance (in shares)	0	0
Exchangeable units (in shares)	0	0
BGC Holdings, L.P. | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	0