Compensation - Activity Associated with Limited Partnership Units (Details) - shares	9 Months Ended	12 Months Ended
	Sep. 30, 2024	Dec. 31, 2023
Newmark Holdings Units
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)	13,265,040	16,092,841
Number of units, Redeemed/exchanged units (in shares)	(4,721,510)	(3,676,057)
Number of units, Forfeited units/other (in shares)	(642,429)	(727,772)
Ending balance (in shares)	50,278,067	42,376,966
Exchangeable units (in shares)	13,211,955	12,189,148
Newmark Holdings Units | 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)	2,700,000	3,100,000
Exchangeable partnership units (in shares)	1,800,000	1,500,000
Newmark Holdings Units | Limited Partnership Units | Employee
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	2,200,000
BGC Holdings Units
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/other (in shares)	0	(999)
Ending balance (in shares)	0	0
Exchangeable units (in shares)	0	0
BGC Holdings Units | Limited Partnership Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	0