Compensation - Activity Associated with Limited Partnership Units (Details) - shares	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
NEWMARK Group Inc Parent
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	18,419,613	66,626,185
Number of units, Issued (in shares)	7,694,924	10,143,799
Number of units, Redeemed/exchanged units (in shares)	(447,801)	(58,099,726)
Number of units, Forfeited units (in shares)	(230,411)	(250,645)
Ending balance (in shares)	25,436,325	18,419,613
Exchangeable units (in shares)	2,944,731	2,468,443
NEWMARK Group Inc Parent | Regular units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	24,279,159
NEWMARK Group Inc Parent | Preferred Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	1,157,166
BGC Holdings, L.P.
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Beginning balance (in shares)	8,663,930	54,422,002
Number of units, Issued (in shares)	0	159,057
Number of units, Redeemed/exchanged units (in shares)	(1,217,709)	(45,024,619)
Number of units, Forfeited units (in shares)	(60,511)	(892,510)
Ending balance (in shares)	7,385,710	8,663,930
Exchangeable units (in shares)	2,841,025	3,456,479
BGC Holdings, L.P. | Regular units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	7,309,036
BGC Holdings, L.P. | Preferred Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding
Ending balance (in shares)	76,674