Compensation - Summary of the BGC Holdings and Newmark Holdings LPUs held by BGC Employees (Detail) - LPUs - shares	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	112,115,000	137,652,000	102,407,000	79,729,000
Newmark
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	11,051,000	13,202,000	14,607,000	22,113,000
Regular Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	77,610,000
Regular Units | Newmark
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	8,316,000
Preferred Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	34,505,000
Preferred Units | Newmark
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, balance outstanding (in shares)	2,735,000