Compensation - Activity Associated with LPU's Held by BGC Employees (Detail) - LPUs - shares	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Number of Units, Balance outstanding at beginning of period (in shares)	110,348,000	112,115,000	137,652,000
Number of Units, Granted (in shares)	9,688,000	27,968,000	34,093,000
Number of Units, Redeemed/exchanged units (in shares)	(119,812,000)	(24,623,000)	(58,832,000)
Number of Units, Forfeited units (in shares)	(224,000)	(5,112,000)	(798,000)
Number of Units, Balance outstanding at end of period (in shares)	0	110,348,000	112,115,000
Newmark Units
Share-based Compensation Arrangement by Share-based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Number of Units, Balance outstanding at beginning of period (in shares)	9,351,000	11,051,000	13,202,000
Number of Units, Granted (in shares)	0	0	0
Number of Units, Redeemed/exchanged units (in shares)	(572,000)	(1,636,000)	(1,881,000)
Number of Units, Forfeited units (in shares)	0	(64,000)	(270,000)
Number of Units, Balance outstanding at end of period (in shares)	8,779,000	9,351,000	11,051,000