Compensation - Activity Associated with LPU's Held by BGC Employees (Detail) - LPUs - shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	0	110,348,000	112,115,000
Granted (in shares)	0	9,688,000	27,968,000
Redeemed/exchanged units (in shares)	0	(119,812,000)	(24,623,000)
Forfeited units (in shares)	0	(224,000)	(5,112,000)
Ending balance (in shares)	0	0	110,348,000
Newmark Units
Share-Based Compensation Arrangement by Share-Based Payment Award, Non-Option Equity Instruments, Outstanding [Roll Forward]
Beginning balance (in shares)	8,779,000	9,351,000	11,051,000
Granted (in shares)	0	0	0
Redeemed/exchanged units (in shares)	(5,342,000)	(572,000)	(1,636,000)
Forfeited units (in shares)	(501,000)	0	(64,000)
Ending balance (in shares)	2,936,000	8,779,000	9,351,000