Compensation - Activity Associated with Limited Partnership Units Awarded to BGC Employees (Detail) - LPUs - shares shares in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, redeemed (in shares)	24,079	17,782	17,709
BGC Holdings LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, redeemed (in shares)	23,001	16,618	17,209
Newmark Holdings LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of units, redeemed (in shares)	1,078	1,164	500