Compensation - Compensation Expense Related to Issuance of BGC or Newmark Class A Common Stock and Grants of Exchangeability on BGC Holdings and Newmark Holdings LPUs held by BGC Employees (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
LPUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Issuance of common stock and grants of exchangeability	$ 128,107	$ 84,966	$ 100,948