Compensation - Compensation Expense Related to Restricted Stock Unit Held by BGC Employees (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Compensation Related Costs [Abstract]
RSU amortization	$ 7,465	$ 5,212	$ 4,576

Share based compensation arrangement by share based payment award restricted stock units amortization.

No definition available.

Name:	bgcp_ShareBasedCompensationArrangementByShareBasedPaymentAwardRestrictedStockUnitsAmortization
Namespace Prefix:	bgcp_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration