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Limited Partnership Interests in BGC Holdings and Newmark Holdings - Additional Information (Detail) - shares
shares in Millions
 3 Months Ended 12 Months Ended
Nov. 23, 2018
Jun. 05, 2015
Dec. 31, 2021
Sep. 30, 2021
Jun. 30, 2021
Mar. 31, 2021
Dec. 31, 2021
Noncontrolling Interest [Abstract]              
Number of operating partnerships           2  
Limited partnership interest contribution ratio           45.45%  
Limited partnership interests Exchange Ratio           93.65%  
Payout period for post-termination awards           four equal yearly installments  
Percentage to preferred units           0.6875%  
Common stock exchangeable basis           one-for-one basis  
CF Group Management, Inc. [Member]              
Noncontrolling Interest [Abstract]              
Number of shares, right to exchange from Class A to Class B common stock 0.7 34.6       23.6  
Cantor Rights to Purchase Exchangeable Units [Member]              
Noncontrolling Interest [Abstract]              
Number of shares, right to exchange from Class A to Class B common stock 10.3            
Common stock exchangeable basis           one-for-one  
Cantor Rights to Purchase Exchangeable Units [Member] | Maximum [Member]              
Noncontrolling Interest [Abstract]              
Number of shares, right to exchange from Class A to Class B common stock   34.6       23.6  
Scenario Forecast [Member]              
Noncontrolling Interest [Abstract]              
Percentage to preferred units     0.6875% 0.6875% 0.6875%   2.75%