Limited Partnership Interests in BGC Holdings and Newmark Holdings - Narrative (Detail) shares in Millions	6 Months Ended
	Jun. 30, 2023 installment partnership shares
Related Party Transaction [Line Items]
Number of operating partnerships | partnership	2
Number of installments | installment	4
LPUs
Related Party Transaction [Line Items]
Limited partnership interests exchange ratio	0.9235
Newmark Holdings
Related Party Transaction [Line Items]
Calculation of contribution ratio, denominator	2.2
Limited partnership interest, conversion ratio	1
Percentage of preferred partnership units awarded	0.6875%
Percentage of preferred partnership units awarded per calendar year	2.75%
BGC Holdings
Related Party Transaction [Line Items]
Limited partnership interest, conversion ratio	1
Percentage of preferred partnership units awarded	0.6875%
Percentage of preferred partnership units awarded per calendar year	2.75%
Cantor rights to purchase exchangeable units
Related Party Transaction [Line Items]
Right to exchange from Class A to Class B common stock (up to) (in shares) | shares	23.6