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Limited Partnership Interests in BGC Holdings and Newmark Holdings - Additional Information (Detail) - shares shares in Millions |  |  | 3 Months Ended | 9 Months Ended | 12 Months Ended
--- | --- | --- | --- | --- | ---
Nov. 23, 2018 | Jun. 05, 2015 | Dec. 31, 2020 | Sep. 30, 2020 | Jun. 30, 2020 | Mar. 31, 2020 | Sep. 30, 2018 | Dec. 31, 2020 | Dec. 31, 2019
Noncontrolling Interest [Abstract] |  |  |  |  |  |  |  |  |
Number of operating partnerships |  |  |  |  |  |  |  | 2 |
Limited partnership interest contribution ratio |  |  |  |  |  |  |  | 45.45% |
Limited partnership interests Exchange Ratio |  |  |  |  |  |  |  | 93.79% |
Payout period for post-termination awards |  |  |  |  |  |  |  | four equal yearly installments |
Percentage to preferred units |  |  | 0.6875% | 0.6875% | 0.6875% | 0.6875% |  | 2.75% |
Distribution ratio |  |  |  |  |  |  | 45.45% | 46.3895% |
Common stock exchangeable basis |  |  |  |  |  |  |  | one-for-one basis |
Newmark [Member] |  |  |  |  |  |  |  |  |
Noncontrolling Interest [Abstract] |  |  |  |  |  |  |  |  |
Common stock exchangeable basis |  |  |  |  |  |  |  | one-for-one |
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

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- Definition Common stock exchangeable basis. + References No definition available. + Details
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- Definition Limited partnership interest contribution ratio. + References No definition available. + Details
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- Definition Limited partnership interest, distribution ratio. + References No definition available. + Details
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- Definition Limited partnership interests exchange ratio, subject to adjustment. + References No definition available. + Details
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- Definition Number of operating partnerships. + References No definition available. + Details
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- Definition Percentage of net profits of consolidated subsidiary allocated to preferred units. + References No definition available. + Details
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- Definition Payout period for post-termination awards. + References No definition available. + Details
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- References No definition available. + Details
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- Details
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- Details
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