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Compensation - Activity Associated with Limited Partnership Units Awarded to BGC Employees (Detail) - LPUs [Member] - shares shares in Thousands | 3 Months Ended | 6 Months Ended
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Jun. 30, 2020 | Jun. 30, 2019 | Jun. 30, 2020 | Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Units, Redeemed | 571 | 5,272 | 4,764 | 5,963
BGC Holdings LPUs [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Units, Redeemed | 471 | 5,101 | 4,473 | 5,621
Newmark Holdings LPUs [Member] |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |
Number of Units, Redeemed | 100 | 171 | 291 | 342

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- Definition Share-based compensation arrangement by share based payment award non option equity instrument redeemed. + References No definition available. + Details
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Namespace Prefix: | bgcp_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
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- Details
Name: | us-gaap_BusinessAcquisitionAxis=bgcp_BGCHoldingsMember
Namespace Prefix: |
Data Type: | na
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- Details
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