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Compensation - Summary of the BGC Holdings and Newmark Holdings LPUs held by BGC Employees (Detail) - LPUs [Member] - shares | Mar. 31, 2021 | Dec. 31, 2020
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Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 133,805,000 | 137,652,000
Newmark [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 12,317,000 | 13,202,000
Regular Units [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 91,507,000 |
Regular Units [Member] | Newmark [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 9,112,000 |
Preferred Units [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 42,298,000 |
Preferred Units [Member] | Newmark [Member] |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |
Number of Units, Balance outstanding | 3,205,000 |

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- Definition Number of equity instruments other than options outstanding, including both vested and non-vested instruments. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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