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Compensation - Activity Associated with LPU Awarded to BGC Employees (Detail) - LPUs [Member] - shares | 12 Months Ended
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Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Number of Units, Balance outstanding at beginning of period | 79,729,000 | 58,323,000 | 50,835,000
Number of Units, Granted | 47,916,000 | 36,821,000 | 20,309,000
Number of Units, Redeemed/exchanged units | (21,110,000) | (14,908,000) | (7,283,000)
Number of Units, Forfeited units | (4,128,000) | (507,000) | (5,538,000)
Number of Units, Balance outstanding at end of period | 102,407,000 | 79,729,000 | 58,323,000
Newmark Units [Member] |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Number of Units, Balance outstanding at beginning of period | 22,113,000 | 26,510,000 |
Number of Units, Granted | 662,000 | 2,694,000 | 26,510,000
Number of Units, Redeemed/exchanged units | (1,024,000) | (7,032,000) |
Number of Units, Forfeited units | (7,144,000) | (59,000) |
Number of Units, Balance outstanding at end of period | 14,607,000 | 22,113,000 | 26,510,000

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- Definition Number of exchangeable limited partnership units redeemed or exchanged into the Company's class A common stock during the period. + References No definition available. + Details
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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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- Definition Number of shares under non-option equity instrument agreements that were cancelled as a result of occurrence of a terminating event. + 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)(iv)(3) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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- Definition Net number of non-option equity instruments granted to participants. + 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)(iv)(1) -URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901 + Details
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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=116856206&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=116856206&loc=d3e5070-113901 + Details
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- Details
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- Details
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