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Investments - Equity Method Investments and Investments Carried Under Measurement Alternative (Detail) - USD ($) $ in Thousands | Dec. 31, 2020 | Dec. 31, 2019
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Schedule Of Equity Method Investments [Line Items] |  |
Equity method investments | $ 37,659 | $ 40,000
Investments carried under measurement alternative | 349 | 349
Total equity method and investments carried under measurement alternative | $ 38,008 | 40,349
Advanced Markets Holdings [Member] |  |
Schedule Of Equity Method Investments [Line Items] |  |
Investment ownership percentage amount | 43.00% |
Equity method investments | $ 8,867 | 10,259
Freedom International Brokerage [Member] |  |
Schedule Of Equity Method Investments [Line Items] |  |
Investment ownership percentage amount | 45.00% |
Equity method investments | $ 9,800 | 10,142
China Credit BGC Money Broking Company Limited [Member] |  |
Schedule Of Equity Method Investments [Line Items] |  |
Investment ownership percentage amount | 33.00% |
Equity method investments | $ 15,119 | 12,214
Other Investees [Member] |  |
Schedule Of Equity Method Investments [Line Items] |  |
Equity method investments | $ 3,873 | $ 7,385

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