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Schedule I - Parent Company Only - Organization and Basis of Presentation - Additional Information (Detail) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2019 | Dec. 31, 2018 | Dec. 31, 2017
Description Of Business [Line Items] |  |  |
Dividends declared per share to BGC Class A and Class B common stockholders | $ 0.56 | $ 0.72 | $ 0.70
Dividends paid per share to BGC Class A and Class B common stockholders | 0.56 | 0.72 | 0.70
Parent Company [Member] |  |  |
Description Of Business [Line Items] |  |  |
Dividends declared per share to BGC Class A and Class B common stockholders | 0.56 | 0.72 | 0.70
Dividends paid per share to BGC Class A and Class B common stockholders | $ 0.56 | $ 0.72 | $ 0.70

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