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Condensed Consolidated Statements of Changes in Equity (Parenthetical) - shares
3 Months Ended 6 Months Ended
Jun. 30, 2019
Jun. 30, 2019
Jun. 30, 2018
Class A Common Stock [Member]      
Equity-based compensation and related issuance, shares     327,746
Grant of exchangeability, redemption and issuance of limited partnership interests and issuance of common stock, shares 949,283 1,447,412  
Repurchase of shares 1,613,032 1,613,032  
Issuance of common stock, shares 28,484 36,935  
Noncontrolling Interests in Subsidiaries [Member]      
BGC's purchase of exchangeable limited partnership units in Newmark Holdings, shares     16,606,726