Compensation - Grant of Conversion Rights to Newmark Employees (Details) - Limited Partnership Units - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Mar. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award
Notional value		$ 206,851	$ 194,995
Estimated fair value of limited partnership units	$ 182,800	$ 199,149

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