Acquisitions - Summary of Acquisition Related Cost (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Acquisitions      
Acquisition-related costs $ 22,317 $ 4,346 $ 2,094
USAA AMCO      
Acquisitions      
Acquisition-related costs 21,333 3,180  
Harvest      
Acquisitions      
Acquisition-related costs 895 1,116  
RS Investments      
Acquisitions      
Acquisition-related costs     355
Other      
Acquisitions      
Acquisition-related costs $ 89 $ 50 $ 1,739