Acquisitions - Summary of Rollforward of Restructuring and Integration Liabilities (Details) - USD ($)
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Rollforward of restructuring and integration liabilities      
Liability balance, beginning of year $ 100,000 $ 100,000 $ 7,400,000
Integration costs 2,300,000   400,000
Restructuring and integration costs 8,678,000 742,000 6,205,000
Settlement of liabilities (5,800,000) (700,000) (13,500,000)
Liability balance, end of year 3,000,000 100,000 100,000
Accrued expenses      
Rollforward of restructuring and integration liabilities      
Liability balance, beginning of year 100,000 100,000  
Liability balance, end of year 2,900,000 100,000 100,000
Other liabilities      
Rollforward of restructuring and integration liabilities      
Liability balance, end of year 100,000    
USAA AMCO      
Rollforward of restructuring and integration liabilities      
Integration costs 8,700,000 0 0
Severance expense      
Rollforward of restructuring and integration liabilities      
Severance expense   $ 700,000 300,000
Severance expense | USAA AMCO      
Rollforward of restructuring and integration liabilities      
Severance expense 6,200,000    
Severance expense | RS Investments      
Rollforward of restructuring and integration liabilities      
Severance expense     500,000
Contract termination expense | USAA AMCO      
Rollforward of restructuring and integration liabilities      
Severance expense $ 200,000    
Contract termination expense | RS Investments      
Rollforward of restructuring and integration liabilities      
Severance expense     $ 5,000,000