Acquisition - USAA Acquisition (Details) - USD ($)
$ in Thousands
Jul. 01, 2019
Sep. 30, 2019
Jun. 30, 2019
Dec. 31, 2018
Acquisitions        
Contingent consideration liability   $ 102,800   $ 716
Restricted Cash     $ 71,900  
Credit Agreement | Adjusted London Interbank Offered Rate (LIBOR)        
Acquisitions        
Base Spread (as a percent) 3.25%      
Credit Agreement | Base Rate        
Acquisitions        
Base Spread (as a percent) 2.25%      
Credit Agreement | London Interbank Offered Rate (LIBOR)        
Acquisitions        
Base Spread (as a percent) 3.25%      
Revolving Credit Facility        
Acquisitions        
Maximum borrowing capacity $ 100,000      
Debt Instrument, Term 5 years      
Letter of Credit        
Acquisitions        
Maximum borrowing capacity $ 10,000      
Term Loans        
Acquisitions        
Principal amount $ 1,100,000      
Debt Instrument, Term 7 years      
USAA AMCO        
Acquisitions        
Percentage of outstanding common stock acquired 100.00%      
Total consideration $ 954,100      
Payments to acquire business 851,300      
Payments to acquire business, restricted cash 71,900      
Contingent consideration liability 102,800 $ 102,800    
Maximum aggregate contingent payment 150,000      
Maximum annual contingent payment $ 37,500      
Period of time over which contingent payments will be made 4 years      
Contingent consideration threshold percentage 80.00%      
Annual revenue percentage requirement to achieve the maximum contingent payment 100.00%      
Post-closing adjustment period 1 year