v3.21.2
REDEMPTION SETTLEMENT ASSETS, RESTRICTED - Components of redemption settlement assets (Details) - USD ($)
$ in Thousands
Sep. 30, 2021
Dec. 31, 2020
Schedule Of Redemption Settlement Assets [Line Items]    
Redemption settlement assets, Fair Value, Total $ 733,952 $ 693,461
Restricted cash    
Schedule Of Redemption Settlement Assets [Line Items]    
Redemption settlement assets, Fair Value, Total 58,196 55,427
Mutual funds    
Schedule Of Redemption Settlement Assets [Line Items]    
Redemption settlement assets, Fair Value, Total 26,220 26,850
Corporate bonds    
Schedule Of Redemption Settlement Assets [Line Items]    
Redemption settlement assets, Fair Value, Total $ 649,536 $ 611,184