v3.26.1
CUSTOMER LIABILITIES - Schedule of customer liabilities (Details) - USD ($)
$ in Thousands
 3 Months Ended 12 Months Ended
Jun. 30, 2026
Mar. 31, 2026
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Total non-interest-bearing accounts $ 4,015,406 $ 4,581,224
Customer liabilities 7,048,800 7,103,984
Brokerage customers    
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Total non-interest-bearing accounts 3,482,453 3,998,521
Customer accounts    
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Total non-interest-bearing accounts 532,953 582,703
Term deposits    
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Term deposits $ 3,033,394 $ 2,522,760
Term deposits | Minimum    
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Debt securities, interest rate during period (in percent) 0.00% 0.04%
Term deposits | Maximum    
Segment Reporting, Entity-Wide Information Not Provided as Part of Reportable Segment, Customer, Extent of Reliance [Line Items]    
Debt securities, interest rate during period (in percent) 19.81% 19.40%