Quarterly report [Sections 13 or 15(d)]

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details)

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SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES - Narrative (Details) - USD ($)
$ in Thousands
3 Months Ended 6 Months Ended
Sep. 30, 2025
Sep. 30, 2024
Sep. 30, 2025
Sep. 30, 2024
Apr. 30, 2025
Mar. 31, 2025
Revenue, Major Customer [Line Items]            
Fee and commission income $ 132,238 $ 121,051 $ 239,880 $ 236,540    
Interest income on margin loans to customers 72,814 40,917 133,103 91,984    
Goodwill 46,247 53,166 46,247 53,166   $ 49,093
Astel            
Revenue, Major Customer [Line Items]            
Goodwill         $ 1,740  
Percentage of voting interests acquired         100.00%  
Single non-related party | Revenue benchmark | Customer concentration risk            
Revenue, Major Customer [Line Items]            
Fee and commission income 97,214 71,410 169,539 136,289    
Interest income on margin loans to customers $ 4,545 $ 7,601 $ 13,492 $ 26,995