Quarterly report [Sections 13 or 15(d)]

INVESTMENT SECURITIES - Narrative (Details)

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INVESTMENT SECURITIES - Narrative (Details)
$ in Thousands
6 Months Ended 12 Months Ended
Sep. 30, 2025
USD ($)
Mar. 31, 2025
USD ($)
issuer
Defined Benefit Plan Disclosure [Line Items]    
Investment securities $ 2,511,419 $ 2,814,733
Number of issuers | issuer   2
Accumulated impairment loss 388 $ 406
Fair value of held-to-maturity 311,215 64,952
Non-US sovereign debt    
Defined Benefit Plan Disclosure [Line Items]    
Accumulated impairment loss 388 378
Fair value of held-to-maturity 311,215 64,952
Quoted Prices in Active Markets for Identical Assets | Non-US sovereign debt    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of held-to-maturity 70,876 45,216
Significant Other Observable Inputs | Non-US sovereign debt    
Defined Benefit Plan Disclosure [Line Items]    
Fair value of held-to-maturity $ 240,339 $ 19,736
Kazakhstan Sustainability Fund JSC    
Defined Benefit Plan Disclosure [Line Items]    
Percentage of trading securities 10.00% 10.00%
Investment securities   $ 578,862
Ministry of Finance of the Republic of Kazakhstan    
Defined Benefit Plan Disclosure [Line Items]    
Percentage of trading securities 10.00% 10.00%
Investment securities $ 1,492,464 $ 1,527,340