Investment Securities - Schedule of composition of investments in debt securities (Details) - USD ($) $ in Thousands	May 31, 2026	May 31, 2025
Debt and Equity Securities, FV-NI [Line Items]
Total debt securities trading, at fair value	$ 31,144	$ 113,663
Corporate debt securities
Debt and Equity Securities, FV-NI [Line Items]
Total debt securities trading, at fair value	30,765	107,957
Commercial agency MBS
Debt and Equity Securities, FV-NI [Line Items]
Total debt securities trading, at fair value	379	525
U.S. state and municipality debt securities
Debt and Equity Securities, FV-NI [Line Items]
Total debt securities trading, at fair value	0	1,049
Other ABS
Debt and Equity Securities, FV-NI [Line Items]
Total debt securities trading, at fair value	$ 0	$ 4,132