Investment Securities - Equity Securities (Details) - USD ($) $ in Thousands	Aug. 31, 2023	May 31, 2023
Debt and Equity Securities, FV-NI [Line Items]
Total equity securities, at fair value	$ 36,780	$ 35,494
Farmer Mac—Series C non-cumulative preferred stock | Series C Preferred Stock
Debt and Equity Securities, FV-NI [Line Items]
Total equity securities, at fair value	25,200	25,750
Farmer Mac—Class A common stock
Debt and Equity Securities, FV-NI [Line Items]
Total equity securities, at fair value	$ 11,580	$ 9,744