Derivative Instruments and Hedging Activities - Narrative (Details) $ in Thousands	12 Months Ended
	May 31, 2023 USD ($) agreement counterparty	May 31, 2022 USD ($)	Feb. 28, 2023 USD ($)
Derivative [Line Items]
Treasury rate lock, number of agreements | agreement	3
Derivative assets, notional amount	$ 5,405,274	$ 4,791,699
Number of counterparties subject to ratings trigger and early termination provision | counterparty	1
Cash flow hedging | Designated as Hedging Instrument
Derivative [Line Items]
Notional Amount	$ 0	$ 0
Treasury lock | Cash flow hedging
Derivative [Line Items]
Derivative assets, notional amount	400,000
AOCI, cash flow hedge, cumulative gain (loss), after tax			$ 7,000
Interest rate swaps with CFC rating trigger and treasury lock
Derivative [Line Items]
Notional Amount	227,000
Payable due from CFC	26,000
Interest rate swaps and treasury lock
Derivative [Line Items]
Derivative, net liability position	$ 3,000
Interest rate swaps and treasury lock | Derivatives | Counterparty exposure risk
Derivative [Line Items]
Concentration percentage	23.00%	24.00%