Income Taxes (Reconciliation of U.S. Federal Statutory Tax Rate) (Details)	12 Months Ended
	May 31, 2023	May 31, 2022	May 31, 2021
Income Tax Disclosure [Abstract]
Federal statutory tax rate	21.00%	21.00%	21.00%
Increase/(decrease) resulting from:
State income taxes, net of federal tax benefit	4.20%	4.60%	4.30%
Tax-exempt municipal bond interest	(0.20%)	(0.20%)	(0.30%)
Stock option windfall benefit	(0.40%)	(0.90%)	(1.20%)
Tax credits	(0.70%)	(1.10%)	(0.60%)
Other items	0.10%	0.30%	0.30%
Effective income tax rate	24.00%	23.70%	23.50%