Income Taxes (Reconciliation of Income Tax Expense Using the Statutory Rate and Actual Income Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2014	May 31, 2013	May 31, 2012
Reconciliation of income tax expense using the statutory rate and actual income tax expense is as follows:
Income taxes at the U.S. federal statutory rate	$ 212,750	$ 174,968	$ 164,830
State and local income taxes, net of federal benefit	20,279	12,192	11,876
Other	387	(2,694)	(3,399)
Income taxes	$ 233,416	$ 184,466	$ 173,307