Income Taxes (Components of Income Tax Expense) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2013	May 31, 2012	May 31, 2011
Current:
Federal	$ 109,964	$ 139,251	$ 70,811
State and local	12,478	17,780	15,063
Current income tax expense	122,442	157,031	85,874
Deferred	62,024	16,276	59,806
Income taxes	$ 184,466	$ 173,307	$ 145,680