Income Taxes A reconciliation of the beginning and ending amount of unrecognized tax benefits (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	May 31, 2012	May 31, 2011
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Balance at beginning of period	$ 103,099	$ 95,857
Additions for tax positions of prior years	5,660	10,529
Settlements	(5,048)	(2,194)
Change in tax regualtions	(57,182)
Statute expirations	(1,998)	(1,093)
Balance at end of period	$ 44,531	$ 103,099