Annual report pursuant to Section 13 and 15(d)

Employee Benefit Plans (Details)

Employee Benefit Plans (Details) (USD $)
In Millions
12 Months Ended
May 31, 2011
May 31, 2009
May 31, 2010
Employee Benefit Plans (Textuals) [Abstract]      
Maximum salary deferral under incentive retirement plan 50% of salary    
Employer matching contribution 50% of an employee's voluntary contribution up to 4% of eligible pay for pay dates on or after January 1, 2011 100% of the first 3% of eligible pay and up to 50% of the next 2% of eligible pay, in effect prior to April 2009  
Company contributions to the Plan $ 3.5 $ 14.3  
Deferred compensation plans contribution Eligible employees can defer up to 50% of their annual base salary and bonus and outside directors can defer 100% of their Board cash compensation    
Amounts accrued under deferred compensation plans $ 8.9   $ 7.3