Annual report pursuant to Section 13 and 15(d)

Commitments and Contingencies (Details Textual)

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Commitments and Contingencies (Details Textual) (USD $)
12 Months Ended
May 31, 2013
May 31, 2012
May 31, 2011
Jun. 21, 2013
Commitments and Contingencies (Textual) [Abstract]        
Lines of credit amount outstanding $ 0      
Credit facility, maximum borrowing capacity       500,000,000
Irrevocable standby letters of credit amount available 36,800,000 46,800,000    
Expiration date range of letters of credit July 2013 and December 2013      
Irrevocable stand by letters of credit amount outstanding 0      
Rent expense 39,900,000 43,000,000 45,400,000  
Minimum future payment obligations under purchase orders and contractual arrangements 89,100,000      
Commitments to purchase capital assets $ 9,900,000