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, 2015
May. 31, 2014
May. 31, 2013
Commitments and Contingencies (Textual) [Abstract]      
Rent expense $ 39,400,000 $ 39,100,000 $ 39,900,000
Minimum future payment obligations under purchase orders and contractual arrangements 104,800,000    
Commitments to purchase capital assets 9,500,000    
Line of Credit [Member]      
Line of Credit Facility [Line Items]      
Amount outstanding 0    
Standby Letters of Credit [Member]      
Line of Credit Facility [Line Items]      
Amount available $ 43,000,000 43,000,000  
Expiration date range of letters of credit July 2015 and April 2016    
Irrevocable stand by letters of credit amount outstanding $ 0    
Revolving Credit Facility [Member]      
Line of Credit Facility [Line Items]      
Amount outstanding $ 0    
Line of credit facility, initial term 5 years    
Expiration date Jun. 21, 2018    
Maximum borrowing capacity $ 750,000,000 $ 500,000,000