Quarterly report pursuant to Section 13 or 15(d)

Commitments and Contingencies (Details Textual)

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Commitments and Contingencies (Details Textual) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Aug. 31, 2012
May 31, 2012
Commitments and Contingencies (Textual) [Abstract]    
Lines of credit amount outstanding $ 0  
Irrevocable standby letters of credit amount available 38.8 46.8
Irrevocable stand by letters of credit amount outstanding 0  
Expiration date range of letters of credit December 2012 and July 2013  
Commitments to purchase capital assets $ 19.3 $ 7.6