| 
           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 | 
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- Details 
          
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- Definition 
          Expiry date range of letters of credit. No definition available. 
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- Definition 
          Irrevocable standby letters of credit amount available. No definition available. 
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- Definition 
          Amount of contractual obligation, including but not limited to, long-term debt, capital lease obligations, operating lease obligations, purchase obligations, and other commitments. No definition available. 
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- Definition 
          The total amount of the contingent obligation under letters of credit outstanding as of the reporting date. No definition available. 
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- Definition 
          Amount borrowed under the credit facility as of the balance sheet date. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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