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           Description of Business, Basis of Presentation, and Significant Accounting Policies (Details) (USD $) 
        In Millions, unless otherwise specified  | 
        3 Months Ended | 12 Months Ended | |
|---|---|---|---|
| 
           Aug. 31, 2012 
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           Aug. 31, 2011 
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           May 31, 2012 
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| Description of business and significant accounting policies (Textual) [Abstract] | |||
| Maximum individual workers' compensation claims liability | $ 1.0 | $ 1.0 | |
| Workers' compensation insurance costs in current liabilities | 6.7 | 6.2 | |
| Workers compensation insurance costs in long-term liabilities | 14.6 | 19.0 | |
| Stock-based compensation costs recognized | $ 6.4 | $ 6.6 | |
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- Details 
          
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- Definition 
          Maximum individual claims liability workers compensation insurance. No definition available. 
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- Definition 
          Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees. Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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- Definition 
          Carrying value as of the balance sheet date of obligations and payables pertaining to claims incurred of a workers compensation nature. Used to reflect the noncurrent portion of the liabilities (due beyond one year; or beyond one operating cycle if longer). Reference 1: http://www.xbrl.org/2003/role/presentationRef 
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