Quarterly report pursuant to Section 13 or 15(d)

Description of Business, Basis of Presentation, and Significant Accounting Policies (Details)

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Description of Business, Basis of Presentation, and Significant Accounting Policies (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 9 Months Ended 12 Months Ended
Feb. 28, 2014
Feb. 28, 2013
Feb. 28, 2014
Feb. 28, 2013
May 31, 2013
Description of Business, Basis of Presentation, and Significant Accounting Policies (Textual)          
Disclosure on geographic areas, Description of revenue from external customers     revenue within Germany, which represented less than one percent of the Company's total revenue revenue within Germany, which represented less than one percent of the Company's total revenue  
Disclosure on geographic areas, Long-lived assets     Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company   Long-lived assets in Germany are insignificant in relation to total long-lived assets of the Company
Maximum individual workers' compensation claims liability     $ 1.0   $ 1.0
Workers' compensation insurance costs in current liabilities 8.5   8.5   6.8
Workers' compensation insurance costs in long-term liabilities 14.8   14.8   13.7
Stock-based compensation costs recognized $ 7.1 $ 5.4 $ 21.7 $ 16.9