Annual report pursuant to Section 13 and 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 $)
 12 Months Ended
May 31, 2013
May 31, 2012
May 31, 2011
Accounting Policies [Abstract]      
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 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  
Period in which payroll taxes typically remitted after receipt of collections from client one to 30 days    
Maximum period payroll taxes remitted after receipt of collections from client 90 days    
Allowance for doubtful accounts $ 1,000,000 $ 1,200,000  
Direct costs billed and incurred 3,000,000,000 3,300,000,000 3,900,000,000
Maximum individual workers' compensation claims liability 1,000,000 1,000,000  
Workers' compensation insurance costs in current liabilities 6,800,000 6,200,000  
Workers' compensation insurance costs in long-term liabilities 13,700,000 19,000,000  
Reserve for uncertain tax positions $ 19,800,000 $ 36,800,000  
Minimum [Member]
      
Property, Plant and Equipment [Line Items]      
Finite-Lived Intangible Asset, Useful Life 5 years    
Maximum [Member]
      
Property, Plant and Equipment [Line Items]      
Finite-Lived Intangible Asset, Useful Life 12 years    
Building and Building Improvements [Member] | Minimum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 10 years    
Building and Building Improvements [Member] | Maximum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 35 years    
Data Processing Equipment [Member] | Minimum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 2 years    
Data Processing Equipment [Member] | Maximum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 7 years    
Furniture Fixtures And Equipment [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 7 years    
Leasehold Improvements [Member] | Maximum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 10 years    
Software Development [Member] | Minimum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 3 years    
Software Development [Member] | Maximum [Member]
      
Property, Plant and Equipment [Line Items]      
Property, Plant and Equipment, Useful Life 15 years