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Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended
Jul. 31, 2012
Segment
Country
Jul. 31, 2011
Apr. 30, 2012
Organization And Summary Of Significant Accounting Policies [Line Items]      
Number of offices 76    
Number of countries 35    
Number of business segments 3    
Investments in affiliated companies maximum 50.00%    
Restricted cash $ 10.0   $ 10.0
Performance related bonus expenses 26.6 32.7  
Decrease in performance related bonus expenses (0.2) (1.2)  
Performance related bonus after reduction in the previous year estimate $ 26.4 $ 31.5  
Minimum
      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Intangible assets estimated useful lives 3 years    
Maximum
      
Organization And Summary Of Significant Accounting Policies [Line Items]      
Intangible assets estimated useful lives 24 years