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Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 6 Months Ended
Oct. 31, 2012
Country
Jul. 31, 2012
Oct. 31, 2011
Jul. 31, 2011
Oct. 31, 2012
Segment
Country
Oct. 31, 2011
Apr. 30, 2012
Organization And Summary Of Significant Accounting Policies [Line Items]              
Number of offices 76       76    
Number of countries 35       35    
Number of business segments         3    
Investments in affiliated companies maximum 50.00%       50.00%    
Restricted cash $ 10.0       $ 10.0   $ 10.0
Performance related bonus expenses 27.4   28.2   54.0 60.9  
Decrease in performance related bonus expenses   (0.2)   (1.2) (0.2) (1.2)  
Performance related bonus after reduction in the previous year estimate         $ 53.8 $ 59.7  
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