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Restructuring Charges Net - Additional Information (Detail) (USD $)
3 Months Ended 6 Months Ended
Oct. 31, 2012
Oct. 31, 2012
Apr. 30, 2012
Restructuring Cost and Reserve [Line Items]      
Restructuring charges $ 15,495,000 $ 15,495,000  
Restructuring liability included in other long-term liabilities 3,400,000 3,400,000 1,400,000
Long-term restructuring liability, payment term (in years) 14 years 14 years  
Severance
     
Restructuring Cost and Reserve [Line Items]      
Restructuring charges 11,300,000 11,300,000  
Facilities
     
Restructuring Cost and Reserve [Line Items]      
Restructuring charges $ 4,200,000 $ 4,200,000