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Stock-Based Compensation (Narrative) (Details) (USD $)
Share data in Millions, unless otherwise specified
12 Months Ended
Apr. 30, 2011
Apr. 30, 2010
Apr. 30, 2009
Stock-based compensation expenses, gross $ 14,500,000 $ 29,400,000 $ 32,600,000
Tax effect of stock-based compensation 5,400,000 10,500,000 12,200,000
Stock-based compensation 14,500,000 29,369,000 26,557,000
Excess tax benefit from share-based compensation, financing activities 500,000 1,600,000 8,600,000
Realized tax benefits 4,400,000 6,600,000 20,200,000
Shares reserved for future awards under stock-based compensation plans 11.5    
Purchase price discount 90.00%    
Discount from market price 10.00%    
Stock Options [Member]
     
Intrinsic value of options exercised 1,800,000 5,400,000 33,000,000
Unrecognized compensation costs 3,200,000    
Weighted-average period of recognition (years) 2    
Nonvested Shares and Performance Nonvested [Member]
     
Fair value of shares vesting during period 13,000,000 15,500,000 21,100,000
Unrecognized compensation costs $ 11,500,000    
Weighted-average period of recognition (years) 2