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Stock-Based Compensation (Assumptions Used To Value Options) (Details) - $ / shares
12 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Document Fiscal Year Focus 2018    
Performance-Based Nonvested Share Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility, minimum 13.33% 13.92% 12.85%
Expected volatility, maximum 81.19% 74.53% 55.27%
Expected term, years 3 years 3 years 3 years
Risk-free interest rate   0.84% 0.95%
Dividend yield, minimum [1] 0.00% 0.00% 0.00%
Dividend yield, maximum [1] 3.23% 3.68% 2.70%
Risk-free interest rate, minimum 1.42%    
Risk-free interest rate, maximum 1.55%    
Weighted-average fair value $ 32.66 $ 25.38 $ 30.00
[1] The valuation model assumes that dividends are reinvested by the Company on a continuous basis.