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Stock-Based Compensation (Assumptions Used To Value Options) (Details) - $ / shares
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Apr. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Document Fiscal Year Focus 2017    
Expected term, years 3 years 3 years 3 years
Stock Options For Management And Director      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility, minimum 0.00% 22.95% 0.00%
Expected volatility, maximum 29.43% 24.87% 26.25%
Expected term, years 4 years 4 years 4 years
Dividend yield, minimum 0.00% 2.26% 0.00%
Dividend yield, maximum 3.94% 2.69% 2.62%
Risk-free interest rate, minimum 0.00% 1.29% 0.00%
Risk-free interest rate, maximum 1.18% 1.43% 1.43%
Weighted-average fair value $ 3.31 $ 5.28 $ 5.18
Performance Nonvested Share Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility, minimum 13.92% 12.85% 12.28%
Expected volatility, maximum 74.53% 55.27% 78.42%
Dividend yield, minimum [1] 0.00% 0.00% 0.00%
Dividend yield, maximum [1] 3.68% 2.70% 2.39%
Risk-free interest rate 0.84% 0.95% 0.81%
Weighted-average fair value $ 25.38 $ 30.00 $ 37.17
Minimum | Stock Options For Management And Director      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term, years   4 years 4 years
Maximum | Stock Options For Management And Director      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected term, years 4 years 4 years 4 years
[1] The valuation model assumes that dividends are reinvested by the Company on a continuous basis.