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Stock-Based Compensation (Assumptions Used To Value Options) (Details) - $ / shares
12 Months Ended
Apr. 30, 2016
Apr. 30, 2015
Apr. 30, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Document Fiscal Year Focus 2016    
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 22.95% 0.00% 30.89%
Expected volatility, maximum 24.87% 26.25% 31.57%
Expected term, years 4 years 4 years 4 years
Dividend yield, minimum 2.26% 0.00% 2.77%
Dividend yield, maximum 2.69% 2.62% 2.87%
Risk-free interest rate, minimum 1.29% 0.00% 1.06%
Risk-free interest rate, maximum 1.43% 1.43% 1.31%
Weighted-average fair value $ 5.28 $ 5.18 $ 5.57
Performance Nonvested Share Units      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility, minimum 12.85% 12.28% 11.75%
Expected volatility, maximum 55.27% 78.42% 70.17%
Dividend yield, minimum [1] 0.00% 0.00% 0.00%
Dividend yield, maximum [1] 2.70% 2.39% 2.88%
Risk-free interest rate 0.95% 0.81% 0.61%
Weighted-average fair value $ 30.00 $ 37.17 $ 28.59
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.