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Shareholders' Equity and Share-Based Compensation - Assumptions used in Black-Scholes Model (Details) - $ / shares
12 Months Ended
Apr. 28, 2018
Apr. 29, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value of options granted $ 2.82 $ 2.93 $ 2.92
Risk-free interest rate 1.95%    
Expected dividend rate 3.27% 3.15% 2.78%
Expected volatility 42.51%    
Expected life of option 6 years 10 months    
Minimum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate   1.31% 1.70%
Expected volatility   44.12% 42.71%
Expected life of option   5 years 9 months 11 days 5 years 9 months 11 days
Maximum      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate   1.44% 1.90%
Expected volatility   44.51% 48.32%
Expected life of option   6 years 11 months 23 days 6 years 11 months 23 days