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Stockholders' Equity (Schedule of Assumptions Used to Value Stock Options) (Details) - Stock Incentive Plan and Stock Option Grants to Employees and Directors [Member]
3 Months Ended
Jul. 31, 2017
Jul. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years) 3 years 6 months  
Expected volatility, minimum 40.00% 40.00%
Expected volatility, maximum 43.00% 43.00%
Weighted-average volatility 38.60% 40.00%
Risk-free interest rate 0.38% 0.38%
Dividend yield 0.00% 0.00%
Expected forfeiture rate
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years)   4 years
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years)   6 years 6 months