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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]
12 Months Ended
Apr. 30, 2017
Apr. 30, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected volatility, minimum 40.00% 40.00%
Expected volatility, maximum 43.00% 43.00%
Weighted-average volatility 0.38% 0.40%
Risk-free interest rate 0.00% 0.38%
Dividend yield 0.00% 0.00%
Minimum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years) 4 years 4 years
Maximum [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life (years) 6 years 6 months 6 years 6 months