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Stock-Based Compensation Fair Value (Details) - Stock options - $ / shares
12 Months Ended
Apr. 30, 2016
Apr. 30, 2015
Weighted average assumptions used to estimate fair value of stock options granted    
Expected term (in years) 6 years 6 years
Expected volatility (as a percent) 36.14% 44.65%
Risk-free interest rate (as a percent) 1.88% 1.92%
Weighted average fair value at grant date (in dollars per share) $ 10.18 $ 14.05