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Stockholders' Equity - Share Based Compensation Stock Options Activity (Detail) - $ / shares
 12 Months Ended
Apr. 30, 2018
Apr. 30, 2017
Apr. 30, 2016
Shares      
Options outstanding, beginning of year, Shares 335,160 389,360 1,879,630
Exercised during the period, Shares (19,000) (54,200) (1,490,270)
Options outstanding, end of period, Shares 316,160 335,160 389,360
Weighted average remaining contractual life 3 years 1 month 28 days 4 years 3 days 5 years 14 days
Options exercisable, end of period, Shares 316,160 335,160 389,360
Weighted average remaining contractual life 3 years 1 month 28 days 4 years 3 days 5 years 14 days
Weighted-Average Exercise Price      
Options outstanding, beginning of year, Weighted-Average Exercise Price $ 6.58 $ 6.16 $ 6.37
Exercised during period, Weighted-Average Exercise Price 4.70 3.57 6.42
Options outstanding, end of period, Weighted-Average Exercise Price 6.69 6.58 6.16
Options exercisable, end of period, Weighted-Average Exercise Price $ 6.69 $ 6.58 $ 6.16