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Share Based Compensation Stock Options Activity (Detail) - $ / shares
 9 Months Ended
Jan. 31, 2016
Jan. 31, 2015
Number of shares and weighted average exercise prices    
Options outstanding, beginning of year, Shares 1,879,630 2,258,349
Exercised during the period, Shares (707,179) (222,884)
Canceled/forfeited during period, Shares   (13,000)
Options outstanding, end of period, Shares 1,172,451 2,022,465
Weighted average remaining contractual life 5 years 26 days 5 years 3 months 11 days
Options exercisable, end of period, Shares 1,172,457 1,943,800
Weighted average remaining contractual life 5 years 26 days 5 years 2 months 12 days
Weighted-Average Exercise Price    
Options outstanding, beginning of year, Weighted-Average Exercise Price $ 6.37 $ 6.15
Exercised during period, Weighted-Average Exercise Price 8.26 4.62
Canceled/forfeited during period, Weighted-Average Exercise Price   7.98
Options outstanding, end of period, Weighted-Average Exercise Price 5.23 6.31
Options exercisable, end of period, Weighted-Average Exercise Price $ 5.23 $ 6.23