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Share Based Compensation Stock Options Activity (Detail) - $ / shares
 3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
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 (132,599) (99,554)
Options outstanding, end of period, Shares 1,747,031 2,158,795
Weighted average remaining contractual life 5 years 15 days 5 years 9 months 26 days
Options exercisable, end of period, Shares 1,745,865 1,892,631
Weighted average remaining contractual life 5 years 15 days 5 years 7 months 6 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 4.78 4.25
Options outstanding, end of period, Weighted-Average Exercise Price 6.49 6.24
Options exercisable, end of period, Weighted-Average Exercise Price $ 6.48 $ 6.23