Summary of Changes in Outstanding Options (Detail) - USD ($)	12 Months Ended
	Apr. 30, 2015	Apr. 30, 2014	Apr. 30, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Outstanding at May 1, 2014	2,894,072
Number of Shares Granted	349,000
Number of Shares Exercised	(490,912)	(890,341)	(386,356)
Number of Shares Forfeited/cancelled	(31,091)
Number of Shares Outstanding at April 30, 2015	2,721,069	2,894,072
Number of Shares Exercisable at April 30, 2015	1,203,369
Weighted Average Exercise Price Outstanding at May 1, 2014	$ 7.59
Weighted Average Exercise Price Granted	9.61
Weighted Average Exercise Price Exercised	5.55
Weighted Average Exercise Price Forfeited/cancelled	7.70
Weighted Average Exercise Price Outstanding at April 30, 2015	8.21	$ 7.59
Weighted Average Exercise Price Exercisable at April 30, 2015	$ 7.62
Weighted Average Remaining Contractual Term Outstanding at April 30, 2015	3 years 3 months 18 days
Weighted Average Remaining Contractual Term Exercisable at April 30, 2015	2 years 6 months
Aggregate Intrinsic Value Outstanding at April 30, 2015	$ 4,103,941
Aggregate Intrinsic Value Exercisable at April 30, 2015	$ 2,526,142