Stockholders' Equity - Share Based Compensation Stock Options Activity (Detail) - $ / shares	12 Months Ended
	Apr. 30, 2017	Apr. 30, 2016	Apr. 30, 2015
Shares
Options outstanding, beginning of year, Shares	389,360	1,879,630	2,258,349
Exercised during the period, Shares	(54,200)	(1,490,270)	(365,719)
Canceled/forfeited during period, Shares			(13,000)
Options outstanding, end of year, Shares	335,160	389,360	1,879,630
Weighted average remaining contractual life	4 years 4 days	5 years 15 days	5 years 7 days
Options exercisable, end of year, Shares	335,160	389,360	1,878,464
Weighted average remaining contractual life	4 years 4 days	5 years 15 days	5 years 7 days
Weighted-Average Exercise Price
Options outstanding, beginning of year, Weighted-Average Exercise Price	$ 6.16	$ 6.37	$ 6.15
Exercised during period, Weighted-Average Exercise Price	3.57	6.42	4.96
Canceled/forfeited during period, Weighted-Average Exercise Price			7.98
Options outstanding, end of year, Weighted-Average Exercise Price	6.58	6.16	6.37
Options exercisable, end of year, Weighted-Average Exercise Price	$ 6.58	$ 6.16	$ 6.36