Share Based Compensation Stock Options Activity (Detail) (USD $)	6 Months Ended
	Oct. 31, 2013	Oct. 31, 2012
Number of shares and weighted average exercise prices
Options outstanding, beginning of year, Shares	3,019,127	3,988,164
Granted during year		3,500
Exercised during year, Shares	(418,466)	(834,508)
Canceled/forfeited during year, Shares	(28,000)	(105,496)
Options outstanding, end of year, Shares	2,572,661	3,051,660
Weighted average remaining contractual life	6 years 2 months 19 days	6 years 7 months 21 days
Options exercisable, end of period, Shares	2,013,974	1,890,540
Weighted average remaining contractual life	5 years 8 months 23 days	5 years 4 months 2 days
Weighted-Average Exercise Price
Options outstanding, beginning of year, Weighted-Average Exercise Price	$ 5.31	$ 4.67
Granted during year, Weighted-Average Exercise Price		$ 11.02
Exercised during year, Weighted-Average Exercise Price	$ 2.55	$ 4.10
Canceled/forfeited during year, Weighted-Average Exercise Price	$ 5.59	$ 3.91
Options outstanding, end of year, Weighted-Average Exercise Price	$ 5.76	$ 4.86
Options exercisable, end of period, Weighted-Average Exercise Price	$ 5.79	$ 5.10