Stock Options and Share-Based Compensation - Summary of Options Outstanding, Exercisable, and Weighted Average Exercise Prices within Exercise Price Range (Detail) (USD $)					12 Months Ended
	Apr. 30, 2014	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011	Apr. 30, 2014 Exercise Price Range Range One [Member]	Apr. 30, 2014 Exercise Price Range Range Two [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Exercise price range lower limit					$ 8.59	$ 14.69
Exercise price range upper limit					$ 12.66	$ 15.85
Options outstanding	228,250	295,550	298,050	279,800	165,650	62,600
Weighted average exercise price	$ 12.17	$ 11.84	$ 11.60	$ 11.94	$ 10.95	$ 15.40
Weighted average remaining contractual life					5 years 2 months 27 days	7 years 1 month 2 days
Aggregate intrinsic value					$ 973,000	$ 89,000
Options exercisable					87,175	26,000
Weighted average exercise price					$ 11.04	$ 14.77
Aggregate intrinsic value					$ 504,000	$ 53,000