Stock Options and Share-Based Compensations - Summary of Stock Option Activity and Weighted Average Exercise Price (Detail) (USD $)	12 Months Ended
	Apr. 30, 2013	Apr. 30, 2012	Apr. 30, 2011
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted Average Exercise Price, Outstanding at beginning of year	$ 11.60	$ 11.94	$ 12.86
Weighted Average Exercise Price, Granted	$ 11.78	$ 8.90	$ 10.64
Weighted Average Exercise Price, Canceled	$ 10.57	$ 10.64	$ 11.83
Weighted Average Exercise Price, Exercised	$ 9.86	$ 9.39	$ 9.71
Weighted Average Exercise Price, Outstanding at end of year	$ 11.84	$ 11.60	$ 11.94
Weighted Average Exercise Price, Exercisable at end of year	$ 12.91	$ 13.00	$ 12.86
Number of Shares, Outstanding at beginning of year	298,050	279,800	158,925
Number of Shares, Granted	40,000	55,000	136,400
Number of Shares, Canceled	(15,750)	(22,250)	(1,675)
Number of Shares, Exercised	(26,750)	(14,500)	(13,850)
Number of Shares, Outstanding at end of year	295,550	298,050	279,800
Number of Shares, Exercisable at end of year	157,250	126,425	81,588