Stock-Based Compensation - Additional Information (Detail) (USD $)	3 Months Ended		6 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option for common stock			325,000	313,000
Stock-based compensation expense	$ 390,000	$ 361,000	$ 794,000	$ 700,000
Income tax benefit	137,000	117,000	272,000	228,000
Excess tax benefits from stock based compensation			78,000	68,000
Stock option exercised			117,932	180,340
Intrinsic value of options exercised			489,000	450,000
Unrecognized compensation cost related to unvested stock option	$ 3,600,000		$ 3,600,000
Weighted average period for unrecognized compensation cost			1 year 8 months 12 days