Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2016	Oct. 31, 2015	Oct. 31, 2016	Oct. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option for common stock			342,000	1,063,000
Stock-based compensation expense	$ 389,000	$ 410,000	$ 778,000	$ 808,000
Income tax benefit	145,000	$ 151,000	$ 285,000	297,000
Excess tax benefits from stock based compensation				$ 21,000
Stock options exercised			314,000	112,848
Total intrinsic value of options exercised			$ 293,000	$ 321,000
Unrecognized compensation cost related to unvested stock option	$ 3,000,000		$ 3,000,000
Weighted average period for Unrecognized compensation cost			1 year 7 months 28 days