Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2018	Oct. 31, 2017	Oct. 31, 2018	Oct. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option to purchase common stock			1,189,000	884,000
Stock-based compensation expense	$ 443,000	$ 477,000	$ 841,000	$ 793,000
Income tax excess benefit	12,000	$ (47,000)	$ 286,000	$ 80,000
Stock options exercised			343,000	482,000
Total intrinsic value of options exercised			$ 1,900,000	$ 1,300,000
Unrecognized compensation cost related to unvested stock option	$ 5,400,000		$ 5,400,000
Weighted average period for Unrecognized compensation cost			2 years 14 days