Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2018	Jan. 31, 2017
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option to purchase common stock			1,196,000	342,000
Stock-based compensation expense	$ 314,000	$ 333,000	$ 1,108,000	$ 1,111,000
Income tax benefit	138,000	$ 124,000	$ 413,000	$ 409,000
Stock options exercised			778,129	593,082
Total intrinsic value of options exercised			$ 2,200,000	$ 1,900,000
Unrecognized compensation cost related to unvested stock option	$ 3,600,000		$ 3,600,000
Weighted average period for Unrecognized compensation cost			1 year 10 months 6 days