Stock-Based Compensation - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Jan. 31, 2019	Jan. 31, 2018	Jan. 31, 2019	Jan. 31, 2018
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option to purchase common stock			1,201,000	1,196,000
Stock-based compensation expense	$ 466	$ 314	$ 1,308	$ 1,108
Income tax excess benefit	26	$ 25	$ 260	$ 51
Stock options exercised			456,113	778,129
Total intrinsic value of options exercised			$ 2,100	$ 2,200
Unrecognized compensation cost related to unvested stock option	$ 5,000		$ 5,000
Weighted average period for unrecognized compensation cost			1 year 11 months 8 days