Stock-Based Compensation - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2017	Jan. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Option for common stock			342,000	1,076,200
Stock-based compensation expense	$ 333,000	$ 404,000	$ 1,111,000	$ 1,212,000
Income tax benefit	124,000	$ 148,000	$ 409,000	443,000
Excess tax benefits from stock based compensation				$ 231,000
Stock options exercised			593,082	276,700
Total intrinsic value of options exercised			$ 786,000	$ 1,100,000
Unrecognized compensation cost related to unvested stock option	$ 2,700,000		$ 2,700,000
Weighted average period for Unrecognized compensation cost			1 year 7 months 2 days