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Stock-Based Compensation - Additional Information (Detail) - USD ($)
3 Months Ended
Jul. 31, 2016
Jul. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Option for common stock 333,000 336,000
Stock-based compensation expense $ 388,000 $ 398,000
Income tax benefit $ 145,000 146,000
Excess tax benefits from stock based compensation   $ 13,000
Stock options exercised 223,276 44,050
Total intrinsic value of options exercised $ 856,000 $ 159,000
Unrecognized compensation cost related to unvested stock option $ 3,300,000  
Weighted average period for Unrecognized compensation cost 1 year 8 months 23 days