Quarterly report pursuant to Section 13 or 15(d)

Basic and Diluted Earnings per Common Share Attributable to Common Stockholders (Detail)

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Basic and Diluted Earnings per Common Share Attributable to Common Stockholders (Detail) - USD ($)
$ / shares in Units, shares in Thousands, $ in Thousands
3 Months Ended
Jul. 31, 2015
Jul. 31, 2014
Earnings Per Share Disclosure [Line Items]    
Net income $ 23,082 $ 14,533
Less: distributed and undistributed earnings to nonvested restricted stockholders 224  
Basic net earnings attributable to common stockholders 22,858 14,533
Add: undistributed earnings to nonvested restricted stockholders 176  
Less: reallocation of undistributed earnings to nonvested restricted stockholders 174  
Diluted net earnings attributable to common stockholders $ 22,860 $ 14,533
Basic weighted-average number of common shares outstanding 49,493 48,703
Diluted weighted-average number of common shares outstanding 50,014 49,591
Basic earnings per share $ 0.46 $ 0.30
Diluted earnings per share $ 0.46 $ 0.29
ESPP    
Earnings Per Share Disclosure [Line Items]    
Stock 3  
Restricted Stock    
Earnings Per Share Disclosure [Line Items]    
Stock 452 756
Stock Options    
Earnings Per Share Disclosure [Line Items]    
Stock 66 132