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Net Income per Common Share - Additional Information (Detail)
3 Months Ended 6 Months Ended
Jul. 31, 2013
Jul. 31, 2012
Jul. 31, 2013
Jul. 31, 2012
Earnings Per Share [Line Items]        
Anti-dilutive common shares 100,000 4,529,300 50,000 4,352,475
Performance Stock Units
       
Earnings Per Share [Line Items]        
Anti-dilutive common shares     377,100 2,775,740