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Net Income per Common Share - Additional Information (Detail) - $ / shares
3 Months Ended 6 Months Ended
Jul. 31, 2019
Jul. 31, 2018
Jul. 31, 2019
Jul. 31, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive common shares 420,000 240,000 400,000 253,750
Anti-dilutive common shares exercise price, minimum $ 28.47 $ 46.02 $ 28.47 $ 37.02
Anti-dilutive common shares exercise price, maximum $ 46.42 $ 46.42 $ 46.42 $ 46.42
Performance Stock Units (PSUs)        
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]        
Anti-dilutive common shares     780,264 1,451,382