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Net Income per Common Share - Additional Information (Detail) - $ / shares
3 Months Ended
Apr. 30, 2019
Apr. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive common shares 380,000 267,500
Anti-dilutive common shares exercise price, minimum $ 35.85 $ 37.02
Anti-dilutive common shares exercise price, maximum $ 46.42 $ 46.02
Performance Stock Units (PSUs)    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Anti-dilutive common shares 711,418 1,713,773