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Summary of Restricted Stock Unit's Activity (Detail) - Restricted Stock Units (RSUs) - $ / shares
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Non-vested awards outstanding at beginning of year, Shares 531,500    
Granted, Shares 621,500   0
Vested, Shares 0 0  
Forfeited, Shares (61,500)    
Non-vested awards outstanding at end of year, Shares 1,091,500 531,500  
Non-vested awards outstanding at beginning of year, Weighted average fair value $ 28.17    
Granted, Weighted average fair value 26.01 $ 28.10  
Vested, Weighted average fair value 0   $ 39.06
Forfeited, Weighted average fair value 27.49    
Non-vested awards outstanding at end of year, Weighted average fair value $ 26.92 $ 28.17