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Share Repurchase Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Equity, Class of Treasury Stock [Line Items]      
Total cost $ (159,226) $ (47,839) $ (475,424)
Share repurchase program      
Equity, Class of Treasury Stock [Line Items]      
Number of common shares repurchased and subsequently retired 8,092,906 1,324,700  
Total cost $ 157,044 $ 45,787  
Average cost per share, including commissions $ 19.41 $ 34.56