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Summary of Other Information Related to Stock Options (Detail) - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Jan. 31, 2018
Jan. 31, 2017
Jan. 31, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Net cash proceeds from the exercise of stock options   $ 4,096 $ 46,400
Stock Options      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Weighted-average grant date fair value—per share $ 5.37 $ 7.31 $ 7.46
Intrinsic value of awards exercised   $ 1,566 $ 14,193
Net cash proceeds from the exercise of stock options   $ 4,096 $ 46,400