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Share-Based Compensation - Summarized Plan Activity (Detail) - Employee Stock Purchase Plan [Member] - shares
12 Months Ended
Jan. 31, 2019
Jan. 31, 2018
Jan. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Shares Reserved, Beginning Balance 39,207 45,224 51,600
Shares Purchased (5,354) (6,017) (6,376)
Shares Reserved, Ending Balance 33,853 39,207 45,224