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Share Repurchase Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
3 Months Ended 6 Months Ended
Jul. 31, 2015
Jul. 31, 2016
Jul. 31, 2015
Equity, Class of Treasury Stock [Line Items]      
Number of common shares repurchased and subsequently retired 6,635,164 324,700 7,037,141
Total cost $ 236,312 $ 10,704 $ 253,618
Average cost per share, including commissions $ 35.62 $ 32.97 $ 36.04