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Reconciliation of Weighted Average Common Shares Outstanding Used for Computation of Basic and Diluted Net Income per Common Share (Detail) - shares
3 Months Ended 9 Months Ended
Oct. 31, 2017
Oct. 31, 2016
Oct. 31, 2017
Oct. 31, 2016
Earnings Per Share [Abstract]        
Basic weighted-average common shares outstanding 109,667,224 116,829,912 113,113,597 117,087,696
Effect of dilutive options, stock appreciation rights, performance stock units and restricted stock units 433,030 563,798 318,770 365,309
Diluted weighted-average shares outstanding 110,100,254 117,393,710 113,432,367 117,453,005