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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 6 Months Ended
Jul. 31, 2018
Jul. 31, 2017
Jul. 31, 2018
Jul. 31, 2017
Earnings Per Share [Abstract]        
Basic weighted-average common shares outstanding 108,831,399 113,500,381 108,663,990 114,865,336
Effect of dilutive options, stock appreciation rights, performance stock units and restricted stock units 1,602,441 260,266 1,427,596 261,641
Diluted weighted-average shares outstanding 110,433,840 113,760,647 110,091,586 115,126,977