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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, 2017
Jul. 31, 2016
Jul. 31, 2017
Jul. 31, 2016
Earnings Per Share [Abstract]        
Basic weighted-average common shares outstanding 113,500,381 117,133,169 114,865,336 117,218,013
Effect of dilutive options, stock appreciation rights, performance stock units and restricted stock units 260,266 249,963 261,641 266,118
Diluted weighted-average shares outstanding 113,760,647 117,383,132 115,126,977 117,484,131