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Reconciliation of Weighted Average Shares Outstanding Used For Computation of Basic and Diluted Net Income Per Common Share (Detail)
3 Months Ended 6 Months Ended
Jul. 31, 2012
Jul. 31, 2011
Jul. 31, 2012
Jul. 31, 2011
Earnings Per Share [Line Items]        
Basic weighted average shares outstanding 144,817,752 158,581,618 144,764,072 160,436,550
Effect of dilutive options, restricted stock and performance shares 797,054 2,162,125 828,261 2,524,195
Diluted weighted average shares outstanding 145,614,806 160,743,743 145,592,333 162,960,745