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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 9 Months Ended
Oct. 31, 2012
Oct. 31, 2011
Oct. 31, 2012
Oct. 31, 2011
Earnings Per Share [Line Items]        
Basic weighted average shares outstanding 145,539,816 151,170,175 145,024,545 157,313,818
Effect of dilutive options, stock appreciation rights, restricted shares and performance share units 1,547,166 2,264,636 1,067,897 2,437,675
Diluted weighted average shares outstanding 147,086,982 153,434,811 146,092,442 159,751,493