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Net Income Per Common Share (Narrative) (Details) (USD $)
3 Months Ended 6 Months Ended
Jul. 31, 2011
Jul. 31, 2010
Jul. 31, 2011
Jul. 31, 2010
Net Income Per Common Share        
Anti-dilutive common shares 4,448,250 1,250,650 2,890,900 1,091,400
Anti-dilutive common shares exercise price, minimum $ 30.93 $ 37.35 $ 30.93 $ 37.35
Anti-dilutive common shares exercise price, maximum $ 39.58 $ 39.58 $ 39.58 $ 39.58