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Stock-based Compensation Expense Summary of Restricted Stock Award and Restricted Stock Unit Activity (Details) (USD $)
3 Months Ended
Apr. 30, 2012
Restricted Stock Awards And Restricted Stock Units (Member)
 
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]  
Unreleased restricted stock at January 31, 2012 2,184,100
Awarded 1,163,900
Released (263,000)
Forfeited (24,200)
Unreleased restricted stocck at April 30, 2012 3,060,800
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract]  
Unreleased restricted stock at January 31, 2012 (in usd per share) $ 36.65
Awarded (in usd per share) $ 33.32
Released (in usd per share) $ 36.05
Forfeited (in usd per share) $ 38.72
Unreleased restricted stock at April 30, 2012 (in usd per share) $ 35.42
Performance Share [Member]
 
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]  
Awarded 500,000
Unreleased restricted stocck at April 30, 2012 500,000