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Stock-based Compensation Expense Summary of Restricted Stock Award and Restricted Stock Unit Activity (Details) (USD $)
6 Months Ended 3 Months Ended
Jul. 31, 2012
Performance Shares [Member]
Jul. 31, 2012
Restricted Stock [Member]
Jan. 31, 2012
Restricted Stock [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 500,000 3,184,300  
Released   (305,800)  
Forfeited   (65,200)  
Unreleased restricted stocck at April 30, 2012 500,000 4,997,400 2,184,100
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)   $ 32.89  
Released (in usd per share)   $ 35.46  
Forfeited (in usd per share)   $ 37.42  
Unreleased restricted stock at April 30, 2012 (in usd per share)   $ 34.32 $ 36.65