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Summary of Restricted Stock Award and Restricted Stock Unit Activity (Detail) (Restricted Stock Awards and Restricted Stock Units, USD $)
12 Months Ended
Jan. 31, 2012
Restricted Stock Awards and Restricted Stock Units
 
Unreleased restricted stock  
Unreleased restricted stock at January 31, 2011 1,426,800
Granted 1,610,500
Released (707,600)
Canceled (145,600)
Unreleased restricted stock at January 31, 2012 2,184,100
Weighted average grant date fair value  
Unreleased restricted stock at January 31, 2011 $ 30.43
Granted $ 37.07
Released $ 25.95
Forfeited $ 32.37
Unreleased restricted stock at January 31, 2012 $ 36.65