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Principal Amount, Unamortized Debt Discount, Net Carrying Amount of the Liability Component, and Carrying Amount of Equity Component of 6.25% Debentures, Issued 2006 (Detail) (USD $)
In Thousands, unless otherwise specified
Jan. 31, 2012
Jan. 31, 2011
Debt Instrument [Line Items]    
Principal amount $ 254,349  
Net carrying amount of the liability component 214,573 209,348
6.25% Debentures due 2026, issued 2006
   
Debt Instrument [Line Items]    
Principal amount   165,000
Unamortized debt discount   (7,157)
Net carrying amount of the liability component   157,843
Equity component   $ 21,766