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Notes Payable - Principal Amount, Unamortized Debt Discount, Net Carrying Amount of the Liability Component, and Carrying Amount of the Equity Component of the 4.00% Debentures (Detail) (USD $)
In Thousands, unless otherwise specified
Jul. 31, 2012
Jan. 31, 2012
Debt Instrument [Line Items]    
Net carrying amount of the liability component $ 217,206 $ 214,573
4.00% Debentures due 2031
   
Debt Instrument [Line Items]    
Principal amount 253,000 253,000
Unamortized debt discount (37,163) (39,776)
Net carrying amount of the liability component 215,837 213,224
Equity component $ 43,930 $ 43,930