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Borrowing Arrangements - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
9 Months Ended
Oct. 31, 2011
Debt Disclosure [Line Items]  
Unsecured revolving credit facility $ 400.0
Unsecured revolving credit facility, option to request an increase in the amount of the credit facility up to 100.0
Line of credit facility, outstanding borrowings $ 0
Line of credit facility, expiration May 2016