Borrowing Arrangements - Additional Information (Detail) (USD $) In Millions	6 Months Ended
	Jul. 31, 2011	Jan. 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	0
Line of credit facility, expiration	May 2016
Domestic Line of Credit
Debt Disclosure [Line Items]
Terminated line of credit facility	$ 250.0