Deferred Compensation - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	Oct. 31, 2011	Jan. 31, 2011
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 430.9
Deferred compensation liability	32.7	31.3
Deferred compensation liability current	3.2	3.4
Deferred compensation liability non-current	29.5	27.9
Rabbi Trust
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Marketable securities	$ 32.7	$ 31.3