Change in Accounting Method (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	6 Months Ended
	Jul. 31, 2011	Jul. 31, 2011
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decreased cost of sales and increased gross margin	$ 1.7	$ 2.3
Increase in inventory value	$ 2.3	$ 2.3