Summary of Shares Issued Under the ESPPs (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Employee Stock Purchase Plan [Line Items]
Shares issued under the ESPPs	2,099	3,461	4,143
Cash received for the purchase of shares under the ESPPs	$ 22,155	$ 19,019	$ 18,237
Weighted average purchase price per share	$ 10.55	$ 5.50	$ 4.40