Assumption Used to Estimate the Fair Value of Stock-Based Awards (Detail)	12 Months Ended
	Jan. 31, 2012	Jan. 31, 2011	Jan. 31, 2010
Stock Option Plans
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividends	0.00%	0.00%	0.00%
ESP Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividends	0.00%	0.00%	0.00%
Employee Qualified Stock Purchase Plan 1998 ESP Plan | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	34.00%	33.00%	43.00%
Range of expected lives (in years)	0.5	0.5	0.5
Range of risk-free interest rates	0.10%	0.20%	0.20%
Expected forfeitures	7.80%	10.50%	13.50%
Employee Qualified Stock Purchase Plan 1998 ESP Plan | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	44.00%	47.00%	73.00%
Range of expected lives (in years)	2	2	2
Range of risk-free interest rates	0.80%	1.10%	1.00%
Expected forfeitures	10.50%	13.50%
Employee Stock Option Member | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	40.00%	40.00%	43.00%
Range of expected lives (in years)	2.6	2.6	2.7
Range of risk-free interest rates	0.50%	0.80%	1.00%
Expected forfeitures	7.80%	10.50%	13.50%
Employee Stock Option Member | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	49.00%	45.00%	55.00%
Range of expected lives (in years)	4.8	4.4	4
Range of risk-free interest rates	1.90%	1.90%	2.40%
Expected forfeitures	10.50%	13.50%