Assumption Used to Estimate the Fair Value of Stock-Based Awards (Detail)	3 Months Ended
	Apr. 30, 2011 Year	Apr. 30, 2010 Year
Minimum | Stock Option Plans
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatilities	40.00%	40.00%
Expected lives (in years)	2.60	2.70
Risk-free interest rates	0.90%	1.30%
Maximum | Stock Option Plans
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatilities	43.00%	43.00%
Expected lives (in years)	4.4	3.7
Risk-free interest rates	1.90%	1.90%
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%
Expected forfeitures	10.50%	13.50%
ESP Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividends	0.00%	0.00%
Expected forfeitures	10.50%	13.50%
ESP Plan | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatilities	34.00%	33.00%
Expected lives (in years)	0.50	0.50
Risk-free interest rates	0.20%	0.20%
ESP Plan | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected volatilities	37.00%	45.00%
Expected lives (in years)	2.0	2.0
Risk-free interest rates	0.80%	1.10%