Stock-based Compensation Expense Assumption Used to Estimate the Fair Value of Stock-Based Awards (Details)	3 Months Ended		9 Months Ended
	Oct. 31, 2014	Oct. 31, 2013	Oct. 31, 2014	Oct. 31, 2013
ESP Plan
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Expected dividends	0.00%		0.00%
ESP Plan | Minimum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	29.00%	30.00%	29.00%	27.00%
Range of expected lives (in years)	6 months	6 months	6 months	6 months
Expected dividends	0.00%	0.00%
Range of risk-free interest rates	0.00%	0.10%	0.00%	0.10%
ESP Plan | Maximum
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities	30.00%	35.00%	33.00%	36.00%
Range of expected lives (in years)	2 years	2 years	2 years	2 years
Expected dividends	0.00%
Range of risk-free interest rates	0.60%	0.40%	0.60%	0.40%
Performance Stock Unit
Share based Compensation Arrangement by Share based Payment Award, Fair Value Assumptions, Method Used [Line Items]
Range of expected volatilities			30.00%	34.00%
Expected dividends	0.00%		0.00%
Range of risk-free interest rates			0.10%	0.10%