Stock Compensation Plans (Details 4)	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012	Jan. 31, 2011
ESPP
Assumptions used to determine the fair value of options
Expected volatility, minimum (as a percent)	42.00%
Expected volatility, maximum (as a percent)	49.10%
Risk-free rate, minimum (as a percent)	0.10%
Risk-free rate, maximum (as a percent)	0.19%
ESPP | Minimum
Assumptions used to determine the fair value of options
Expected term	6 months
ESPP | Maximum
Assumptions used to determine the fair value of options
Expected term	1 year 1 month 28 days
Options | Employees
Assumptions used to determine the fair value of options
Expected volatility, minimum (as a percent)	50.00%	48.40%	51.80%
Expected volatility, maximum (as a percent)	53.20%	56.50%	54.10%
Risk-free rate, minimum (as a percent)	0.82%	0.92%	1.48%
Risk-free rate, maximum (as a percent)	1.41%	2.47%	2.92%
Options | Employees | Minimum
Assumptions used to determine the fair value of options
Expected term	5 years 10 months 24 days	5 years 3 months	5 years 5 months 12 days
Options | Employees | Maximum
Assumptions used to determine the fair value of options
Expected term	6 years 1 month 17 days	6 years 29 days	6 years 29 days
Options | Nonemployees
Assumptions used to determine the fair value of options
Expected volatility, minimum (as a percent)	49.70%	52.60%	66.10%
Expected volatility, maximum (as a percent)	51.70%	58.00%	66.10%
Risk-free rate, minimum (as a percent)	1.38%	1.70%	3.39%
Risk-free rate, maximum (as a percent)	1.87%	1.80%	3.39%
Options | Nonemployees | Minimum
Assumptions used to determine the fair value of options
Expected term	8 years 18 days	9 years 22 days	9 years 11 months 23 days
Options | Nonemployees | Maximum
Assumptions used to determine the fair value of options
Expected term	9 years 4 months 6 days	9 years 10 months 17 days	9 years 11 months 23 days