Convertible Preferred Stock (Details) (Warrants to purchase convertible preferred stock, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Jan. 31, 2013	Jan. 31, 2012
Fair value of the preferred stock warrant liability
Expense arising from revaluation	$ 14,087	$ 2,034
Changes in the fair value of the preferred stock warrant liability
Balance at beginning of period	2,133	1,013
Change in fair value of preferred stock warrants	14,087	2,034
Exercises		(914)
Conversion of preferred stock warrants to common stock warrants	(16,220)
Balance at end of period		$ 2,133
Minimum
Assumptions used to estimate the value of the preferred stock warrants
Expected volatility (as a percent)	49.70%	49.40%
Risk-free rate (as a percent)	0.50%	0.39%
Expected term	3 years 4 months 17 days	2 years 7 months 24 days
Maximum
Assumptions used to estimate the value of the preferred stock warrants
Expected volatility (as a percent)	53.20%	57.10%
Risk-free rate (as a percent)	1.40%	1.09%
Expected term	6 years 3 months 18 days	7 years 2 months 19 days