Stock-based Compensation (Tables)

9 Months Ended

Oct. 31, 2013

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Classification of Stock-based Compensation

The following table presents the classification of stock-based compensation for the periods indicated:

	Three Months Ended October 31,				Nine Months Ended October 31,
	2013		2012		2013		2012
	(in thousands)
Stock-based compensation:
Cost of revenue	$	47	$	30	$	115	$	59
Research and development		1,385		905		3,259		1,979
Selling, general and administrative		1,029		550		2,286		1,403
Total stock-based compensation	$	2,461	$	1,485	$	5,660	$	3,441

Weighted-Average Assumptions Used to Estimate Fair Value

The following table sets forth the weighted-average assumptions used to estimate the fair value of stock options and employee stock purchase plan awards for the periods indicated:

	Three Months Ended October 31,						Nine Months Ended October 31,
	2013			2012			2013			2012
Stock Options:
Volatility		65	%		66	%		65	%		66	%
Risk-free interest rate		2.03	%		0.89	%		1.44	%		0.93	%
Expected term (years)		6.05			6.05			6.05			6.05
Dividend yield		0	%		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		52	%		51	%		52	%		51	%
Risk-free interest rate		0.04	%		0.18	%		0.04	%		0.18	%
Expected term (years)		0.5			0.94			0.5			0.94
Dividend yield		0	%		0	%		0	%		0	%

Stock Option Activities

The following table summarizes stock option activities for the nine months ended October 31, 2013:

	Option Outstanding
	Shares			Weighted- Average Exercise Price		Weighted- Average Grant-date Fair Value		Total Intrinsic Value of options Exercised (in thousands)		Weighted- Average Remaining Contactual Term (in years)		Aggregate Intrinsic Value (in thousands)
Outstanding at January 31, 2013		4,344,535			6.07
Granted		192,220			15.90	$	9.50
Exercised		(713,498	)		5.33			$	8,239
Forfeited		(59,901	)		9.88
Outstanding at October 31, 2013		3,763,356			6.65						6.44	$	52,314
Exercisable at October 31, 2013		2,839,311			5.62						5.88	$	42,405
Vested and expected to vest at October 31, 2013		3,715,813			6.60						6.41	$	51,819

Restricted Stock Unit Activities

The following table summarizes restricted stock unit activities for the nine months ended October 31, 2013:

	Shares			Weighted- Average Grant-Date Fair Value
Unvested at January 31, 2013		339,217		$	9.99
Granted		1,240,472			14.58
Released		(85,806	)		10.19
Forfeited		(10,052	)		10.63
Unvested at October 31, 2013		1,483,831		$	13.81