Stock-based Compensation (Tables)

6 Months Ended

Jul. 31, 2018

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 July 31,				Six Months Ended July 31,
	2018		2017		2018		2017
	(in thousands)
Stock-based compensation:
Cost of revenue	$	317	$	332	$	632	$	635
Research and development		9,367		8,649		18,127		16,626
Selling, general and administrative		5,446		5,454		10,566		10,146
Total stock-based compensation	$	15,130	$	14,435	$	29,325	$	27,407

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 July 31,						Six Months Ended July 31,
	2018			2017			2018			2017
Stock Options:
Volatility		55	%		53	%		55	%		53	%
Risk-free interest rate		2.77	%		1.88	%		2.73	%		2.08	%
Expected term (years)	5.38			6.08			5.36			6.07
Dividend yield		0	%		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		—			—			46	%		39	%
Risk-free interest rate		—			—			1.95	%		0.89	%
Expected term (years)		—			—			0.5			0.5
Dividend yield		—			—			0	%		0	%

Stock Option Activities

The following table summarizes stock option activities for the period indicated:

	Option Outstanding
										Weighted-
								Total Intrinsic		Average
						Weighted-		Value Of		Remaining		Aggregate
				Weighted-		Average		Options		Contractual		Intrinsic
				Average		Grant-date		Exercised		Term		Value
	Shares			Exercise Price		Fair Value		(in thousands)		(in years)		(in thousands)
Outstanding at January 31, 2018		1,611,344		$	24.56
Granted		60,050			45.74	$	23.43
Exercised		(195,179	)		4.85			$	7,838
Forfeited		(12,026	)		53.92
Expired		(6,637	)		44.39
Outstanding at July 31, 2018		1,457,552			27.74					4.81		$	24,385
Exercisable at July 31, 2018		1,234,750		$	23.17						4.13	$	24,377

Restricted Stock and Restricted Stock Units Activities

The following table summarizes restricted stock and restricted stock units activities for the period indicated:

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2018		2,103,281		$	56.45
Granted		368,369			44.72
Vested		(487,507	)		53.48
Forfeited		(23,926	)		53.12
Unvested at July 31, 2018		1,960,217		$	55.03