Employee Benefits and Stock-based Compensation (Tables)

12 Months Ended

Jan. 31, 2020

Postemployment Benefits [Abstract]

Classification of Stock-based Compensation

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

	Year Ended January 31,
	2020		2019		2018
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,184	$	1,261	$	1,306
Research and development		41,842		37,432		34,575
Selling, general and administrative		23,845		22,119		20,980
Total stock-based compensation	$	66,871	$	60,812	$	56,861

Weighted-Average Assumptions Used to Estimate Fair Value

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

	Year Ended January 31,
	2020			2019			2018
Stock Options:
Volatility		52	%		54	%		53	%
Risk-free interest rate		1.82	%		2.77	%		2.08	%
Expected term (years)		6.01			5.41			6.08
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		47	%		45	%		44	%
Risk-free interest rate		2.23	%		2.15	%		1.03	%
Expected term (years)		0.5			0.5			0.5
Dividend yield		0	%		0	%		0	%

Stock Option Activities

The following table summarizes stock option activities for the periods 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, 2017		1,703,524		$	21.66
Granted		132,250			54.66	$	28.28
Exercised		(175,187	)		12.50			$	7,446
Forfeited		(27,721	)		56.97
Expired		(21,522	)		36.31
Outstanding at January 31, 2018		1,611,344			24.56
Granted		116,600			42.73	$	21.75
Exercised		(232,205	)		5.54			$	8,867
Forfeited		(20,974	)		53.50
Expired		(15,701	)		54.35
Outstanding at January 31, 2019		1,459,064			28.31
Granted		66,850			50.56	$	25.35
Exercised		(366,886	)		15.52			$	13,263
Forfeited		(14,931	)		46.29
Expired		(19,451	)		64.53
Outstanding at January 31, 2020		1,124,646		$	32.93					4.35		$	31,295
Exercisable at January 31, 2020		960,567		$	30.24						3.65	$	29,573

Restricted Stock and Restricted Stock Units Activities

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

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2017		2,175,673		$	56.76
Granted		1,052,235			47.11
Vested		(1,006,130	)		47.55
Forfeited		(118,497	)		54.72
Unvested at January 31, 2018		2,103,281			56.45
Granted		1,367,751			40.03
Vested		(994,500	)		53.27
Forfeited		(81,016	)		53.57
Unvested at January 31, 2019		2,395,516			48.49
Granted		1,329,288			54.54
Vested		(1,012,581	)		51.24
Forfeited		(94,957	)		54.26
Unvested at January 31, 2020		2,617,266		$	50.30