Employee Benefits and Stock-based Compensation (Tables)

12 Months Ended

Jan. 31, 2021

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,
	2021		2020		2019
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,328	$	1,184	$	1,261
Research and development		42,903		41,842		37,432
Selling, general and administrative		25,903		23,845		22,119
Total stock-based compensation	$	70,134	$	66,871	$	60,812

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,
	2021			2020			2019
Stock Options:
Volatility		52	%		52	%		54	%
Risk-free interest rate		0.52	%		1.82	%		2.77	%
Expected term (years)		5.78			6.01			5.41
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		59	%		47	%		45	%
Risk-free interest rate		0.21	%		2.23	%		2.15	%
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, 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
Granted		51,200			59.54	$	28.37
Exercised		(421,736	)		24.52			$	19,401
Forfeited		(11,618	)		46.69
Expired		(23,349	)		70.11
Outstanding at January 31, 2021		719,143		$	38.33					4.42		$	40,358
Exercisable at January 31, 2021		592,729		$	35.27						3.56	$	35,092

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, 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
Granted		1,499,203			53.45
Vested		(1,162,883	)		50.53
Forfeited		(81,785	)		54.48
Unvested at January 31, 2021		2,871,801		$	51.73