Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2021

Summary of Stock-Based Compensation Expense Related to Equity Incentive Rewards

The Company recognized total stock-based compensation cost related to equity incentive awards as follows (in thousands):

	For the Year Ended December 31,
	2021		2020		2019
Stock-based compensation cost:
Stock options	$	11,966	$	15,402	$	16,489
Restricted stock units		67,501		35,318		16,322
Performance share units		16,011		—		—
Employee stock purchase plan		4,595		3,987		3,326
Total stock-based compensation cost	$	100,073	$	54,707	$	36,137

Summary of Stock Option Activity

The following table summarizes stock option activity for the Company’s stock-based compensation plans for 2021:

						Weighted
				Weighted		Average		Aggregate
				Average		Remaining		Intrinsic
				Exercise		Contractual		Value
	Shares			Price		Life (in Years)		(in thousands)
Options outstanding as of January 1, 2021		3,537,014		$	28.17		6.89	$	483,577
Options granted		—		$	—
Options exercised		(1,223,395	)	$	17.80
Options cancelled or expired		(34,830	)	$	42.24
Options outstanding as of December 31, 2021		2,278,789		$	33.52		6.30	$	217,824
Options exercisable as of December 31, 2021		1,753,067		$	27.80		5.97	$	177,609

Summary of Options Outstanding and Vested by Range of Exercise Prices

A summary of options outstanding and vested as of December 31, 2021, is as follows:

	Options Outstanding				Options Vested and Exercisable
Exercise	Number		Weighted Average		Number Vested		Weighted Average
Prices	Outstanding		Life (in Years)		and Exercisable		Life (in Years)
$1.90 to $6.40		18,612		1.1		18,612		1.1
$8.04 to $11.72		72,717		2.3		72,717		2.3
$12.20 to $15.06		380,304		4.7		380,304		4.7
$16.06 to $24.00		706,791		6.1		639,948		6.1
$31.99 to $42.21		655,237		7.0		441,953		7.0
$55.10 to $99.65		410,736		7.8		185,749		7.8
$124.35 to $151.76		34,392		7.8		13,784		6.5
		2,278,789				1,753,067

Summary of Fair Value Estimated Using Black-Scholes Option Pricing Model Assumptions

For the options granted during the periods presented, the fair value was estimated using the Black-Scholes option-pricing model with the following assumptions:

	For the Year Ended December 31,
	2021		2020	2019
Fair market value of common stock		—	$66.26 - $151.76	$39.76 - $79.25
Volatility		—	43% - 44%	40%
Expected term		—	5-6 years	5-6 years
Expected dividend yield		—	n/a	n/a
Risk-free interest rate		—	0.33% - 1.25%	1.68% - 2.65%

Summary of RSU Activity

The following table summarizes RSU activity for the Company’s stock-based compensation plans for 2021:

				Weighted
				Average
				Grant Date Fair
	Restricted Stock Units			Value Per Share
RSUs outstanding as of January 1, 2021		2,359,063		$	70.17
RSUs granted		1,282,177		$	138.79
RSUs vested		(524,246	)	$	68.36
RSUs cancelled		(255,031	)	$	90.66
RSUs outstanding as of December 31, 2021		2,861,963		$	99.41

Summary of PSU Activity

The following table summarizes PSU activity for the Company’s stock-based compensation plans for 2021:

				Weighted
				Average
	Performance Share			Grant Date Fair
	Units			Value Per Share
PSUs outstanding as of January 1, 2021		—		$	—
PSUs granted		120,632		$	147.39
PSUs vested		—		$	—
PSUs cancelled		(5,742	)	$	150.00
PSUs outstanding as of December 31, 2021		114,890		$	147.26

2018 Employee Stock Purchase Plan

Summary of Fair Value Estimated Using Black-Scholes Option Pricing Model Assumptions

For the years ended December 31, 2021, 2020, and 2019, the fair value of ESPP purchase rights was estimated using the Black-Scholes option-pricing model with the following assumptions:

		For the Year Ended December 31,
	2021		2020		2019
Fair market value of common stock	$152.35 to $166.84			$87.23 to $138.83		$40.60 to $82.12
Volatility	31% to 34%			32% to 49%		40%
Expected term	0.5 years			0.5 years		0.5 years
Expected dividend yield	n/a			n/a		n/a
Risk-free interest rate	0.06% to 0.08%			0.11% to 1.54%		2.04% to 2.59%