Stockholders' Equity and Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of Stock Options Activity

The following is a summary of stock options activity for the year ended December 31, 2020:

	Stock Options
	Number of Shares			Weighted Average Exercise Price		Aggregate Intrinsic Value (in thousands)		Weighted Average Remaining Contractual Term (in years)
Outstanding at December 31, 2019		15,812,928		$	14.67	$	50,994		7.4
Granted		2,649,800		$	21.46
Exercised		(3,088,076	)	$	13.66
Forfeited		(244,623	)	$	14.42
Expired		(29,887	)	$	14.74
Outstanding, vested and expected to vest at December 31, 2020		15,100,142		$	16.07	$	143,156		6.9
Vested and exercisable at December 31, 2020		10,428,449		$	15.38	$	106,006		6.2

Summary of Estimated Fair Value of Stock Options Granted Using Weighted-average Assumptions

The Company used the Black-Scholes-Merton option pricing model to estimate the fair value of stock options granted using the following weighted-average assumptions:

	Year Ended December 31,
	2020	2019	2018
Expected life (in years)	5.8	5.9	5.8
Risk-free interest rate	1.2%	2.2%	2.8%
Volatility	49%	46%	48%
Dividend yield	—%	—%	—%
Fair value of common stock	$21.46	$14.17	$13.31

Summary of Estimated Fair Value of ESPP Purchase Rights Granted Using Weighted-average Assumptions

The Company used the Black-Scholes-Merton option pricing model to estimate the fair value of ESPP purchase rights granted using the following weighted-average assumptions:

	Year Ended December 31,
	2020	2019	2018
Expected life (in years)	1.3	1.2	1.3
Risk-free interest rate	0.1%	1.9%	2.7%
Volatility	56%	42%	39%
Dividend yield	—%	—%	—%
Fair value of common stock	$20.42	$17.00	$12.89

Summary of Stock-based Compensation Expense Recognized in Financial Statements

Stock-based compensation expense recognized in the consolidated financial statements is as follows:

	Year Ended December 31,
(in thousands)	2020		2019		2018
Cost of revenue	$	4,450	$	3,658	$	8,931
Research and development		30,693		21,159		48,739
Sales and marketing		19,707		11,950		19,046
General and administrative		24,317		23,478		55,054
Stock-based compensation expense, net of amounts capitalized		79,167		60,245		131,770
Capitalized stock-based compensation expense		2,243		3,503		2,609
Stock-based compensation expense	$	81,410	$	63,748	$	134,379

Summary of Unamortized Stock-based Compensation

As of December 31, 2020, unamortized stock-based compensation was as follows:

	Unrecognized stock-based compensation (in thousands)		Weighted average vesting period (in years)
Restricted stock units (service-based)	$	108,731	2.4
Restricted stock units (performance-based)		932	0.8
Stock options		34,736	2.1
Restricted stock awards		1,560	1.2
ESPP		6,100	1.7
Total unrecognized stock-based compensation	$	152,059

Restricted Stock Units

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of Restricted Stock Units Activity and Restricted Stock Awards Activity

The following is a summary of restricted stock units activity for the year ended December 31, 2020:

	Restricted Stock Units
	Number of Shares			Weighted Average Grant-Date Fair Value		Weighted Average Remaining Contractual Term (in years)
Unvested at December 31, 2019		6,975,994		$	14.72		2.2
Granted		5,091,244		$	19.43
Vested		(4,115,357	)	$	15.07
Forfeited/cancelled		(951,026	)	$	16.25
Unvested at December 31, 2020		7,000,855		$	17.72		1.1

Restricted Stock Awards

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Summary of Restricted Stock Units Activity and Restricted Stock Awards Activity

The following is a summary of restricted stock awards activity for the year ended December 31, 2020:

	Restricted Stock Awards
	Number of Shares			Weighted Average Grant-Date Fair Value		Weighted Average Remaining Contractual Term (in years)
Unvested at December 31, 2019		299,798		$	18.30		2.3
Vested		(197,338	)	$	18.30
Unvested at December 31, 2020		102,460		$	18.30		1.2