Stock-Based Compensation Expense and Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2021

Compensation Related Costs [Abstract]

Schedule of Weighted-Average Valuation Assumptions

We used the following weighted-average assumptions in applying the Black-Scholes valuation model for determination of option valuation:

	Years Ended December 31,
	2021	2020	2019
Risk-free interest rate	—	0.6%	1.7% - 2.6%
Expected term (years)	—	6.6	6.4 - 6.7
Expected dividend yield	—	—	—
Expected volatility	—	71.0%	45.7% - 50.2%

We used the following weighted-average assumptions in applying the Black-Scholes valuation model for determination of the 2018 ESPP share valuation:

	Years Ended December 31,
	2021	2020
Risk-free interest rate	0.1% - 2.8%	0.12%- 1.51%
Expected term (years)	0.5 - 2.0	0.5 - 2.0
Expected dividend yield	—	—
Expected volatility	95.0% - 114.5%	61.0% - 119.2%

Schedule of Employee and Non-Employee Stock-Based Compensation Expense

The following table summarizes the components of stock-based compensation expense in the consolidated statements of operations (in thousands):

	Years Ended December 31,
	2021		2020		2019
Cost of revenue	$	13,811	$	17,475	$	45,429
Research and development	20,274		19,037		40,949
Sales and marketing	17,085		10,997		32,478
General and administrative	24,962		26,384		77,435
	$	76,132	$	73,893	$	196,291

Schedule of Stock Option and RSU Activity

The following table summarizes the stock option activity under our stock plans during the reporting period:

	Outstanding Options
	Number of Shares	Weighted Average Exercise Price		Remaining Contractual Life (Years)	Aggregate Intrinsic Value
					(in thousands)
Balances at December 31, 2019	17,837,316	$	20.76	6.9	$	14,964
Granted	200,000	7.30
Exercised	(1,341,324)	11.18
Cancelled	(1,341,721)	22.49
Balances at December 31, 2020	15,354,271	21.27		6.0	129,855
Exercised	(3,460,364)	23.05
Cancelled	(1,156,612)	16.33
Balances at December 31, 2021	10,737,295	21.23		5.2	60,304
Vested and expected to vest at December 31, 2021	10,620,061	21.36		5.2	58,772
Exercisable at December 31, 2021	8,858,957	23.67		4.8	36,441

The following table presents the stock activity and the total number of shares available for grant under our stock plans as of December 31, 2021:

	Plan Shares Available for Grant
Balances at December 31, 2020	20,233,754
Added to plan	8,102,014
Granted	(6,475,536)
Cancelled	2,778,276
Expired	(491,724)
Balances at December 31, 2021	24,146,784

Schedule of RSU Activity and Related Information

A summary of our stock awards activity and related information is as follows:

	Number of Awards Outstanding	Weighted Average Grant Date Fair Value
Unvested Balance at December 31, 2019	10,112,266	$	17.29
Granted	4,744,467	12.43
Vested	(7,806,038)	17.48
Forfeited	(631,907)	14.93
Unvested Balance at December 31, 2020	6,418,788	$	13.71
Granted	6,475,536	25.82
Vested	(2,904,996)	17.04
Forfeited	(1,621,664)	20.97
Unvested Balance at December 31, 2021	8,367,664	20.52