Stock-Based Compensation and Employee Benefit Plan (Tables)

12 Months Ended

Dec. 31, 2020

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,
	2020	2019	2018
Risk-free interest rate	0.6%	1.7% - 2.6%	2.5% - 3.1%
Expected term (years)	6.6	6.4 - 6.7	6.2 - 6.7
Expected dividend yield	—	—	—
Expected volatility	71.0%	45.7% - 50.2%	52.4% - 56.1%

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,
	2020	2019
Risk-free interest rate	0.12% - 1.51%	1.5% - 2.6%
Expected term (years)	0.5 - 2.0	0.5 - 2.0
Expected dividend yield	—	—
Expected volatility	61.0% - 119.2%	45.9% - 54.0%

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,
	2020		2019		2018
Cost of revenue	$	17,475	$	45,429	$	29,680
Research and development	19,037		40,949		39,029
Sales and marketing	10,997		32,478		32,284
General and administrative	26,384		77,435		67,489
	$	73,893	$	196,291	$	168,482

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, 2018	14,558,420	$	25.93	6.8	$	3,084
Granted	4,956,064	5.60
Exercised	(358,564)	4.26
Cancelled	(1,318,604)	25.33
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
Vested and expected to vest at December 31, 2020	14,976,706	21.55		5.9	122,813
Exercisable at December 31, 2020	10,311,316	26.37		4.9	39,569

The following table presents the stock activity and the total number of shares available for grant under our stock plans as of December 31, 2020:

	Plan Shares Available for Grant
Balances at December 31, 2018	17,457,847
Added to plan	7,585,422
Granted	(8,176,023)
Cancelled	2,289,290
Expired	(1,923,392)
Balances at December 31, 2019	17,233,144
Added to plan	7,179,751
Granted	(4,944,467)
Cancelled	1,965,801
Expired	(1,200,475)
Balances at December 31, 2020	20,233,754

Schedule of RSU Activity and Related Information

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

	Number of Awards Outstanding	Weighted Average Grant Date Fair Value
Unvested Balance at December 31, 2018	16,784,800	$	18.74
Granted	3,219,959	11.81
Vested	(8,921,807)	18.03
Forfeited	(970,686)	17.34
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