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Stock-based Compensation (Tables)
3 Months Ended
Mar. 31, 2021
Share-based Payment Arrangement [Abstract]  
Schedule of Stock-based Awards The following table summarizes the stock options activity under the 2010 Plan and 2019 Plan for the three months ended March 31, 2021:
Stock Options Outstanding
(in thousands, except year and per share data)
Shares Subject to Options OutstandingWeighted- Average Exercise Price per OptionWeighted- Average Remaining Contractual Terms (in years)Aggregate Intrinsic Value
Balances as of December 31, 202018,186 $3.92 7.0$1,310,650 
Options granted — $— 
Options exercised (1,282)$6.25 $93,204 
Options canceled/forfeited/expired (71)$2.73 
Balances as of March 31, 202116,833 $3.75 6.7$1,119,535 
Vested and expected to vest as of March 31, 202116,813 $3.75 6.7$1,118,271 
Exercisable as of March 31, 202115,555 $2.58 6.5$1,052,717 
Schedule of Assumptions Used to Determine the Fair Value of Stock Options Granted The weighted-average assumptions used to determine the fair value of stock options granted during the three months ended March 31, 2020 were as follows:
Three Months ended March 31,
2020
Expected term (in years)6.1
Expected volatility40.0 %
Risk-free interest rate1.5 %
Dividend yield— 
Schedule of Restricted Stock Units Activity
RSU and restricted stock activity for the three months ended March 31, 2021 was as follows:

Restricted Stock and RSUsWeighted-Average
Grant
Date Fair Value
(in thousands, except per share data)
Unvested and outstanding as of December 31, 20208,629 $21.38 
Granted - RSUs637 $82.58 
Granted - Restricted stock— $— 
Vested - RSUs(649)$15.32 
Vested - Restricted stock— $— 
Forfeited (170)$25.78 
Unvested as of March 31, 20218,447 $26.52 
Vested and not yet released
Outstanding as of March 31, 20218,447 
Schedule of Fair Value Assumptions for Employee Stock Purchase Plan
The weighted-average assumptions used to determine the fair value of the ESPP during the periods presented were as follows:
Three Months ended March 31,
20212020
Expected term (in years)0.50.6
Risk-free interest rate0.1 %1.8 %
Expected volatility59.7 %35.5 %
Dividend yield— — %
Schedule of Stock-based Compensation Expense
The following table sets forth the total stock-based compensation expense included in the Company’s condensed consolidated statements of operations:

Three Months Ended March 31,
20212020
(in thousands)
Cost of revenue$414 $267 
Sales and marketing5,645 3,163 
Research and development8,364 6,090 
General and administrative3,615 3,377 
Total stock-based compensation expense
$18,038 $12,897