Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Schedule of Valuation Assumptions for Stock Options

The Company records compensation expense for stock options based on the estimated fair value of the options on the date of grant using the Black-Scholes option-pricing model with the assumptions set forth in the table below.

	Year Ended December 31,				Nine Months Ended September 30,
	2019		2020		2020		2021
					(unaudited)
Expected term (years)	6.3		4.0 - 6.3		5.6		6.3
Expected stock price volatility	40.0% - 45.0%		45.0% - 50.0%		48.0	%	45.0	%
Risk-free interest rate	1.4% - 2.5%		0.2% - 1.7%		0.8	%	0.8	%
Dividend yield	—	%	—	%	—	%	—	%
Fair value of common stock	$1.07 - $4.07		$4.14 - $5.84		$4.14 - $5.71		$19.82

Summary of Common Stock Option Activity

The following table summarizes the common stock option activity for the years ended December 31, 2019 and 2020 and for the nine months ended September 30, 2021 (unaudited):

	Number of Shares	Weighted-Average Exercise Price		Weighted-Average Grant Date Fair Value		Weighted-Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (in thousands)
Options outstanding at December 31, 2018	17,101,000	$	0.52	$	0.20	7.5	$	10,328
Granted	3,114,240	2.90		1.60
Exercised	(1,947,760)	0.19					6,046
Repurchased	(7,136,480)	0.24
Canceled, forfeited or expired	(766,480)	0.98
Options outstanding at December 31, 2019	10,364,520	$	1.47	$	0.71	8.1	$	18,952
Granted	5,060,720	4.93		2.22
Exercised	(328,600)	0.68					3,724
Canceled, forfeited or expired	(876,840)	1.92
Options outstanding at December 31, 2020	14,219,800	$	2.73	$	1.25	7.9	$	131,893
Granted	40,000	12.01		11.52			312
Exercised	(3,173,728)	1.84		0.71			58,274
Canceled, forfeited or expired	(502,995)	4.07		1.70			8,216
Options outstanding at September 30, 2021	10,583,077	$	2.97	$	1.43	7.3	$	200,938
Options vested and exercisable at September 30, 2021	7,002,237	$	2.24	$	1.08	6.8	$	138,061

Schedule of Restricted Stock Unit Activity

The following table summarizes the RSUs activity for the for the nine months ended September 30, 2021 (unaudited):

	Shares	Weighted-Average Grant-Date Fair Value per share
Outstanding as of December 31, 2020	—	$	—
Granted	1,775,992	$	16.42
Vested	(954,297)	$	16.23
Forfeited or expired	(5,500)	$	28.94
Outstanding as of September 30, 2021	816,195	$	16.56

Schedule of Valuation Assumptions for Employee Stock Purchase Plan

The fair value of the ESPP purchase right is estimated on the grant date using the Black-Scholes option-pricing model with the following assumptions:

	Nine Months Ended September 30, 2021
	(unaudited)
Expected term (years)	0.5
Expected stock price volatility	60.9	%
Risk-free interest rate	0.4	%
Dividend yield	—	%

Schedule of Stock-based Compensation Expense

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

	Year Ended December 31,				Nine Months Ended September 30,
	2019		2020		2020		2021
					(unaudited)
Cost of revenues	$	83	$	188	$	122	$	253
Sales and marketing	5,750		1,579		825		7,277
Technology and development	162		896		323		530
General and administrative	112,110		2,571		1,983		15,212
Total stock-based compensation expense	$	118,105	$	5,234	$	3,253	$	23,272