Stock-based Compensation (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2021

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Summary of Stock-based Payment Arrangement Expenses

The Company recognized stock-based compensation expense for the periods indicated as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2020		2021		2020		2021
Cost of revenue	$	126	$	922	$	204	$	1,504
Sales and marketing		1,571		4,774		2,812		8,814
Research and development		6,823		20,110		10,692		40,148
General and administrative		2,348		8,919		5,654		41,362
Total	$	10,868	$	34,725	$	19,362	$	91,828

The Company recognized stock-based compensation expense for the periods indicated as follows (in thousands):

	2018		2019		2020
Cost of revenue	$	517	$	124	$	982
Sales and marketing		2,582		1,922		10,668
Research and development		1,009		5,009		36,852
General and administrative		1,357		3,167		13,885
Total stock-based compensation expense	$	5,465	$	10,222	$	62,387

Summary Of Weighted Average Assumptions Used To Estimate The Fair Value Of Options Granted

The weighted-average assumptions used to estimate the fair value of stock options granted are as follows:

	Year Ended December 31,
	2018			2019			2020
Weighted-average expected term		6.00			6.05			5.94
Expected volatility		62	%		43	%		39	%
Risk-free interest rate		2.58	%		1.91	%		0.56	%
Dividend yield		0	%		0	%		0	%

Summary Of Stock Options Activity Under The Plan

The Company’s activity of the stock options under the Plan for the years ended December 31, 2019 and 2020 was as follows:

	Number of Options			Weighted Average Exercise Price Per Share		Weighted Average Remaining Contractual Term (Years)
Balances at December 31, 2018		8,370,552		$	2.66		9.2
Granted		12,199,200			4.36
Exercised		(1,011,873	)		2.61
Forfeited		(1,158,528	)		2.82
Expired		(4,221	)		2.81
Balances at December 31, 2019		18,395,130		$	3.78		9.2
Granted		13,158,430			8.41
Exercised		(871,668	)		2.65
Forfeited		(425,001	)		1.68
Expired		(1,367,367	)		4.64
Balances at December 31, 2020		28,889,524		$	5.92		8.8
Vested and exercisable at December 31, 2020		17,099,956		$	5.26		8.6
Vested and expected to vest at December 31, 2020		25,023,502		$	6.22		8.9

Summary Of Oustanding Restricted Stock Awards Activity

The Company’s activity of the outstanding restricted stock awards for Class A common stock for the years ended December 31, 2019 and 2020, was as follows:

	Number of Restricted Stock Awards			Weighted Average Grant Date Fair Value per Share
Balances at December 31, 2018		3,664,653		$	1.68
Granted		3,267,792			1.97
Repurchased		(59,637	)		1.68
Vested		(2,948,394	)		1.83
Balances at December 31, 2019		3,924,414		$	1.81
Granted		—			—
Repurchased		—			—
Vested		(2,687,643	)		1.85
Balances at December 31, 2020		1,236,771		$	1.71