Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense recorded in the consolidated statements of operations was as follows (in thousands):

	Year Ended December 31,
	2021		2020		2019
Platform operations	$	15,913	$	8,794	$	5,350
Sales and marketing		50,671		29,726		20,769
Technology and development		57,791		36,672		26,553
General and administrative		213,038		36,583		28,086
Total	$	337,413	$	111,775	$	80,758

Summary of Stock Option Activity

The following summarizes stock option activity:

	Shares Under Option (in thousands)			Weighted- Average Exercise Price		Weighted- Average Contractual Life (years)		Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2020		26,481		$	10.73
Granted		1,212			74.85
Exercised		(7,361	)		8.36
Expired/forfeited		(1,348	)		19.18
Outstanding as of December 31, 2021		18,984		$	15.14		6.4	$	1,452,528
Exercisable as of December 31, 2021		13,008		$	8.69		5.7	$	1,079,090

Schedule of Weighted-Average Assumptions Used to Value Options Granted to Employees

The fair value of options on the date of grant was estimated based on the Black-Scholes option pricing model. The weighted- average assumptions used to value options granted to employees for the periods presented were as follows:

	Year Ended December 31,
	2021			2020			2019
Expected term (years)		6.0			6.0			6.0
Expected volatility		64.3	%		60.5	%		53.2	%
Risk-free interest rate		1.04	%		0.57	%		2.26	%
Estimated dividend yield		—	%		—	%		—	%

Summary of Restricted Stock Activity

The following summarizes restricted stock activity:

	Shares (in thousands)			Weighted- Average Grant Date Fair Value Per Share
Unvested as of December 31, 2020		5,698		$	26.10
Granted		2,818			77.41
Vested		(2,225	)		24.80
Forfeited		(694	)		33.48
Unvested as of December 31, 2021		5,597		$	51.54

Schedule of Weighted-Average Assumptions Used to Estimate the Fair Value of ESPP Shares

The fair value of ESPP shares was estimated using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Year ended December 31,
	2021			2020			2019
Expected term (years)		0.6			0.6			0.7
Expected volatility		62.3	%		61.9	%		53.2	%
Risk-free interest rate		0.09	%		0.40	%		2.08	%
Estimated dividend yield		—	%		—	%		—	%

Performance Option

Schedule of Weighted-Average Assumptions Used to Value Options Granted to Employees

The CEO Performance Option has an exercise price of $68.29 per share and a grant-date fair value of approximately $819.0 million, which was estimated based on a Monte Carlo valuation model using the following assumptions:

Expected volatility	63.4	%
Risk-free interest rate	1.55	%
Estimated dividend yield	—	%