Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Summary of Stock Option Activity

A summary of the stock option activity is as follows, in thousands, except per share amounts and term information:

						Weighted
				Weighted		Average
				Average		Remaining	Aggregate
				Exercise		Contractual	Intrinsic
	Shares			Price		Term	Value
Outstanding at December 31, 2019		16,850		$	3.82
Granted		10,019			8.78
Exercised		(3,769	)		2.87
Expired / Cancelled / Forfeited		(1,572	)		4.93
Outstanding at December 31, 2020		21,528		$	6.22	8.1 years	$	734,604
Exercisable at December 31, 2020		9,012		$	3.73	7.1 years	$	329,945

Assumptions Used in Black-Scholes Model to Determine Fair Value for Stock Option Awards Granted

All stock options outstanding at December 31, 2020 are options to purchase shares of Class A Common Stock. The fair value of option awards issued with service and performance vesting conditions are estimated on the grant date using the Black-Scholes option pricing model. The following table summarizes the assumptions used:

	Year Ended December 31,
	2020		2019		2018
Risk-free interest rate	0.4% - 1.4%		1.4% - 2.4%		2.7% - 2.9%
Expected term	5.3 - 6.3 years		5.6 - 6.3 years		5.7 - 6.1 years
Expected stock price volatility	50% - 62%		50%		60%
Dividend yield		—		—		—
Fair value of common stock per share	$5.94 - $33.00		$2.75 - $5.88		$1.05 - $2.75

Summary of Cash Bonuses Paid to Vested Option Holders Included in Components of Expenses on Accompanying Consolidated Statement of Operations

In connection with the dividend payments made to stockholders in May 2018 and October 2018, as further described in “Note 14. Redeemable Convertible Preferred Stock and Stockholders’ Equity (Deficit),” the Company paid vested option holders cash bonuses totaling $38.8 million which are included in the following components of expenses on the accompanying consolidated statement of operations for the year ended December 31, 2018 as follows:

Cost of revenue	$	—
Product development and technology		29,189
Sales and marketing		6,878
General and administrative		2,733
	$	38,800

Restricted Stock

Summary of Restricted Stock Activity

A summary of the Restricted Stock Awards and Restricted Stock Unit activity is as follows:

	Restricted			Restricted Stock Units for Class A			Restricted Stock Units for Class B				Weighted Average
	Stock			Common			Common				Grant Date
(in thousands, except per share amounts)	Awards			Stock			Stock				Fair Value
Nonvested restricted stock awards or restricted    stock units at December 31, 2019		1,879			—			—			$	3.88
Granted		—			2,800			24,633				23.56
Vested		(470	)		(8	)		(16,935	)	(1)		19.26
Forfeited		—			(2	)		—				49.05
Nonvested restricted stock awards or restricted    stock units at December 31, 2020		1,409			2,790			7,698			$	26.74
(1)Includes 15,691 of restricted stock units vested but not yet settled related to the Performance-Vesting Founders Awards.