Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2020

Employee Benefit Plans

Assumptions made for the purpose of estimating fair value

	2020	2019	2018
Expected term of options (years)	6	6	6
Risk free interest rate	0.37% - 1.37%	1.52% - 2.53%	2.81% - 2.88%
Volatility	64.19% - 68.18%	69.32% - 87.94%	98.31% - 98.89%

Schedule of Share-based Compensation, Stock Options, Activity

A summary of stock option activity for the year December 31, 2020 is as follows (in thousands except share amounts):

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
		Exercise		Contractual	Intrinsic
	Shares	Price		Terms	Value
Options outstanding at December 31, 2019	23,013,590	$	2.48	6.6	$	22,277
Granted	3,509,549		12.79	—		—
Exercised	(16,159,742)		2.55	—		—
Forfeited	(73,249)		6.32	—		—
Expired	(5,650)		4.78	—		—
Options outstanding at December 31, 2020	10,284,498	$	5.78	7.8	$	289,316
Options exercisable at December 31, 2020	4,084,124		2.31	5.8		129,068
Options unvested at December 31, 2020	6,200,374	$	8.07	9.1	$	160,248

Nonvested Restricted Stock Shares Activity

A summary of restricted stock activity for the year ended December 31, 2020 is as follows (in thousands except share amounts):

		Aggregate
		Intrinsic
	Shares	Value
Unvested restricted stock at December 31, 2019	4,608,560	$	—
Granted	3,227,149		—
Vested	(1,896,901)		—
Forfeited	(64,166)
Unvested restricted stock at December 31, 2020	5,874,642	$	199,209