Equity-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Schedule of Equity-Based Compensation Expense

Equity-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
	(In thousands)
Research and development	$	9,017	$	2,775	$	18,643	$	7,325
General and administrative		6,393		2,625		13,805		6,996
Total	$	15,410	$	5,400	$	32,448	$	14,321

Summary of Restricted Stock Activity

The following table summarizes the Company’s restricted stock activity for the nine months ended September 30, 2021:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock units as of December 31, 2020		193,936		$	23.98
Granted		354,072			63.13
Vested		(50,946	)		17.80
Cancelled		(53,777	)		38.02
Unvested restricted stock units as of September 30, 2021		443,285		$	54.26

Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted

Weighted average assumptions used to apply this pricing model were as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2021	2020	2021	2020
Risk-free interest rate	1.0%	0.4%	0.9%	0.9%
Expected life of options	6.0 years	6.0 years	6.0 years	5.5-6.0 years
Expected volatility of underlying stock	75.2%	70.8%	72.7%	67.6%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%

Summary of Stock Option Activity

The following is a summary of stock option activity for the nine months ended September 30, 2021:

	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding at December 31, 2020		6,977,440		$	15.43
Granted		2,435,102			79.17
Exercised		(2,636,437	)		15.12
Forfeited		(559,241	)		29.80
Outstanding at September 30, 2021		6,216,864		$	39.23		8.01	$	601,927
Exercisable at September 30, 2021		1,977,984