Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Restricted Common Stock Activity

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

	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2021		3,410,979		$	3.55
Granted		1,047,613			34.76
Forfeited		(94,709	)		25.44
Vested		(1,237,248	)		2.44
Unvested at September 30, 2021		3,126,635		$	13.79

Summary of Stock Option Activity

The following table summarizes stock option activity (in thousands, except share and per share data):

	Shares			Weighted Average Exercise Price		Weighted Average Contractual Life (in years)		Aggregate Intrinsic Value
Options outstanding at January 1, 2021		3,972,909		$	17.84		9.58	$	81,822
Granted		2,264,138			33.09		—		—
Exercised		(9,425	)		17.00		—		71
Forfeited		(199,146	)		25.29		—		948
Options outstanding at September 30, 2021		6,028,476		$	23.33		9.07	$	31,564
Options vested and exercisable at September 30, 2021		1,063,653		$	17.09		8.81	$	8,800

Schedule of Estimated Fair Value Assumptions Using Black Scholes Option-Pricing Model

The fair value was estimated on the date of grant using the Black Scholes option-pricing model, with the following weighted-average assumptions:

	Three Months Ended September 30, 2021			Nine Months Ended September 30, 2021
Expected term (in years)		6.09			6.06
Expected volatility		93.76	%		95.00	%
Risk-free interest rate		0.97	%		0.84	%
Expected dividend yield		—			—
Fair value of common stock	$	20.05		$	33.09

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
(in thousands)	2021		2020		2021		2020
Research and development	$	4,010	$	3,092	$	11,274	$	3,400
General and administrative		6,276		768		16,841		1,598
Total stock-based compensation expense	$	10,286	$	3,860	$	28,115	$	4,998