Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 six months ended June 30, 2021:

	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2021		3,410,979		$	3.55
Granted		989,488			35.62
Forfeited		(37,677	)		22.46
Vested		(860,788	)		1.83
Unvested at June 30, 2021		3,502,002		$	12.83

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		9.6	$	81,822
Granted		2,158,388			33.73		—		—
Exercised		—			—		—		—
Forfeited		(34,225	)		29.43		—		53
Options outstanding at June 30, 2021		6,097,072		$	23.40		9.3	$	11,256
Options vested and exercisable at June 30, 2021		184,361		$	14.37		9.0	$	990

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 June 30, 2021			Six Months Ended June 30, 2021
Expected term (in years)		6.00			6.05
Expected volatility		94.73	%		95.06	%
Risk-free interest rate		1.07	%		0.83	%
Expected dividend yield		—			—
Fair value of common stock	$	23.28		$	33.73

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was as follows:

	Three Months Ended June 30,				Six Months Ended June 30,
(in thousands)	2021		2020		2021		2020
Research and development	$	3,953	$	94	$	7,264	$	308
General and administrative		5,773		398		10,565		830
Total stock-based compensation expense	$	9,726	$	492	$	17,829	$	1,138