Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 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 three months ended March 31, 2021:

	Shares			Weighted Average Grant Date Fair Value
Unvested at January 1, 2021		3,410,979		$	3.55
Granted		635,613			42.32
Forfeited		(7,000	)		36.80
Vested		(519,839	)		1.86
Unvested at March 31, 2021		3,519,753		$	10.74

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		1,186,138			42.30		—		—
Exercised		—			—		—		—
Forfeited		(14,000	)		36.80		—		—
Options outstanding at March 31, 2021		5,145,047		$	23.43		9.4	$	24,616
Options vested and exercisable at March 31, 2021		28,009		$	6.76		8.8	$	466

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 March 31, 2021
Expected term (in years)		6.10
Expected volatility		95	%
Risk-free interest rate		0.64	%
Expected dividend yield		—
Fair value of common stock	$	42.30

Schedule of Stock-based Compensation Expense

Stock-based compensation expense was as follows:

	Three Months Ended March 31,
(in thousands)	2021		2020
Research and development	$	3,311	$	214
General and administrative		4,792		432
Total stock-based compensation expense	$	8,103	$	646