Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

A summary of stock option activity is set forth below (in thousands, except share and per share data):

				Outstanding Awards
	Number of Shares Available for Grant			Number of Shares Underlying Outstanding Options			Weighted Average Exercise Price			Weighted Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value
Outstanding, January 1, 2018		38,055			963,435		$	2.02			9.27	$	4,977
Options authorized		837,000
Options granted		(210,452	)		210,452		$	2.26
Options exercised		—			(123,949	)	$	1.92
Options forfeited or cancelled		153,399			(153,399	)	$	2.25
Outstanding, December 31, 2018		818,002			896,539		$	2.04			8.57	$	2,436
Options authorized		814,184
Options granted		(1,124,430	)		1,124,430		$	5.39
Options exercised		—			(14,791	)	$	(2.12	)
Options forfeited or cancelled		145,380			(145,532	)	$	2.17
Outstanding, December 31, 2019		653,136			1,860,646		$	4.05			8.53	$	5,812
Assumed as part of the Merger		2,707,144			81,370		$	8.39
Options granted		(1,914,142	)		2,276,645		$	15.14
Options exercised					(210,752	)	$	2.18
Options forfeited or cancelled		293,483			(300,964	)	$	6.04
Outstanding, December 31, 2020		1,739,621			3,706,945		$	10.90			7.98	$	15,126
Shares exercisable December 31, 2020					1,219,904		$	4.64			5.11	$	11,563
Vested and expected to vest, December 31, 2020					3,706,945		$	10.90			7.98	$	15,126

Summary of Restricted Stock Activity

Activity with respect to restricted stock was as follows:

	Number of Shares Underlying Outstanding Restricted Stock			Weighted Average Grant Date Fair Value
Unvested, January 1, 2018		165,699		$	4.19
Vested		(134,516	)	$	4.19
Unvested, December 31, 2018		31,183		$	4.19
Vested		(31,183	)	$	4.19
Unvested, December 31, 2019		—		$	—

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	1,674	$	274	$	285
General and administrative		3,589		901		2,194
Total stock-based compensation	$	5,263	$	1,175	$	2,479

Schedule of Assumptions to Estimate Fair Value of Stock Options Using Black-Scholes Option Pricing Model

The Company estimated the fair value of stock options using the Black Scholes option-pricing model. The fair value of stock options is being amortized on a straight-line basis over the requisite service period of the awards. The fair value of stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2020	2019	2018
Expected volatility	72.6%-96.3%	71.5%-86.5%	73.3%-74%
Risk-free interest rate	0.1%-1.7%	1.6%-2.5%	2.7%-2.8%
Dividend yield	0%	0%	0%
Expected term	1.00-6.08 years	5.15-6.08 years	6.02-6.08 years