Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense recorded related to awards granted to employees and non-employees was as follows (in thousands):

	Year Ended December 31,
	2020		2019		2018
Research and development	$	1,234	$	956	$	410
General and administrative		2,375		1,212		540
Total stock-based compensation expense	$	3,609	$	2,168	$	950

Summary of Activity under Plans

Activity under the Company’s 2015 and 2019 Plans is set forth below:

				Outstanding Options
	Shares available for Grant			Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)
Balance, January 1, 2020		1,036,746			1,962,332		$	6.03		8.63
Additional shares authorized		813,578			—
Options granted		(1,252,826	)		1,252,826		$	8.48
Options exercised		—			(256,583	)	$	4.68
Options repurchased		10,518			—		$	1.08
Options canceled		367,119			(367,119	)	$	6.58
Balance, December 31, 2020		975,135			2,591,456		$	7.27		8.36
Exercisable as of December 31, 2020					844,226		$	5.79		7.55
Vested and expected to vest as of    December 31, 2020					2,591,456		$	7.27		8.36

Assumptions Used to Calculate Fair Values of Options

The fair values of options were calculated using the assumptions set forth below:

	Year Ended December 31,
	2020	2019	2018
Expected term	5.5 - 6.1 years	5.4 - 6.1 years	5.8 - 6.1 years
Expected volatility	84.9 % - 98.3%	77.2% - 85.5%	80.3% - 82.3%
Risk-free interest rate	0.3% - 1.5%	1.4% - 2.5 %	2.6% - 3.1%
Dividend yield	0%	0%	0%

Summary of Restricted Stock Activity

Restricted stock activity was as follows:

	Number of Shares Underlying Outstanding Restricted Stock Awards		Weighted Average Grant Date Fair Value
Unvested, December 31, 2019		14,625	$	0.82
Vested		—
Unvested, December 31, 2020		14,625	$	0.82