Stock Based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Option Activity Under Company's Equity Incentive Plans

The following table summarizes stock option activity under the Company’s equity incentive plans and related information:

	Number of Shares Underlying Outstanding Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)
Outstanding — December 31, 2020		2,355,615		$	8.59		7.96
Options granted		939,613		$	6.21
Options exercised		—		$	—
Options forfeited		(87,083	)	$	7.62
Options expired		—		$	—
Outstanding — March 31, 2021		3,208,145		$	7.92		8.37
Exercisable — March 31, 2021		1,213,061		$	10.18

Summary of Weighted Average Valuation Assumptions Used to Estimate Fair Value of Employee Stock Options

The fair value of employee stock options was estimated using the following weighted-average assumptions for the three months ended March 31, 2021 and 2020:

	Three Months Ended March 31,
	2021			2020
Employee Stock Options:
Risk-free interest rate		0.69	%		1.57	%
Expected term (in years)		6.05			5.53
Dividend yield		—			—
Volatility		93.83	%		110.00	%
Weighted-average fair value of stock options granted	$	4.70		$	5.58

Summary of Stock-Based Compensation Recognized

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

	Three Months Ended March 31,
	2021		2020
Research and development	$	369	$	344
General and administrative(1)		657		461
Total stock-based compensation	$	1,026	$	805

(1) Included in general and administrative stock-based compensation for the three months ended March 31, 2021 is expense related to 10,149 shares of common stock issued to certain board members in lieu of their cash compensation.