Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2020

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Pre-funded Warrants for Common Stock Issued and Outstanding

As of September 30, 2020, the following pre-funded warrants for common stock were issued and outstanding:

Issue Date	Expiration Date	Exercise Price		Number of Warrants Outstanding
February 8, 2019	None	$	0.0001		4,000,000
April 30, 2020	None	$	0.0001		13,610,328
Total pre-funded warrants					17,610,328

Schedule of Company’s Stock Awards Granted

The following table summarizes the Company’s stock awards granted for each of the periods indicated:

	Three Months Ended September 30,								Nine Months Ended September 30,
	2020				2019				2020				2019
	Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value		Grants		Weighted Average Grant Date Fair Value
Stock options		409,500	$	2.45		44,000	$	5.64		1,853,900	$	4.61		1,245,900	$	5.72
Restricted stock units		228,200	$	8.13		—	$	—		228,200	$	8.13		—	$	—

Summary of Stock-Based Compensation Expense

Total stock-based compensation expense related to the Company’s equity incentive plans and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2020		2019		2020		2019
Research and development	$	454	$	492	$	1,651	$	1,358
General and administrative		1,242		874		2,993		2,334
Total stock-based compensation expense	$	1,696	$	1,366	$	4,644	$	3,692

Schedule of Estimated Fair Value of Stock Options Granted

The following table summarizes the weighted-average Black-Scholes option pricing model assumptions used to estimate the fair value of stock options granted under the Company’s equity incentive plans, and the shares purchasable under the 2016 ESPP during the periods presented:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2020			2019			2020			2019
Equity Incentive Plans
Expected term (in years)		6.72			6.08			6.11			5.99
Expected volatility		82	%		80	%		76	%		81	%
Risk-free interest		0.44	%		1.63	%		1.10	%		2.47	%
Dividend yield		0	%		0	%		0	%		0	%
2016 ESPP
Expected term (in years)		0.50			0.50			0.50			0.50
Expected volatility		96	%		74	%		76	%		70	%
Risk-free interest		0.13	%		1.71	%		0.75	%		2.12	%
Dividend yield		0	%		0	%		0	%		0	%