Stockholders' Equity (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

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				Six Months Ended
	June 30,				June 30,
	2019		2018		2019		2018
Research and development	$	464	$	390	$	866	$	713
General and administrative		781		606		1,460		1,118
Total stock-based compensation expense	$	1,245	$	996	$	2,326	$	1,831

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						Six Months Ended
	June 30,						June 30,
	2019			2018			2019			2018
Equity Incentive Plans
Expected term (in years)		5.70			5.70			5.99			5.95
Expected volatility		78	%		84	%		81	%		85	%
Risk-free interest		2.05	%		2.79	%		2.50	%		2.73	%
Dividend yield		0	%		0	%		0	%		0	%
2016 ESPP
Expected term (in years)		—			—			0.49			0.49
Expected volatility		—			—			66	%		69	%
Risk-free interest		—			—			2.55	%		2.00	%
Dividend yield		—			—			0	%		0	%