Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2018

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, 2018 Plan, and 2016 ESPP was as follows (in thousands):

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2018		2017		2018		2017
Research and development	$	377	$	277	$	1,090	$	672
General and administrative		695		451		1,813		1,122
Total stock-based compensation expense	$	1,072	$	728	$	2,903	$	1,794

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 2016 Plan and 2018 Plan, and the shares purchasable under the 2016 ESPP during the periods presented:

	Three Months Ended						Nine Months Ended
	September 30,						September 30,
	2018			2017			2018			2017
2016 Plan and 2018 Plan
Expected term (in years)		6.00			5.82			5.96			5.91
Expected volatility		84	%		85	%		85	%		86	%
Risk-free interest		2.80	%		1.88	%		2.75	%		1.99	%
Dividend yield		0	%		0	%		0	%		0	%
2016 ESPP
Expected term (in years)		0.50			0.50			0.49			0.50
Expected volatility		63	%		79	%		66	%		79	%
Risk-free interest		2.45	%		1.23	%		2.20	%		0.90	%
Dividend yield		0	%		0	%		0	%		0	%