Equity Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2019

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activity under 2015 Plan and 2018 Plan

Stock option activity during the six months ended June 30, 2019 under both of the 2015 Plan and the 2018 Plan is as follows:

				Weighted-		Weighted-		Aggregate
				Average		Average		Intrinsic
	Options			Exercise		Remaining		Value
	Outstanding			Price		Term		(000’s)
Balance at December 31, 2018		2,339,157		$	6.40
Granted		773,125		$	24.84
Cancelled		(9,119	)	$	9.28
Exercised		(63,014	)	$	1.39
Balance at June 30, 2019		3,040,149		$	11.18		8.8	$	42,418
Exercisable at June 30, 2019		776,012		$	5.39		8.2	$	15,224

Weighted Average Assumptions Used to Estimate Fair Value of Stock Options Granted to Employees

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

Stock Option Plans	2019	2018
Expected life of option	5.9 years	6.0 years
Volatility	78%	70%
Risk free interest rate	2.4%	2.8%
Dividend yield	—%	—%

Employee Stock Purchase Plan	2019	2018
Expected life of option	1.3 years	N/A
Volatility	62%	N/A
Risk free interest rate	2.3%	N/A
Dividend yield	—%	N/A

Summary of Stock-based Compensation Expense for the Equity Awards Issued to Employees and Non-Employees

Stock-based compensation expense for the equity awards issued by the Company to employees and non-employees for the periods presented below was as follows (in thousands):

	Three months ended June 30,				Six months ended June 30,
	2019		2018		2019		2018
Included in research and development	$	839	$	130	$	1,378	$	291
Included in general and administrative		742		141		1,231		407
Total	$	1,581	$	271	$	2,609	$	698