Equity Incentive Plan (Tables)

12 Months Ended

Dec. 31, 2019

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of stock option activity

Stock option activity under the Plan is as follow (in thousands, except share and per share data and years):

	Options Outstanding
				Weighted-
				Average	Aggregate
		Weighted-		Remaining	Intrinsic
	Number	Average		Contractual	Value
	of Shares	Exercise Price		Life (years)	(in thousands)
Balances, December 31, 2017	567,319	$	3.96	8.1	$	694
Granted	1,609,086		6.66
Exercised	(27,832)		1.68
Cancelled	(12,282)		4.92
Balances, December 31, 2018	2,136,291	$	6.06	8.9	$	12,881
Granted	1,764,713		13.63
Exercised	(77,368)		3.94
Cancelled	(81,492)		9.80
Balances, December 31, 2019	3,742,144	$	9.58	8.6	$	22,910
Vested and expected to vest at December 31, 2019	3,742,144	$	9.58	8.6	$	22,910
Exercisable at December 31, 2019	1,793,254	$	5.87	7.7	$	17,211
Vested at December 31, 2019	1,168,118	$	6.27	7.5	$	10,747

Schedule of Share-based Payment Arrangement, Option, Exercise Price Range

	Options Outstanding				Options Exercisable
		Weighted-
		Average				Weighted-
		Remaining	Weighted-			Average
	Number of	Contractual	Average		Shares Subject	Exercise
	Stock Options	Life	Exercise Price		to Stock	Price per
Exercise Prices	Outstanding	(Years)	per Share		Options	Share
Up to $0.66	48,984	2.9	$	0.17	48,984	$	0.17
$4.56-$5.16	1,474,367	7.7	$	5.00	1,450,561	$	5.00
$9.94-$12.95	1,720,981	9.1	$	11.56	293,709	$	11.13
$16.10-$22.06	497,812	9.5	$	17.18	—		—
	3,742,144	8.6	$	9.58	1,793,254	$	5.87

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

	Year Ended December 31,
	2019		2018
Expected life (in years)	6.02		6.01
Volatility	81.0	%	78.3	%
Risk-free interest rate	2.16	%	2.88	%

Schedule of stock-based compensation expense

The compensation expense is allocated on a departmental basis, based on the classification of the option holder as follows (in thousands):

	Year Ended December 31,
	2019		2018
Research and development	$	2,977	$	631
General and administrative		3,079		788
	$	6,056	$	1,419

2019 Employee Stock Purchase Plan

Share-based Compensation Arrangement by Share-based Payment Award [Line Items]

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions

	Year Ended December 31,
	2019		2018
Expected life (in years)	0.2 - 2.0		—
Volatility	74.5 - 101.6	%	—	%
Risk-free interest rate	1.50 - 2.15	%	—	%