Stock options (Tables)

3 Months Ended

Mar. 31, 2020

Stock options

Schedule of stock option activity

		Weighted-
	Number	Average
	of Shares	Exercise Price
Outstanding at January 1, 2020	4,720,772	$	5.24
Granted	1,412,653		6.10
Exercised	(43,055)		2.77
Cancelled	(41,082)		8.50
Outstanding at March 31, 2020	6,049,288	$	5.44
Exercisable at March 31, 2020	2,846,100	$	4.68

Schedule of restricted stock unit activity

	Number
	of Shares
Unvested at January 1, 2020	447,336
Granted	324,932
Vested	—
Forfeited	(12,075)
Unvested at March 31, 2020	760,193

Schedule of stock-based compensation expense by award type

	Three months ended
	March 31,
		2020		2019
Stock options	$	1,233	$	1,094
Restricted stock units		310		—
Employee stock purchase plan		66		70
Stock-based compensation expense included in Total operating expenses	$	1,609	$	1,164

Schedule of stock-based compensation expense as reflected in the Company’s condensed consolidated statements of operations and comprehensive loss

	Three months ended
	March 31,
		2020		2019
Research and development	$	797	$	516
General and administrative		812		648
Stock-based compensation expense included in Total operating expenses	$	1,609	$	1,164

Schedule of weighted average assumptions for estimating fair value of option awards

	Three months ended
	March 31,
	2020		2019
Risk-free interest rate	1.6	%	2.6	%
Expected dividend yield	—	%	—	%
Expected term (years)	6.04		6.00
Expected stock price volatility	69	%	74	%