Stock-based compensation (Tables)

12 Months Ended

Dec. 31, 2019

Stock-based compensation

Schedule of assumptions used in the Black-Scholes option-pricing model for estimating the fair value of stock options

	Year ended December 31,
	2019		2018		2017
Risk-free interest rate	2.21	%	2.78	%	(0.67)	%
Expected term (in years)	6.1		5.1		2.8
Expected volatility	74.2	%	72.1	%	66.1	%
Expected dividends	—	%	—	%	—	%

Schedule of summary of stock option activity

The following table summarizes the Company’s stock option activity since January 1, 2019 (in thousands, except share and per share amounts):

				Weighted
		Weighted		Average
		Average		Remaining	Aggregate
	Number of	Exercise		Contractual	Intrinsic
	Shares	Price		Term	Value
				(in years)
Outstanding as of December 31, 2018	1,606,325	$	1.95	8.0	$	13,466
Granted	1,661,200		12.34
Exercised	(157,636)		0.10
Forfeited	(110,605)		6.72
Outstanding as of December 31, 2019	2,999,284	$	7.63	8.1	$	15,840
Options exercisable as of December 31, 2019	836,105	$	0.88	6.1	$	9,488
Options unvested as of December 31, 2019	2,163,179	$	10.23	8.9	$	6,352

Schedule of stock-based compensation expense

Stock-based compensation expense was classified in the consolidated statements of operations and comprehensive loss as follows (in thousands):

	Year ended December 31,
	2019		2018		2017
Research and development expenses	$	1,981	$	399	$	295
General and administrative expenses		3,584		468		475
	$	5,565	$	867	$	770