Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2020

Equity [Abstract]

Schedule of Stock Option Activity

A summary of the Company's stock option activity and related information for the year ended December 31, 2020 is as follows:

	Number of Shares	Weighted Average Exercise Price		Weighted Average Remaining Contractual Life (In Years)	Aggregate Intrinsic Value (In Thousands)
Outstanding at December 31, 2019	5,840,538	$	5.11	7.7	$	45,037
Options granted	2,404,300	11.6
Options exercised	(882,624)	6.42
Options cancelled/forfeited	(515,925)	15.69
Outstanding at December 31, 2020	6,846,289	$	6.42	8.7	$	53,127
Exercisable as of December 31, 2020	1,878,082	$	5.02	7.7	$	17,547

Schedule of Weighted Average Assumptions

The fair value of stock options granted is estimated using the Black-Scholes option pricing model with the following weighted average assumptions:

	December 31,
	2020		2019
Expected volatility	93	%	90	%
Expected dividends	0	%	0	%
Expected terms (years)	6.02		6.07
Risk free rate	0.42	%	1.43	%

Schedule of RSU Activity

A summary of the Company's restricted stock unit activity and related information for the year ended December 31, 2020 is as follows:

	Number of Shares	Weighted Average Grant Date Fair Value
Non-vested at December 31, 2019	72,000	$	3.47
Restricted stock units granted	152,000	9.26
Restricted stock units vested	(36,000)	3.47
Restricted stock units forfeited	(1,500)	3.47
Non-vested at December 31, 2020	186,500	$	8.19

Summary of Stock-based Compensation Expense

Stock-based compensation expense is classified in the consolidated statements of operations as follows (in thousands):

	December 31,
	2020		2019
Research and development expenses	$	1,999	$	486
General and administrative expenses	$	3,623	$	7,197
Total stock-based compensation expense	$	5,622	$	7,683