Stockholders' equity (Tables)

12 Months Ended

Dec. 31, 2021

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, 2021 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, 2020	6,846,289	$	6.42	8.71	$	53,127
Options granted	3,346,049	$	8.70
Options exercised	(124,928)	$	3.28
Options cancelled/forfeited	(1,103,465)	$	7.31
Outstanding at December 31, 2021	8,963,945	$	7.20	8.32	$	6,912
Exercisable as of December 31, 2021	3,665,224	$	5.99	7.45	$	4,729

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,
	2021		2020
Expected volatility	89	%	93	%
Expected dividends	0	%	0	%
Expected terms (years)	6.03		6.02
Risk free rate	0.93	%	0.42	%

Schedule of RSU Activity

A summary of the Company's restricted stock unit activity and related information for the year ended December 31, 2021 is as follows:

	Number of Shares	Weighted Average Grant Date Fair Value
Non-vested at December 31, 2020	186,500	$	8.19
Restricted stock units granted	70,000	$	12.94
Restricted stock units vested	(84,500)	$	7.20
Restricted stock units forfeited	(40,000)	$	12.70
Non-vested at December 31, 2021	132,000	$	9.97

Summary of Stock-based Compensation Expense

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

	December 31,
	2021		2020
Research and development expenses	$	5,095	$	1,999
General and administrative expenses	6,462		3,623
Total stock-based compensation expense	$	11,557	$	5,622