Equity (Tables)

6 Months Ended

Jun. 30, 2021

Equity [Abstract]

Summary of Stock-based Compensation Expense

Stock-based compensation expense is classified in the condensed consolidated statement of operations as follows:

(in thousands)	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Research and development expenses	$	1,409	$	346	$	2,427	$	629
General and administrative expenses	1,509		676		2,911		1,076
Total stock-based compensation expense	$	2,918	$	1,022	$	5,338	$	1,705

Schedule of Weighted Average Assumptions

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2021		2020		2021		2020
Expected volatility	89.12	%	93.61	%	89.19	%	92.09	%
Expected dividends	0	%	0	%	0	%	0	%
Expected terms (years)	5.94		5.82		5.95		5.91
Risk free rate	1.07	%	0.41	%	1.00	%	0.56	%

Schedule of Stock Options Activity

A summary of the Company’s stock option activity and related information for the six months ended June 30, 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	1,050,300	$	12.29
Options exercised	(116,861)	$	3.21
Options cancelled/forfeited	(73,375)	$	11.25
Outstanding at June 30, 2021	7,706,353	$	7.22	8.43	$	26,289
Exercisable as of June 30, 2021	2,487,966	$	5.14	7.57	$	12,422

Summary of RSU Activity

A summary of the Company’s RSU activity and related information for the six months ended June 30, 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	(83,000)	$	7.27
Restricted stock units forfeited	—	$	—
Non-vested at June 30, 2021	173,500	$	10.54