Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Assumptions Used to Estimate Fair Value of Stock Option Awards Granted

The Company uses the Black-Scholes option pricing model to calculate the fair value of stock options granted.  The fair value of stock options granted was estimated using the following assumptions during the years ended December 31, 2021, 2020 and 2019:

	For the Year Ended December 31,
	2021	2020	2019
Expected volatility	118.75% - 122.17%	120.37% - 121.43%	115.29% - 120.15%
Expected life of option, in years	5.8 - 6.0	5.7 - 6.0	5.3 - 6.0
Risk-free interest rate	1.00% - 1.34%	0.39% - 0.53%	1.58% - 2.64%
Expected dividend yield	0.00%	0.00%	0.00%

Summary of Stock Award Activity for the Period

The following table summarizes the activity related to the stock option awards for the year ended December 31, 2021 (in thousands, except per share amounts):

	Number of Shares			Weighted Average Exercise Price
Awards outstanding at December 31, 2020		4,453,357		$	4.41
Granted		3,368,635			1.43
Exercised		(20,833	)		2.24
Forfeited		(745,124	)		2.60
Awards outstanding at December 31, 2021		7,056,035		$	3.19
Options exercisable at December 31, 2021		2,908,180		$	5.50
Weighted average remaining contractual term	6.3 Years
Options vested and expected to vest at December 31, 2021		5,960,235		$	3.50
Weighted average remaining contractual term	7.9 Years

Summary of Compensation Expense Related to Grants of Stock Options

Compensation expense related to the grants of stock options is included in research and development and general and administrative expense as follows (in thousands):

	2021		2020		2019
Research and development	$	599	$	348	$	522
General and administrative		1,757		661		996
Total share-based compensation expense	$	2,356	$	1,009	$	1,518