Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

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, 2020, 2019 and 2018:

	For the Year Ended December 31,
	2020	2019	2018
Expected volatility	120.37% - 121.43%	115.29% - 120.15%	71.15% - 99.23%
Expected life of option, in years	5.7 - 6.0	5.3 - 6.0	5.7 - 6.0
Risk-free interest rate	0.39% - 0.53%	1.58% - 2.64%	2.69% - 2.84%
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, 2020 (in thousands, except per share amounts):

	Number of Shares			Weighted- Average Exercise Price
Awards outstanding at December 31, 2019		2,531,143		$	6.19
Granted		1,975,250			2.10
Forfeited		(53,036	)		3.28
Awards outstanding at December 31, 2020		4,453,357		$	4.41
Options exercisable at December 31, 2020		1,852,721		$	7.58
Weighted average remaining contractual term	6.0 Years
Options vested and expected to vest at December 31, 2020		4,166,666		$	4.57
Weighted average remaining contractual term	7.9 Years

Summary of Activity Related to Awards of RSUs

The following table summarizes the activity related to the awards of RSUs for the year ended December 31, 2020:

	Number of Shares			Weighted- Average Grant Date Fair Value
Awards outstanding at December 31, 2019		11,667		$	5.81
Vested		(11,667	)		5.81
Awards outstanding at December 31, 2020		—		$	—
RSUs expected to vest at December 31, 2020		—		$	—

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):

	2020		2019		2018
Research and development	$	348	$	522	$	994
General and administrative		661		996		1,682
Total share-based compensation expense	$	1,009	$	1,518	$	2,676