Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three and nine months ended September 30, 2021 and 2020 were estimated as of the dates of grant using the Black-Scholes option pricing model with the following assumptions:

	Three Months Ended		Nine Months Ended
	September 30,		September 30,
	2021	2020	2021	2020
Risk-free interest rate	0.92% - 1.01%	0.35% - 0.43%	0.66% - 1.23%	0.35% - 1.57%
Expected volatility	83.0% - 83.4%	72.6% - 73.3%	71.6% - 83.5%	72.6% - 74.8%
Expected dividend yield	0%	0%	0%	0%
Expected life of employee and Board options (in years)	6.25	6.25	6.25	6.25

Summary of Compensation Expense Relating to Stock Options

During the three and nine months ended September 30, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows:

	Three Months Ended				Nine Months Ended
	September 30,				September 30,
	2021		2020		2021		2020
Research and development	$	1,833	$	1,724	$	5,228	$	5,003
General and administrative		1,205		1,305		3,444		3,517
Total stock option expense	$	3,038	$	3,029	$	8,672	$	8,520

Summary of Stock Option Activity

A summary of stock option award activity related to employees, non-employee members of the Company’s Board of Directors and non-employee consultants as of and for the nine months ended September 30, 2021 is presented below:

		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2020	5,469,393	$	15.02
Granted	819,250		18.72
Exercised	(114,354)		11.55
Forfeited	(199,506)		17.20
Expired	(234)		18.93
Outstanding, September 30, 2021	5,974,549	$	15.52
Options exercisable, September 30, 2021	3,860,433

Employees And Non-Employee Members Of Board Of Directors [Member]

Summary of Restricted Stock Unit Activity

A summary of restricted stock unit activity related to employees and non-employee members of the Company’s Board of Directors as of and for the nine months ended September 30, 2021 is presented below:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2020	235,250	$	16.25
Awarded	319,200		19.57
Vested and released	(189,421)		17.20
Outstanding, September 30, 2021	365,029	$	18.66
Restricted stock units exercisable (vested and deferred), September 30, 2021	—