Stock-Based Compensation (Tables)

6 Months Ended

Jun. 30, 2021

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three and six months ended June 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		Six Months Ended
	June 30,		June 30,
	2021	2020	2021	2020
Risk-free interest rate	1.07% - 1.23%	0.42% - 0.54%	0.66% - 1.23%	0.42% - 1.57%
Expected volatility	71.78% - 83.48%	73.73% - 74.80%	71.62% - 83.48%	73.72% - 74.80%
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 six months ended June 30, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows:

	Three Months Ended				Six Months Ended
	June 30,				June 30,
	2021		2020		2021		2020
Research and development	$	1,805	$	1,670	$	3,395	$	3,279
General and administrative		1,225		1,142		2,239		2,212
Total stock option expense	$	3,030	$	2,812	$	5,634	$	5,491

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 six months ended June 30, 2021 is presented below:

		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2020	5,469,393	$	15.02
Granted	789,250		18.94
Exercised	(70,529)		13.92
Forfeited	(192,891)		16.99
Outstanding, June 30, 2021	5,995,223	$	15.49
Options exercisable, June 30, 2021	3,636,786

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 six months ended June 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	(145,419)		16.18
Outstanding, June 30, 2021	409,031	$	18.87
Restricted stock units exercisable (vested and deferred), June 30, 2021	—