Stock-Based Compensation (Tables)

3 Months Ended

Mar. 31, 2021

Summary of Assumptions Used in Black-Scholes Option Pricing Model

The fair values of stock options granted during the three months ended March 31, 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
	March 31,
	2021	2020
Risk-free interest rate	0.66% - 1.21%	0.54% - 1.57%
Expected volatility	71.62% - 71.84%	73.72% - 74.71%
Expected dividend yield	0%	0%
Expected life of employee and Board options (in years)	6.25	6.25

Summary of Compensation Expense Relating to Stock Options

During the three months ended March 31, 2021 and 2020, the Company recognized compensation expense relating to stock options as follows:

	Three Months Ended
	March 31,
	2021		2020
Research and development	$	1,590	$	1,609
General and administrative		1,014		1,070
Total stock option expense	$	2,604	$	2,679

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 three months ended March 31, 2021 is presented below:

		Weighted
	Number of	Average Exercise
	Shares	Price
Outstanding, December 31, 2020	5,469,393	$	15.02
Granted	673,200		19.47
Exercised	(45,035)		15.29
Forfeited	(178,750)		17.30
Outstanding, March 31, 2021	5,918,808	$	15.46
Options exercisable, March 31, 2021	3,375,272

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 three months ended March 31, 2021 is presented below:

		Weighted
	Number of	Average Grant
	Units	Date Fair Value
Outstanding, December 31, 2020	235,250	$	16.25
Awarded	276,000		20.59
Vested and released	(109,419)		16.36
Outstanding, March 31, 2021	401,831	$	19.20
Restricted stock units exercisable (vested and deferred), March 31, 2021	—