Equity Incentive Plans

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Equity Incentive Plans

EQUITY INCENTIVE PLANS

Stock-Based Compensation

Stock-based compensation expense recognized for stock options, restricted stock units ("RSUs"), performance-based restricted stock units ("PRSUs") and our employee stock purchase program (the "ESPP") are recorded as operating expenses in our condensed statements of operations and comprehensive loss, as follows (in thousands):

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Research and development	$	730	$	963	$	2,909	$	3,165
General and administrative	1,532		1,564		5,659		4,984
Total	$	2,262	$	2,527	$	8,568	$	8,149

As of September 30, 2021, our total unrecognized stock-based compensation expense, net of estimated forfeitures, and average remaining vesting period, included the following (dollars in thousands):

	Unrecognized Compensation  Expense		Average Remaining  Vesting Period (Years)
Stock options	$	19,546	2.6
RSUs	$	4,839	3.3
ESPP	$	201	0.4

Stock Options

A summary of our stock option activity and related information for the nine months ended September 30, 2021 is as follows (in thousands, except dollar amounts):

	Number of Shares	Weighted Average Exercise Price
Outstanding balance at December 31, 2020	9,790	$	6.76
Granted	3,410	$	6.60
Exercised	(331)	$	1.96
Forfeited	(1,481)	$	6.01
Outstanding balance at September 30, 2021	11,387	$	6.95
Exercisable at September 30, 2021	6,434	$	7.51

Restricted Stock Units

A summary of our RSUs activity and related information for the nine months ended September 30, 2021 is as follows (in thousands, except dollar amounts):

	Number of RSUs	Weighted Average Value at Grant
Outstanding balance at December 31, 2020	159	$	5.64
Granted	1,124	$	6.62
Vested	(140)	$	6.57
Forfeited	(322)	$	6.68
Unvested at September 30, 2021	820	$	6.42

We issued no PRSUs during the nine months ended September 30, 2021 and we have no PRSUs outstanding as of September 30, 2021.

Employee Stock Purchase Plan

In August 2021, we sold approximately 0.5 million shares of our common stock under the ESPP. The shares were purchased by employees at a purchase price of $1.21 per share resulting in proceeds to us of approximately $0.6 million.

Issuance of Common Stock for Services

Under Our Amended and Restated Non-Employee Director Compensation Program, members of our board of directors may elect to receive shares of our stock in lieu of their cash fees. During the nine months ended September 30, 2021, we issued approximately 25,989 shares of our common stock to members of the board of directors in accordance with the program.