Common Stock and Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Share-based Payment Arrangement [Abstract]

Summary of stock options, RSU and PSU activity

A summary of stock option, RSU and PSU activity under the 2014 Plan during the nine months ended September 30, 2021 and 2020 is presented below:

	Stock Options	RSUs	PSUs
Outstanding at December 31, 2019	3,096,161	251,215	116,181
Granted	662,700	231,450	—
Options exercised/RSUs vested/PSUs vested	(41,951)	(67,970)	—
Forfeited or expired	(185,615)	(53,824)	(11,431)
Outstanding at September 30, 2020	3,531,295	360,871	104,750
Outstanding at December 31, 2020	3,331,890	328,396	97,750
Granted	109,000	106,600	159,000
Options exercised/RSUs vested/PSUs vested	(100,477)	(94,273)	—
Forfeited or expired	(308,815)	(46,941)	(97,750)
Outstanding at September 30, 2021	3,031,598	293,782	159,000

Fair value of stock options

The fair value of stock options granted to employees, directors, and consultants were estimated using the following assumptions:

	Three Months Ended September 30,		Nine Months Ended   September 30,
	2021	2020	2021	2020
Risk-free interest rate	0.82% - 0.93%	0.37% - 0.41%	0.51% - 1.12%	0.37% - 1.65%
Volatility	54.92%	55.42%	56.07%	54.98%
Expected term (in years)	6.08 years	6.07 years	5.68 years	6.03 years
Expected dividend yield	0.0%	0.0%	0.0%	0.0%

Share-based payment arrangement, cost by plan

We recognized stock-based compensation in our condensed consolidated statements of operations for the three and nine months ended September 30, 2021 and 2020 as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2021		2020		2021		2020
Stock options	$	2,515	$	3,685	$	8,393	$	12,831
RSUs	1,046		928		4,051		4,115
PSUs	523		109		2,429		1,489
Stock-based compensation expense	$	4,084	$	4,722	$	14,873	$	18,435
Selling, general and administrative	$	3,443	$	5,236	$	12,696	$	16,365
Research and development	641		(514)		2,177		2,070
Stock-based compensation expense	$	4,084	$	4,722	$	14,873	$	18,435