Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2021

The following table summarizes stock option activity under the Company’s stock-based compensation plans during the year ended December 31, 2021 (in thousands, except option and share data):

	Shares Available for Grant			Number of Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Life (in Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		1,021,109			3,697,075		$	10.81		7.55	$	9,048
Additional options authorized		2,543,924			—
Granted		(1,866,785	)		1,866,785		$	8.92
Restricted stock units granted		(371,500	)		—
Performance stock units granted		(270,000	)		—
Exercised		—			(53,028	)	$	6.81
Forfeited or cancelled		248,647			(248,647	)	$	9.52
Restricted stock units forfeited		22,250			—		$	—
Outstanding as of December 31, 2021		1,327,645			5,262,185		$	10.24		7.25	$	530
Vested and exercisable as of December 31, 2021					2,983,332		$	11.20		6.11	$	482

Summary of Non-cash Stock Based Compensation Expense

Total stock-based compensation expense recognized was as follows (in thousands):

	Year Ended December 31,
	2021		2020		2019
Research and development	$	2,252	$	1,494	$	1,550
Selling, general and administrative		5,649		4,479		4,129
Total	$	7,901	$	5,973	$	5,679

Employees and Non Employees Stock Option [Member]

Weighted-average assumptions used in Black-Scholes Model to estimate fair value of stock options granted

The fair value of stock options was estimated using the following weighted-average assumptions:

	Year Ended December 31,
	2021		2020		2019
Expected term (in years)	5.27 - 6.08		5.00 - 6.08		5.27 - 6.08
Contractual term (in years)		—		10.00		10.00
Volatility	68.96% - 71.40%		73.00% - 77.00%		73.14% - 83.19%
Risk free interest rate	0.62% - 1.35%		0.39% - 1.37%		1.42% - 2.57%
Dividend yield		—		—		—