Stock-Based Compensation and Equity Plans (Tables)

12 Months Ended

Dec. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock Option Activity

The following table summarizes stock option activity for the year ended December 31, 2021 (in thousands except per share amounts and years):

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (In Years)		Aggregate Intrinsic Value
Outstanding as of December 31, 2020		9,843		$	4.11
Granted		2,965		$	4.26
Exercised		(3	)	$	2.11
Forfeited		(1,097	)	$	4.10
Outstanding as of December 31, 2021		11,708		$	4.15		6.8	$	460
Options vested and expected to vest as of    December 31, 2021		11,708		$	4.15		6.8	$	460
Options exercisable as of December 31, 2021		6,994		$	4.44		5.6	$	348

Summary of Certain Information Regarding Stock Options

The following table summarizes certain information regarding stock options (in thousands, except per share data):

	Years Ended December 31,
	2021		2020		2019
Weighted-average grant-date fair value per share of    options granted during the period	$	3.32	$	2.68	$	1.64
Cash received from options exercised during the    period		6		206		5
Intrinsic value of options exercised during the period		1		59		2

Summary of Restricted Stock Unit, Activity

The following table summarizes restricted stock unit activity for the year ended December 31, 2021 (share amounts in thousands):

	Restricted Stock Units			Weighted-Average Grant-Date Fair Value
Unvested as of December 31, 2020		—		$	—
Granted		1,697		$	2.16
Vested		—		$	—
Forfeited		(47	)	$	2.16
Unvested as of December 31, 2021		1,650		$	2.16

Weighted-Average Underlying Assumptions Used to Determine Fair Value of Stock Options and ESPP Rights

The following are the weighted-average underlying assumptions used to determine the fair value of stock options and ESPP rights using the Black-Scholes-Merton option pricing model:

	Years Ended December 31,
	2021			2020			2019
Stock Options:
Risk-free interest rate		0.8	%		1.5	%		2.5	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected volatility		99.2	%		96.7	%		98.1	%
Expected term (in years)		6.0			6.1			6.1
Employee Stock Purchase Plan:
Risk-free interest rate		0.1	%		0.1	%		2.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%
Expected volatility		90.9	%		69.8	%		69.5	%
Expected term (in years)		1.3			1.3			1.3

Summary of Non-cash Stock Based Compensation Expense

Total non-cash stock-based compensation expense recognized in the statements of operations is as follows (in thousands):

	Years Ended December 31,
	2021		2020		2019
Cost of product sales	$	3	$	13	$	12
Research and development		3,355		2,456		2,085
Selling, general and administrative		4,039		3,642		2,793
Total stock-based compensation	$	7,397	$	6,111	$	4,890