Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Information Regarding Stock Options Outstanding Stock Options Vested and Expected to Vest and Stock Options Exercisable

Information regarding the Company’s stock options outstanding, stock options vested and expected to vest, and stock options exercisable at December 31, 2023, was as follows (in thousands except weighted average exercise price and contractual term):

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value
Balances at December 31, 2023
Stock options outstanding		14,515	$	5.20		4.14		—
Stock options vested and expected to vest		14,495		5.20		4.14		—
Stock options exercisable		13,162		5.13		3.78		—

Recognition of Stock-Based Compensation Expense

Stock-based compensation expense recognized on the Company’s consolidated statements of operations for the years ended December 31, 2023, 2022 and 2021, was as follows (in thousands):

	Year Ended December 31,
	2023		2022		2021
Research and development	$	5,823	$	5,635	$	4,950
Selling, general and administrative		14,448		18,821		18,621
Total stock-based compensation expense	$	20,271	$	24,456	$	23,571

Weighted Average Assumptions Used to Value Stock-Based Awards

The weighted average assumptions used to value the Company’s stock-based awards for the years ended December 31, 2023, 2022 and 2021, was as follows:

	Year Ended December 31,
	2023			2022			2021
Stock Options:
Expected term (in years)		—			6.82			6.97
Estimated volatility		—			55	%		55	%
Risk-free interest rate		—			1.89	%		1.16	%
Expected dividend yield		—			0	%		0	%
Employee Stock Purchase Plan Rights:
Expected term (in years)		0.75			0.74			0.74
Estimated volatility		70	%		56	%		56	%
Risk-free interest rate		5.29	%		2.25	%		0.07	%
Expected dividend yield		0	%		0	%		0	%

2008 Equity Incentive Plan

Activity Under Equity Incentive Plans Related to Stock Options

Activity under the Company’s equity incentive plans related to stock options is set forth below (in thousands except per share amounts):

	Number of Options Outstanding			Weighted Average Exercise Price per Share
Balance at December 31, 2022		15,756		$	5.12
Granted		—			—
Exercised		—			—
Forfeited/canceled		(1,241	)		4.20
Balance at December 31, 2023		14,515			5.20

Activity Under Equity Incentive Plans Related to RSUs

Activity under the Company’s equity incentive plans related to RSUs is set forth below (in thousands except per share amounts):

	Number of RSUs Unvested			Weighted Average Grant Date Fair Value per Share
Balance at December 31, 2022		8,497		$	5.76
Granted (1)		7,264			2.64
Vested (1)		(3,194	)		5.66
Forfeited (1)		(1,881	)		5.39
Balance at December 31, 2023		10,686			3.74

(1) Includes shares issuable under performance-based restricted stock unit awards.