Stock-Based Compensation Expense (Tables)

12 Months Ended

Dec. 31, 2023

Effect of Recording Stock-Based Compensation Expense

The effect of recording stock-based compensation (“SBC”) expense for the years ended December 31, 2023, 2022 and 2021 is as follows (in thousands):

	Years Ended December 31,
	2023		2022		2021
Research and development	$	2,911	$	1,644	$	1,895
Selling, general and administrative		15,146		21,201		23,733
Total stock-based compensation expense	$	18,057	$	22,845	$	25,628

Employee Stock Purchase Plan

Schedule of Assumptions Used to Value Awards Granted

The following assumptions were used to value the ESPP shares:

	Years Ended December 31,
	2023		2022		2021
Expected life (years)		2.0		2.0		2.0
Risk-free interest rate	4.3% − 4.6%		1.3 − 4.3%		0.1 − 0.2%
Dividend yield	2.0%		1.1 − 2.3%		0.9 − 1.2%
Expected volatility	61.3% − 63.5%		48.5 − 69.0%		52.0%

Performance Stock Units

Schedule of Assumptions Used to Value Awards Granted

The following assumptions were used to value the performance stock awards subject to market conditions granted in the years ended December 31, 2023, 2022 and 2021:

	Years Ended December 31,
	2023	2022	2021
Expected life (in years)	2.4 − 3.0	3.0	3.0
Risk-free interest rate	3.64% − 4.85%	2.8%	0.3%
Dividend yield	1.91% − 2.32%	1.2%	1.0%
Expected volatility	61.3% − 68.5%	37.5% − 40.9%	47.9%