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Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock-based Compensation Expense

Stock-based compensation expense is included in the consolidated statements of operations as follows (in thousands): 

			Year Ended December 31,
			2023						2022						2021
Costs of product revenue			$	354					$	452					$	224
Research and development			2,631						3,907						2,663
Selling, general and administrative			6,986						10,172						8,706
Total			$	9,971					$	14,531					$	11,593

The following table presents total stock-based compensation expense by security type included in the consolidated statements of operations (in thousands):

			Year Ended December 31,
			2023						2022						2021
Stock options			$	3,962					$	4,167					$	2,764
RSUs and RSAs			4,447						4,807						2,768
PSUs			1,649						3,268						2,333
PBOs			(112)						2,289						3,728
ESPP			25						—						—
Total			$	9,971					$	14,531					$	11,593

Assumptions Used to Estimate the Fair Value of Option Grants

The following summarizes the weighted-average assumptions used to estimate the fair value of employee stock options granted:

			Year Ended December 31,
			2023						2022						2021
Expected life (years)			5.8						5.7						5.6
Volatility			66.2		%				62.1		%				52.5		%
Risk-free interest rate			4.0		%				3.1		%				0.8		%
Expected dividend yield			0.0		%				0.0		%				0.0		%

The following summarizes the weighted-average assumptions used to estimate the fair value of 50,000, nil, and 9,000 shares of stock options granted to non-employees for services valued at $0.1 million, nil, and $0.1 million during the years ended December 31, 2023, 2022, and 2021 respectively:

			Year Ended December 31,
			2023						2022						2021
Expected life (years)			5.8						0.0						5.6
Volatility			70.1		%				—		%				54.1		%
Risk-free interest rate			4.7		%				—		%				0.9		%
Expected dividend yield			0.0		%				0.0		%				0.0		%

The following summarize the weighted-average assumptions used to estimate the fair value of PBOs granted:

			Year Ended December 31,
			2022						2021
Expected life (years)			5.6						5.5
Volatility			54.9		%				51.9		%
Risk-free interest rate			1.8		%				0.7		%
Expected dividend yield			0.0		%				0.0		%

Schedule of Share-based Compensation, Stock Options, Activity

The following tables summarizes stock option activities:

			Number of Shares						Weighted Average Exercise Price Per Share
			(In Thousands)
Outstanding at December 31, 2020			3,385						$	7.19
Granted			286						$	26.85
Exercised			(664)						$	6.96
Forfeited/Expired			(72)						$	17.99
Outstanding at December 31, 2021			2,935						$	8.90
Granted			2,000						$	8.90
Exercised			(410)						$	2.33
Forfeited/Expired			(275)						$	19.01
Outstanding at December 31, 2022			4,250						$	8.88
Granted			2,046						$	5.23
Exercised			(283)						$	1.97
Forfeited/Expired			(839)						$	12.08
Outstanding at December 31, 2023			5,174						$	7.31

			Number of Shares						Weighted Average Exercise Price Per Share						Weighted Average Remaining Contractual Term						Aggregate Intrinsic Value
			(In Thousands)												(In Years)						(In Thousands)
Outstanding at December 31, 2023			5,174						$	7.31					6.7						$	198
Exercisable at December 31, 2023			2,231						$	8.61					3.6						$	79
Vested and expected to vest at December 31, 2023			4,748						$	7.42					6.4						$	170

Schedule of Share-based Compensation, RSA Activity

The following table summarizes RSA activities:

			Number of Shares						Weighted Average Grant Date Fair Value Per Share
			(In Thousands)
Non-vested balance at December 31, 2020			96						$	11.44
Granted			46						$	21.91
Vested			(62)						$	11.31
Non-vested balance at December 31, 2021			80						$	17.53
Granted			159						$	7.53
Vested			(58)						$	18.42
Non-vested balance at December 31, 2022			181						$	8.45
Granted			277						$	2.89
Vested			(133)						$	9.04
Non-vested balance at December 31, 2023			325						$	3.48

Schedule of Share-based Compensation, RSU Activity

The following table summarizes RSU activities:

			Number of Shares						Weighted Average Grant Date Fair Value Per Share
			(In Thousands)
Non-vested balance at December 31, 2020			176						$	14.17
Granted			163						$	26.59
Vested			(70)						$	13.57
Forfeited/Expired			(37)						$	21.89
Non-vested balance at December 31, 2021			232						$	21.83
Granted			518						$	17.46
Vested			(106)						$	21.21
Forfeited/Expired			(126)						$	19.55
Non-vested balance at December 31, 2022			518						$	18.15
Granted			1,049						$	5.24
Vested			(204)						$	18.42
Forfeited/Expired			(343)						$	9.71
Non-vested balance at December 31, 2023			1,020						$	7.66

Share-based Compensation, Performance Shares Award Outstanding Activity

The following table summarizes PSU activities:

			Number of Shares						Weighted Average Grant Date Fair Value Per Share
			(In Thousands)
Non-vested balance at December 31, 2020			131						$	15.34
Granted			82						$	26.16
Vested			(66)						$	16.14
Forfeited/Expired			(19)						$	19.38
Non-vested balance at December 31, 2021			128						$	21.24
Granted			686						$	9.55
Vested			(107)						$	20.52
Forfeited/Expired			(40)						$	19.93
Non-vested balance at December 31, 2022			667						$	9.41
Vested			(315)						$	11.02
Forfeited/Expired			(75)						$	12.49
Other			15						$	25.05
Non-vested balance at December 31, 2023			292						$	7.69

The following tables summarizes PBOs activities:

			Number of Shares						Weighted Average Grant Date Fair Value Per Share
			(In Thousands)
Outstanding at December 31, 2020			1,560						$	5.05
Granted			433						$	12.23
Exercised			(35)						$	9.02
Forfeited/Expired			(118)						$	12.23
Outstanding at December 31, 2021			1,840						$	4.11
Granted			733						$	9.89
Forfeited/Expired			(747)						$	8.29
Outstanding at December 31, 2022			1,826						$	4.70
Forfeited/Expired			(178)						$	9.73
Outstanding at December 31, 2023			1,648						$	5.64

			Number of Shares						Weighted Average Exercise Price Per Share						Weighted Average Remaining Contractual Term						Aggregate Intrinsic Value
			(In Thousands)												(In Years)						(In Thousands)
Exercisable at December 31, 2023			1,627						$	10.96					4.4						$	—
Vested and expected to vest at December 31, 2023			1,646						$	11.06					4.5						$	—

Schedule of Share-Based Payment Award, Employee Stock Purchase Plan, Valuation Assumptions

The fair value of shares to be issued under the ESPP is computed using the Black-Scholes-Merton option pricing model at the commencement of the offering period. The following summarizes the weighted-average assumptions used to estimate the fair value of ESPP for the initial offering period:

			Year Ended December 31,
			2023
Expected life (years)			0.4
Volatility			89.6		%
Risk-free interest rate			5.3		%
Expected dividend yield			0.0		%

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