Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Schedule of Total Stock-based Compensation Expense Recognized in Connection with All Share-based Payment Awards

In connection with all stock-based payment awards, total stock-based compensation expense recognized was as follows (in thousands):

	For the Years Ended December 31,
	2023		2022		2021
Cost of sales	$	370	$	226	$	154
Research and development		6,529		14,351		11,842
Selling, general and administrative		14,810		20,822		17,787
Total	$	21,709	$	35,399	$	29,783

Schedule of Stock Based Compensation Expense Recognized by Award Type

The total stock-based compensation expense recognized by award type was as follows (in thousands):

	For the Years Ended December 31,
	2023		2022		2021
Options	$	8,862	$	21,513	$	19,288
RSUs		10,662		12,587		9,348
PSUs		1,222		—		—
ESPP		963		1,299		1,147
Total	$	21,709	$	35,399	$	29,783

Summary of Stock Option Activity for Employees and Nonemployees

	Options			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate  Intrinsic  Value (in thousands)
Options outstanding at December 31, 2022		13,026,359		$	11.46		5.3	$	6
Granted		306,000		$	2.23
Exercised		(13,193	)	$	3.46
Forfeited		(1,120,412	)	$	10.31
Expired		(3,577,944	)	$	12.65
Options outstanding at December 31, 2023		8,620,810		$	10.79		5.3	$	—
Options exercisable at December 31, 2023		6,739,120		$	11.59		4.4	$	—

Summary of RSU Activity

	Number of Shares Underlying RSUs and PSUs			Weighted -Average Grant Date Fair Value
Unvested at December 31, 2022		3,402,825		$	10.35
Granted		7,075,522		$	2.84
Forfeited		(1,761,720	)	$	6.01
Vested		(1,050,201	)	$	10.55
Unvested at December 31, 2023		7,666,426		$	4.40

ESPP [Member]

Schedule of Assumptions Used to Estimate Fair Value on Grant Date Using Black Scholes Option Pricing Model

The fair value of the option component of the shares purchased under the Amended and Restated ESPP was estimated using the Black-Scholes option-pricing model with the following weighted-average assumptions:

	For the Years Ended December 31,
	2023	2022	2021
Volatility	77% - 92%	68% - 131%	58% - 68%
Expected term (in years)	0.5	0.5	0.5
Risk-free interest rate	4.58% - 5.51%	0.06% - 4.58%	0.03% - 0.06%
Dividend	—%	—%	—%

Employee and Nonemployee Stock Option [Member]

Schedule of Assumptions Used to Estimate Fair Value on Grant Date Using Black Scholes Option Pricing Model

The fair value of each stock option granted is estimated on the date of grant using the Black-Scholes option-pricing model. The following table summarizes the assumptions used in calculating the fair value of the stock option awards:

	For the Years Ended December 31,
	2023	2022	2021
Volatility	80%	79%-81%	76%-78%
Expected term (in years)	5.5-5.9	5.5-6.1	5.9-6.1
Risk-free interest rate	3.75%-4.21%	1.69%-4.23%	0.62%-1.35%
Dividend	—%	—%	—%