Stock-Based Compensation (Tables)

9 Months Ended

Sep. 30, 2024

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Schedule of Stock-Based Compensation Expense

Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows:

	Three Months Ended September 30,				Nine Months Ended September 30,
	2024		2023		2024		2023
	(In thousands)
Research and development	$	24,224	$	21,235	$	69,824	$	60,517
General and administrative		15,395		14,117		44,832		38,490
Total	$	39,619	$	35,352	$	114,656	$	99,007

Summary of Restricted Stock Activity

The following table summarizes the Company’s RSU activity for the nine months ended September 30, 2024:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock units as of December 31, 2023		4,041,753		$	50.40
Granted		3,326,772			33.89
Vested		(1,335,350	)		51.56
Cancelled		(582,581	)		43.50
Unvested restricted stock units as of September 30, 2024		5,450,594		$	40.77

Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted

Weighted average assumptions used to apply this pricing model were as follows:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2024	2023	2024	2023
Risk-free interest rate	4.0%	n/a	4.2%	4.4%
Expected term	6.0 years	n/a	6.0 years	6.0 years
Expected volatility of underlying stock	75.8%	n/a	76.3%	78.7%
Expected dividend yield	0.0%	n/a	0.0%	0.0%

Summary of Stock Option Activity

The following is a summary of stock option activity for the nine months ended September 30, 2024:

	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term		Aggregate Intrinsic Value
						(In years)		(In thousands)
Outstanding at December 31, 2023		5,458,999		$	50.38		6.65	$	35,922
Granted		918,161			30.72
Exercised		(371,736	)		15.69
Forfeited		(526,473	)		71.23
Outstanding at September 30, 2024		5,478,951		$	47.43		6.52	$	11,250
Exercisable at September 30, 2024		4,096,828		$	47.42		5.76	$	11,250

2016 Employee Stock Purchase Plan [Member]

Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]

Summary of Weighted Average Assumptions Used to Compute Fair Value of Option Granted

The fair value of shares under the 2016 Plan was estimated at the beginning of the offering period using a Black-Scholes option-pricing model with the following assumptions:

	Three Months Ended September 30,		Nine Months Ended September 30,
	2024	2023	2024	2023
Risk-free interest rate	5.37%	5.53%	5.24%-5.37%	4.7%-5.53%
Expected term	0.5 years	0.5 years	0.5 years	0.5 years
Expected volatility of underlying stock	59.0%	60.4%	56.7%-59.0%	60.4%-69.2%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%