Stock-Based Compensation (Tables)

6 Months Ended

Jun. 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 June 30,				Six Months Ended June 30,
	2024		2023		2024		2023
	(In thousands)
Research and development	$	25,439	$	22,351	$	45,600	$	39,282
General and administrative		15,422		14,049		29,437		24,373
Total	$	40,861	$	36,400	$	75,037	$	63,655

Summary of Restricted Stock Activity

The following table summarizes the Company’s RSU activity for the six months ended June 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		3,042,554			34.20
Vested		(1,211,234	)		51.67
Cancelled		(501,576	)		44.28
Unvested restricted stock units as of June 30, 2024		5,371,497		$	41.51

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 June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Risk-free interest rate	4.3%	4.1%	4.2%	4.4%
Expected term	5.6 years	5.6 years	6.0 years	6.0 years
Expected volatility of underlying stock	76.3%	78.8%	76.4%	78.7%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%

Summary of Stock Option Activity

The following is a summary of stock option activity for the six months ended June 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		772,191			31.86
Exercised		(190,246	)		16.49
Forfeited		(331,773	)		77.99
Outstanding at June 30, 2024		5,709,171		$	47.40		6.30	$	15,820
Exercisable at June 30, 2024		4,290,920		$	45.38		5.51	$	15,812

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 June 30,		Six Months Ended June 30,
	2024	2023	2024	2023
Risk-free interest rate	5.24%	4.70%	5.24%	4.70%
Expected term	0.5 years	0.5 years	0.5 years	0.5 years
Expected volatility of underlying stock	56.7%	69.2%	56.7%	69.2%
Expected dividend yield	0.0%	0.0%	0.0%	0.0%