Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

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 consolidated statements of operations and comprehensive loss as follows:

	Year Ended December 31,
	2023		2022		2021
	(In thousands)
Research and development	$	82,211	$	56,279	$	26,712
General and administrative		51,839		35,121		20,297
Total	$	134,050	$	91,400	$	47,009

Summary of Restricted Stock Activity

The following table summarizes the Company’s RSU activity for the year ended December 31, 2023:

	Number of Shares			Weighted Average Grant Date Fair Value per Share
Unvested restricted stock units as of December 31, 2022		1,941,379		$	70.70
Granted		3,047,544			41.30
Vested		(677,055	)		68.04
Cancelled		(270,115	)		49.41
Unvested restricted stock units as of December 31, 2023		4,041,753		$	50.40

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:

	Year Ended December 31,
	2023			2022			2021
Risk-free interest rate		4.4	%		1.9	%		1.0	%
Expected life of options	6.0 years			5.9 years			6.0 years
Expected volatility of underlying stock		78.7	%		76.2	%		72.9	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

The following is a summary of stock option activity for the year ended December 31, 2023:

	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, 2022		5,471,675		$	49.86
Granted		569,821			41.00
Exercised		(385,130	)		17.13
Forfeited		(197,367	)		73.90
Outstanding at December 31, 2023		5,458,999		$	50.38		6.65	$	35,922
Exercisable at December 31, 2023		4,017,227		$	43.63		6.14	$	34,790

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 the awards issued under the 2016 Plan to employees was estimated at the beginning of the offering period using a Black-Scholes option-pricing model with the following assumptions:

	Year Ended December 31,
	2023			2022			2021
Risk-free interest rate	4.7%-5.53%			0.22%-2.52%			0.05%-0.09%
Expected term (in years)	0.5 years			0.5 years			0.5 years
Expected volatility of underlying stock	60.4%-69.2%			63.6%-95.3%			77.5%-109.2%
Expected dividend yield		0.0	%		0.0	%		0.0	%