Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Share-Based Payment Arrangement [Abstract]

Schedule of Stock-Based Compensation Expense

Stock‑based compensation expense by classification within the consolidated statements of operations and comprehensive (loss) income is as follows (in thousands):

	Years Ended December 31,
	2023		2022		2021
Research and development	$	46,356	$	53,956	$	59,683
General and administrative		34,672		43,991		42,707
Total	$	81,028	$	97,947	$	102,390

Fair Value of Each Option Issued to Employees Estimated Using Black-Scholes Option-Pricing Model

The fair value of each option issued to employees was estimated at the date of grant using the Black-Scholes option pricing model with the following weighted-average assumptions:

	Years Ended December 31,
	2023			2022			2021
Options granted		1,860,485			1,492,589			1,616,255
Weighted-average exercise price	$	45.47		$	60.19		$	124.32
Weighted-average grant date fair value	$	28.39		$	38.54		$	77.38
Assumptions:
Expected volatility		65.1	%		70.2	%		70.3	%
Expected term (in years)		6.0			6.0			6.0
Risk-free interest rate		4.1	%		2.6	%		1.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

The following table summarizes stock option activity under the Company’s equity award plans (intrinsic value in thousands):

Summary of Stock Option Activity

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2022		7,230,233		$	60.22		7.0	$	32,131
Granted		1,860,485			45.47
Exercised		(742,291	)		38.53
Cancelled or forfeited		(1,144,055	)		82.84
Outstanding at December 31, 2023		7,204,372		$	55.05		6.7	$	115,681
Exercisable at December 31, 2023		4,861,029		$	53.73		5.7	$	88,206
Vested and expected to vest at December 31, 2023		7,204,372		$	55.05		6.7	$	115,681

The total intrinsic value (the amount by which the fair market value exceeded the exercise price) of stock options exercised during the year ended December 31, 2023, 2022 and 2021 was $13.9 million, $40.8 million, and $119.5 million, respectively.

Summary of Restricted Stock Activity

The following table summarizes the restricted stock unit activity under the Company’s equity award plans:

	Shares			Weighted- Average Grant Date Fair Value
Unvested balance at December 31, 2022		1,325,185		$	80.13
Granted		1,078,114			49.52
Vested		(277,808	)		96.23
Cancelled or forfeited		(344,076	)		70.29
Unvested balance at December 31, 2023		1,781,415		$	61.00