Equity-based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

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 income (loss) is as follows (in thousands):

	Years Ended December 31,
	2021		2020		2019
Research and development	$	59,683	$	35,120	$	23,273
General and administrative		42,707		30,898		20,784
Loss from equity method investment		—		—		5,467
Total	$	102,390	$	66,018	$	49,524

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,
	2021			2020			2019
Options granted		1,616,255			2,182,773			2,832,784
Weighted-average exercise price	$	124.32		$	68.91		$	39.16
Weighted-average grant date fair value	$	77.38		$	42.28		$	24.57
Assumptions:
Expected volatility		70.3	%		69.2	%		68.9	%
Expected term (in years)		6.0			6.0			6.0
Risk-free interest rate		1.0	%		0.6	%		2.2	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

Summary of Stock Option Activity

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

	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		8,101,980		$	42.44		7.8	$	896,666
Granted		1,616,255		$	124.32
Exercised		(1,245,071	)	$	30.96
Cancelled or forfeited		(660,182	)	$	79.54
Outstanding at December 31, 2021		7,812,982		$	58.07		7.4		219,103
Exercisable at December 31, 2021		4,598,353		$	40.86		6.6	$	174,056
Vested and expected to vest at December 31, 2021		7,812,982		$	58.07		7.4	$	219,103

Summary of Restricted Stock Activity

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

	Shares			Weighted- Average Grant Date Fair Value
Unvested balance at December 31, 2020		894,092		$	70.55
Granted		628,175			111.73
Vested		(455,440	)		58.00
Cancelled or forfeited		(132,652	)		100.25
Unvested balance at December 31, 2021		934,175		$	100.14