Income Taxes (Tables)

12 Months Ended

Dec. 31, 2022

Income Tax Disclosure [Abstract]

Summary of Income (Loss) Before Income Tax Expense

Income (loss) before income tax expense consists of the following:

	Year Ended December 31,
	2022			2021			2020
	(in thousands)
Domestic	$	(532,539	)	$	(457,693	)	$	639,986
Foreign		(245	)		(199	)		(33,913	)
	$	(532,784	)	$	(457,892	)	$	606,073

Summary of Reconciliation of U.S. Statutory Rate to Company's Effective Tax Rate

A reconciliation of the U.S. statutory rate to the Company’s effective tax rate is as follows:

	Year Ended December 31,
	2022			2021			2020
Tax due at statutory rate		21.0	%		21.0	%		21.0	%
State taxes, net of federal		1.8			1.9			5.7
Biogen transaction-related items		—			—			(10.1	)
Stock-based compensation		(1.9	)		(5.2	)		0.9
Foreign rate differential		—			—			1.2
Federal and state tax credits		2.1			3.5			(1.5	)
Change in valuation allowance		(23.0	)		(20.7	)		(17.6	)
Other		—			(0.5	)		0.4
		0.0	%		0.0	%		0.0	%

Summary of Significant Components of Company's Net Deferred Tax Asset

Significant components of the Company’s net deferred tax assets at December 31, 2022 and 2021 are as follows:

	December 31,
	2022			2021
	(in thousands)
Net operating losses	$	347,880		$	305,824
Tax credits		118,393			106,176
Capitalized research and development expenses		66,849			—
Stock-based compensation		49,916			49,281
Accrued expenses		8,750			6,684
Depreciation and amortization		1,386			1,401
Right of use asset		(2,433	)		(3,702	)
Lease liability		2,803			4,236
Other		(258	)		704
Total net deferred tax asset before valuation    allowance		593,286			470,604
Valuation allowance		(593,286	)		(470,604	)
	$	—		$	—

Summary of Gross Unrecognized Tax Benefits Excluding Interest and Penalties

The following table reconciles the beginning and ending amounts of gross unrecognized tax benefits, excluding interest and penalties, if any, for the years ended December 31, 2022 and 2021:

	2022		2021
	(in thousands)
Balance as of January 1	$	6,084	$	-
Increases related to current year tax positions		697		396
Increases related to prior year tax positions		65		5,688
Balance as of December 31	$	6,846	$	6,084