Income Taxes (Tables)

12 Months Ended

Dec. 31, 2023

Income Tax Disclosure [Abstract]

Summary of Income (Loss) Before Income Tax Expense

Loss before income tax expense consists of the following:

	Year Ended December 31,
	2023			2022			2021
	(in thousands)
Domestic	$	(541,656	)	$	(532,539	)	$	(457,693	)
Foreign		167			(245	)		(199	)
	$	(541,489	)	$	(532,784	)	$	(457,892	)

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,
	2023			2022			2021
Tax due at statutory rate		21.0	%		21.0	%		21.0	%
State taxes, net of federal		4.1			1.8			1.9
Stock-based compensation		(1.7	)		(1.9	)		(5.2	)
Federal and state tax credits		2.4			2.1			3.5
Change in valuation allowance		(26.2	)		(23.0	)		(20.7	)
Other		0.4			—			(0.5	)
		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, 2023 and 2022 are as follows:

	December 31,
	2023			2022
	(in thousands)
Net operating losses	$	428,785		$	347,880
Tax credits		133,602			118,393
Capitalized research and development expenses		110,690			66,849
Stock-based compensation		53,860			49,916
Accrued expenses		7,018			8,750
Depreciation and amortization		1,456			1,386
Lease liability		1,207			2,803
Right of use asset		(1,042	)		(2,433	)
Other		(382	)		(258	)
Total net deferred tax asset before valuation    allowance		735,194			593,286
Valuation allowance		(735,194	)		(593,286	)
	$	—		$	—

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, 2023, 2022 and 2021:

	2023		2022		2021
	(in thousands)
Balance as of January 1	$	6,846	$	6,084	$	—
Increases related to current year tax positions		655		697		396
Increases related to prior year tax positions		242		65		5,688
Balance as of December 31	$	7,743	$	6,846	$	6,084