Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Components of Income Tax (Benefit) Expense

The Company’s loss before tax is only attributable to U.S. operations. The components of the income tax (benefit) expense are as follows (in thousands):

	Year Ended December 31,
	2021		2020		2019
Current (benefit from) provision for income taxes:
Federal	$	—	$	—	$	—
State		—		—		—
Total current (benefit from) provision for income    taxes		—		—		—
Deferred (benefit from) provision for income taxes:		—		—		—
Federal		—		—		—
State		—		—		—
Total deferred tax (benefit from) provision for    income taxes		—		—		—
(Benefit from) provision for income taxes	$	—	$	—	$	—

Reconciliation of the Federal Statutory Income Tax Rate to the Company's Effective Income Tax Rate

A reconciliation of the federal statutory income tax rate to the Company’s effective income tax rate is as follows:

	Year Ended December 31,
	2021			2020			2019
Federal statutory income tax rate		(21.0	%)		(21.0	%)		(21.0	%)
State, net of federal benefit		(0.4	)		—			—
Permanent items		1.2			2.1			1.3
Excess tax benefit for stock-based compensation		(3.0	)		(40.9	)		(13.3	)
Tax credits		(3.1	)		(13.4	)		(38.3	)
Change in valuation allowance		22.9			70.4			70.3
Non-deductible executive compensation		3.3			2.7			1.0
Other		0.1			0.1			—
(Benefit from) provision for income taxes		—	%		—	%		—	%

Tax Effects of Temporary Differences and Carryforwards that Give Rise to Significant Portions of the Deferred Tax Assets

The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets consist of the following (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	143,914		$	120,347
Tax credits		54,585			49,229
Stock-based compensation		5,485			4,165
Reserves and accruals		3,034			1,770
Deferred revenue		7,657			7,684
Lease liability		10,628			8,299
Gross deferred tax assets		225,303			191,494
Less: valuation allowance		(216,025	)		(183,948	)
Total deferred tax assets		9,278			7,546
Deferred tax liabilities:
Property, plant and equipment		(3,967	)		(1,894	)
Right of use asset		(5,311	)		(5,652	)
Total deferred tax liabilities		(9,278	)		(7,546	)
Net deferred tax assets	$	—		$	—

Reconciliation of the Company's Unrecognized Tax Benefits

A reconciliation of the Company’s unrecognized tax benefits for the years ended December 31, 2021, 2020 and 2019, is as follows (in thousands):

	Unrecognized Income Tax Benefits
Balance as of December 31, 2019	$	29,176
Additions for current tax positions		1,317
Releases		(29	)
Balance as of December 31, 2020		30,464
Additions for current tax positions		1,269
Additions for prior tax positions		1,432
Releases		(58	)
Balance as of December 31, 2021	$	33,107