Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Reconciliation of Effective Income Tax Rate

The effective tax rate of the provision for income taxes differs from the federal statutory rate as follows:

	Year Ended December 31,
	2021			2020			2019
Federal statutory income tax rate		21.00	%		21.00	%		21.00	%
Change in valuation allowance		(31.07	)		(26.75	)		(27.42	)
Tax credits		12.14			6.43			7.27
State income taxes, net of federal benefit		0.73			0.33			0.25
Stock-based compensation		(3.02	)		(1.00	)		(0.89	)
Other, net		0.03			(0.01	)		(0.21	)
Provision for income taxes		(0.19	)%		—	%		—	%

Components of Deferred Tax Assets and Liabilities

The components of the deferred tax assets and liabilities are as follows (in thousands):

	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	60,273		$	54,523
Tax credits		5,486			1,068
Depreciation and amortization		1,863			2,067
Stock-based compensation		3,004			2,452
Accruals and reserves		646			606
Lease liabilities		156			278
Gross deferred tax assets		71,428			60,994
Valuation allowance		(71,291	)		(60,747	)
Total deferred tax assets		137			247
Deferred tax liabilities:
Right-of-use assets		(137	)		(247	)
Total deferred tax liabilities		(137	)		(247	)
Net deferred tax assets	$	—		$	—

Schedule of Unrecognized Tax Benefits Roll Forward

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

	Year Ended December 31,
	2021		2020			2019
Balance at beginning of year	$	451	$	3,277		$	4,634
Additions based on tax positions related to prior    year		—		—			—
Additions based on tax positions related to    current year		1,499		81			2,443
Reductions based on tax positions related to    prior year		—		(2,907	)		(3,800	)
Reductions based on tax positions related to    current year		—		—			—
Balance at end of year	$	1,950	$	451		$	3,277