Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

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

	Year Ended December 31,
	2021				2020				2019
Taxes at the U.S. statutory income tax rate		21.0		%		21.0		%		21.0		%
State tax, net of federal benefit		0.9				—				(2.2	)
Other		(0.4	)			1.8				(0.9	)
Stock-based compensation		(1.6	)			(1.6	)			(0.5	)
Research and development tax credits		3.2				2.2				(0.2	)
Rate change		7.3				0.1				(3.9	)
ASC 740-10		(4.2	)			—				—
Change in valuation allowance		(26.2	)			(23.5	)			(13.3	)
Total provision for income taxes		—		%		—		%		—		%

Schedule of Components of Deferred Income Taxes

The tax effects of significant items comprising the Company’s deferred income taxes are as follows:

	December 31,
	2021			2020
	(in thousands)
Deferred tax assets:
Federal and state operating loss carryforwards	$	68,216		$	57,126
Research and development tax credits		7,356			5,411
Stock-based compensation		5,232			4,326
Accruals and other		837			1,145
Intangibles		3,581			1,181
Charitable contributions		266			254
Operating lease liabilities		7,608			8,203
Total deferred tax assets		93,096			77,646
Deferred tax liabilities:
Operating lease right-of-use assets		(4,698	)		(4,946	)
Fixed assets		(1,500	)		(1,750	)
Unrealized gain on equity investment		—			—
Total deferred tax liabilities		(6,198	)		(6,696	)
Valuation allowance		(86,898	)		(70,950	)
Net deferred tax assets	$	—		$	—

Summary of Net Operating Losses and Tax Credit Carryforwards

Net operating losses and tax credit carryforwards as of December 31, 2021 are as follows:

	Amount (in thousands)		Expiration Years
Net operating losses, federal (post December 31, 2017)	$	260,405	Do Not Expire
Net operating losses, federal (pre January 1, 2018)		64,136	2029-2037
Net operating losses, state		93,166	2029-2036
Research and development tax credits, federal		7,173	2034-2041
Research and development tax credits, California		6,040	Indefinite

Schedule of Reconciliation of Unrecognized Tax Benefits

The following table summarizes the activity related to the Company’s unrecognized tax benefits:

	December 31,
	2021		2020			2019
	(in thousands)
Gross unrecognized tax benefits at January 1	$	7,142	$	9,762		$	3,714
Additions for tax positions taken in the current year		3,457		255			6,221
Reductions for tax positions taken in the prior year		2,622		(2,875	)		(173	)
Gross unrecognized tax benefits at December 31	$	13,221	$	7,142		$	9,762