Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Components of Income Tax Expense (Benefit)

The following table summarizes the components of our income tax (benefit) expense (in thousands):

	Year ended December 31,
	2021		2020
Current:
Federal	$	—	$	(13)
State	1		1
	1		(12)
Deferred:
Federal	—		12
State	—		—
	—		12
Income tax expense	$	1	$	—

Schedule of Effective Income Tax Rate Reconciliation

The following is a reconciliation of the expected statutory federal income tax provision to our actual income tax provision (in thousands):

	Year ended December 31,
	2021		2020
Expected income tax benefit at federal statutory tax rate	$	(5,840)	$	(3,309)
State income taxes, net of federal benefit	1		(927)
Tax credits	(1,180)		(1,216)
Change in valuation allowance	6,659		2,606
Return to provision adjustments	80		(14)
Stock compensation	243		1,644
Reserve for uncertain tax positions	176		1,179
Other	(138)		37
Income tax expense	$	1	$	—

Schedule of Deferred Tax Assets and Liabilities

The following table summarizes the significant components of our deferred tax assets and liabilities (in thousands):

	December 31,
	2021		2020
Deferred tax assets:
Net operating loss carryovers	$	87,877	$	82,747
Research and development and other tax credits	35,344		34,337
Intangibles and property and equipment basis difference	607		715
Stock compensation expense	587		283
Lease liability	631		88
Other	564		281
Total deferred tax assets	125,610		118,451
Total deferred tax liabilities	(782)		(282)
Net deferred tax asset	124,828		118,169
Valuation allowance	(124,828)		(118,169)
Net deferred tax asset	$	—	$	—

Summary of Income Tax Contingencies

The following table summarizes the changes in the amount of our unrecognized tax benefits (in thousands):

	Year Ended December 31,
	2021		2020
Beginning balance of unrecognized tax benefits	$	17,939	$	16,573
Decrease for prior year tax positions	(1,174)		(1)
Increase for current year tax positions	188		1,367
Total	$	16,953	$	17,939