Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

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,
	2019			2018
Current:
Federal	$	(13	)	$	(26	)
State	1			1
	(12		)	(25		)
Deferred:
Federal	13			87
State	—			—
	13			87
Income tax expense	$	1		$	62

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,
	2019			2018
Expected income tax benefit at federal statutory tax rate	$	(3,904	)	$	(10,216	)
State income taxes, net of federal benefit	(1,390		)	(3,005		)
Tax credits	(374		)	(3,666		)
Change in valuation allowance	603			12,706
Return to provision adjustments	(358		)	441
Stock compensation	3,934			251
Reserve for uncertain tax positions	1,444			3,596
Other	46			(45		)
Income tax expense	$	1		$	62

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,
	2019			2018
Deferred tax assets:
Net operating loss carryovers	$	79,675		$	74,965
Research and development and other tax credits	33,429			33,121
Deferred revenue	1			16
Intangibles and property and equipment basis difference	782			—
Stock compensation expense	1,389			5,033
Lease liability	164			—
Other	461			2,027
Total deferred tax assets	115,901			115,162
Total deferred tax liabilities	(325		)	(176		)
Net deferred tax asset	115,576			114,986
Valuation allowance	(115,564		)	(114,960		)
Net deferred tax asset	$	12		$	26

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,
	2019			2018
Beginning balance of unrecognized tax benefits	$	14,700		$	4,421
(Decrease) increase for prior year tax positions	(7		)	5,961
Increase for current year tax positions	1,880			4,318
Total	$	16,573		$	14,700