Income Taxes (Tables)

12 Months Ended

Dec. 31, 2018

Income Taxes

Schedule of tax effects of temporary differences that give rise to significant portions of deferred tax assets

	December 31,
	2018		2017
Deferred tax assets:
Net operating loss carryforwards	$	51,240	$	47,427
Research credit carryforward		6,904		6,296
Stock options and other		2,655		2,296
Total gross deferred tax assets		60,799		56,019
Valuation allowance for deferred tax assets		(60,799)		(56,019)
Net deferred tax assets	$	—	$	—

Schedule of reconciliation of U.S. statutory income tax rate to effective tax rate

	December 31,
	2018		2017		2016
Federal income tax at statutory rate	21.0	%	34.0	%	34.0	%
State income tax benefit, net of federal benefit	6.0	%	6.0	%	6.0	%
Research and development tax credits	3.0	%	3.0	%	2.0	%
Effect of tax rate changes	0.0	%	-94.0	%	0.0	%
Other	-4.0	%	-1.0	%	1.0	%
Decrease (increase) to valuation allowance	-24.0	%	52.0	%	-33.0	%
Effective income tax rate	2.0	%	0.0	%	10.0	%