Income Taxes (Tables)

12 Months Ended

Dec. 31, 2019

Income Taxes

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

	December 31,
	2019		2018
Deferred tax assets:
Net operating loss carryforwards	$	55,216	$	51,240
Research credit carryforward		7,609		6,904
Stock options and other		3,225		2,655
Total gross deferred tax assets		66,050		60,799
Valuation allowance for deferred tax assets		(66,050)		(60,799)
Net deferred tax assets	$	—	$	—

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

	December 31,
	2019		2018		2017
Federal income tax at statutory rate	21.0	%	21.0	%	34.0	%
State income tax benefit, net of federal benefit	7.0	%	6.0	%	6.0	%
Research and development tax credits	4.0	%	3.0	%	3.0	%
Effect of tax rate changes	0.0	%	0.0	%	-94.0	%
Other	-4.0	%	-4.0	%	-1.0	%
Decrease (increase) to valuation allowance	-28.0	%	-24.0	%	52.0	%
Effective income tax rate	0.0	%	2.0	%	0.0	%