Note 10 - Income Taxes - Summary of Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Net operating loss carryforwards	$ 11,090	$ 6,742
Federal and state tax credits	3,587	3,122
Accrued expenses		411
Patents	74	132
Stock-based compensation		1,782
Other	59	169
Total deferred tax assets	14,810	12,358
Valuation allowance	(14,810)	(12,358)
Net deferred assets