Note 8 - Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Net operating loss carryforwards	$ 18,141	$ 18,677
Research and development credit carryforwards	3,058	3,576
Share-based compensation	449	645
Accrued expenses and reserves	137	127
Depreciation and amortization	38	17
Deferred revenue	253	275
Right of use liability	357	301
Other	23	14
Gross deferred tax assets	22,456	23,632
Less: valuation allowance	(22,121)	(23,324)
Net deferred tax assets	335	308
Right of use asset	(328)	(301)
Net deferred tax assets	7	7
Deferred tax assets, non-current	7	7
Deferred tax liability, non-current