Note 14 - Income Taxes (Details Textual) - USD ($) Pure in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Expense (Benefit), Total	$ 0
Effective Income Tax Rate Reconciliation, Percent, Total	0.00%	0.00%
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	$ 4,593,000	$ (4,352,000)
Deferred Tax Assets, Tax Credit Carryforwards, Research	781,000	631,000
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	0
Unrecognized Tax Benefits, Ending Balance	231,000	$ 245,000	$ 223,000
Unrecognized Tax Benefits that Would Impact Effective Tax Rate	0
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	112,951,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	34,469,000
State and Local Jurisdiction [Member] | California Franchise Tax Board [Member]
Deferred Tax Assets, Tax Credit Carryforwards, Research	768,000
State and Local Jurisdiction [Member] | Colorado Department Of Revenue [Member] | Job Growth Incentive Tax Credits [Member]
Deferred Tax Assets, Tax Credit Carryforwards, Total	$ 451,000