Note 9 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Effective Income Tax Rate Reconciliation, Change in Deferred Tax Assets Valuation Allowance, Amount	$ 38,551,000	$ 23,824,000	$ 26,040,000
Open Tax Year	2017 2018 2019
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 0	$ 0	$ 0
Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	74,561
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	677,109,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	494,608,000
Foreign Tax Authority [Member]
Operating Loss Carryforwards, Total	$ 6,427,000