Note 13 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ (16,728,000)	$ (9,949,000)
Income (Loss) from Continuing Operations before Income Taxes, Foreign	(83,000)	(150,000)
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	197,000	$ (681,000)
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	126,582,000
Operating Loss Carryforwards, Subject to Expiration	106,226,000
Operating Loss Carryforwards, Not Subject to Expiration	20,356,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	1,601,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	41,511,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	1,583,000
Foreign Tax Authority [Member]
Operating Loss Carryforwards, Total	$ 796,000