Note 13 - Income Taxes (Details Textual) - USD ($)	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Income (Loss) from Continuing Operations before Income Taxes, Domestic	$ (9,934,000)	$ (45,458,000)
Income (Loss) from Continuing Operations before Income Taxes, Foreign	(150,000)	(212,000)
Income Tax Expense (Benefit), Total	0	(4,730,000)
Valuation Allowance, Deferred Tax Asset, Increase (Decrease), Amount	(681,000)	$ (2,266,000)
Domestic Tax Authority [Member]
Operating Loss Carryforwards, Total	121,195,000
Operating Loss Carryforwards, Subject to Expiration	109,293,000
Operating Loss Carryforwards, Not Subject to Expiration	11,902,000
Domestic Tax Authority [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	1,591,000
State and Local Jurisdiction [Member]
Operating Loss Carryforwards, Total	43,870,000
State and Local Jurisdiction [Member] | Research Tax Credit Carryforward [Member]
Tax Credit Carryforward, Amount	1,476,000
Foreign Tax Authority [Member]
Operating Loss Carryforwards, Total	$ 2,495,000