Note 10 - Income Taxes (Details Textual) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Income Tax Expense (Benefit), Total	$ 20	$ 28	$ 103	$ 62
Operating Loss Carryforwards, Total					$ 258,834
Operating Loss Carryforwards, Subject to Expiration					$ 227,781
Operating Loss Carry Forwards Annual Limit	14,284		14,284
Unrecognized Tax Benefits, Ending Balance	0		0
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued, Total	$ 0		$ 0
Rights [Member]
Term of Extended Rights Plan (Year)			3 years
Threshold Percentage of Beneficial Ownership for Significant Dilution in Ownership Interest			4.90%
Class of Warrant or Right Number of Rights Per Common Stock Share			1
Class of Warrant or Right, Number of Securities Called by Each Warrant or Right (in shares)	0.001		0.001
Class of Warrant or Right, Exercise Price of Warrants or Rights (in dollars per share)	$ 4.25		$ 4.25
Class of Warrant or Right Current Beneficial Ownership Percentage That Will Not Trigger Preferred Share Purchase Rights			4.90%