Note 2 - Summary of Significant Accounting Policies - Adoption of New Accounting Pronouncement (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2019
Additional paid-in capital	$ 286,832	$ 286,276
Accumulated deficit	(266,284)	(258,854)
Change in value of warrants, gain (loss)
Net loss	(7,429)	(8,701)
Net loss	$ (7,430)	(8,700)
Warrant [Member]
Warrant liability
Warrant [Member] | Accounting Standards Update 2017-11 [Member]
Warrant liability			$ (2,192)
Change in value of warrants, gain (loss)		(1,267)
Previously Reported [Member]
Additional paid-in capital		279,306
Accumulated deficit		(252,809)
Change in value of warrants, gain (loss)		1,267
Net loss		(7,434)
Previously Reported [Member] | Warrant [Member]
Warrant liability		925
Restatement Adjustment [Member] | Accounting Standards Update 2017-11 [Member]
Additional paid-in capital		6,970
Accumulated deficit		(4,778)
Change in value of warrants, gain (loss)		(1,267)
Net loss		(1,267)
Restatement Adjustment [Member] | Accounting Standards Update 2017-11 [Member] | Retained Earnings [Member]
Change in value of warrants, gain (loss)		(1,267)
Restatement Adjustment [Member] | Warrant [Member] | Accounting Standards Update 2017-11 [Member]
Warrant liability		(2,192)
Change in value of warrants, gain (loss)		$ 1,267