Note 3 - Fair Value Measurements - Fair Value of Warrant Liability (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Warrant Liability [Member]
Balance	$ 178	$ 1,489
Fair value of warrant liability reclassified to equity-Adoption of ASU 2017-11	(56)
Increase (decrease) in fair value of liability during the year ended December 31, 2019		1,311
Balance		178
Decrease in fair value during the year ended December 31, 2018		$ (1,311)
Warrant Liability [Member] \| July 2011 and October 2015 Warrants [Member]
Fair value of warrant liability reclassified to equity-Adoption of ASU 2017-11	(553)
Increase (decrease) in fair value of liability during the year ended December 31, 2019	465
Decrease in fair value during the year ended December 31, 2018	(465)
Warrant Liability [Member] \| Domestic, Foreign, and Ladenburg Warrants [Member]
Issuance of liability	5,269
Increase (decrease) in fair value of liability during the year ended December 31, 2019	(1,214)
Decrease in fair value during the year ended December 31, 2018	1,214
Embedded Derivative Liability [Member]
Issuance of liability	427
Increase (decrease) in fair value of liability during the year ended December 31, 2019	(424)
Decrease in fair value during the year ended December 31, 2018	424
Warrant Liability and Embedded Derivative Liability [Member]
Balance	$ 4,092

Amount of gain (loss) recognized in income from liability measured at fair value on recurring basis using unobservable input (level 3).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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Period Type:	duration

- Definition

Amount of issuances of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

+ References

No definition available.

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- Definition

Fair value of financial instrument classified as a liability measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=117815213&loc=d3e19207-110258

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- Details

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