Note 3 - Fair Value Measurements - Fair Value of Warrant Liability (Details) $ in Thousands	3 Months Ended
Mar. 31, 2020 USD ($)
Balance	$ 4,092
Balance	3,953
Warrant Liability [Member]
Decrease in fair value of warrant liability	(122)
Embedded Derivative Liability [Member]
Decrease in fair value of warrant liability	(2)
Expiration of Warrants [Member]
Decrease in fair value of warrant liability	$ (15)

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.

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

Name:	us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant