Note 3 - Fair Value Measurements (Details Textual) - USD ($) $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended	12 Months Ended
	Aug. 31, 2019	Jul. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Sep. 30, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019	Jan. 01, 2019	Dec. 31, 2016
Class of Warrant or Right, Outstanding						8,588,000	544,000	544,000			565,000
Class of Warrant or Right, Exercised During Period						394,000		21,000
Fair Value Adjustment of Warrants						$ (749)	$ (1,311)	$ 101
Reclassification of Warrant Liability to Equity						$ 56
Class of Warrant or Right, Issued During Period						8,438,000
July 2011 and October 2015 Warrants [Member]
Warrants and Rights Outstanding			$ 200	$ 400	$ 200
Class of Warrant or Right, Outstanding						73,107				334,109
Class of Warrant or Right, Exercised During Period		102,602	102,602	158,400
Class of Warrant or Right, Number of Securities Called by Warrants or Rights		102,602	102,602	158,400	102,602
Warrants Reclassified Upon Adoption of ASU 2017-11 [Member]
Warrants and Rights Outstanding, Change in Fair Value						$ (88)
Fair Value Adjustment of Warrants						(465)
Reclassification of Warrant Liability to Equity					$ 553
The August 2019 Warrants [Member]
Warrants and Rights Outstanding	$ 5,300
Fair Value Adjustment of Warrants						(1,200)
Class of Warrant or Right, Issued During Period	7,066,508
Class of Warrant or Right, Number of Securities Called by Warrants or Rights	7,066,508
Accounting Standards Update 2017-11 [Member]
Warrants and Rights, Reclassified to Equity										210,586
Warrants and Rights Outstanding						$ (56)			$ (56)	$ (56)