Note 11 - Warrant Liability - Outstanding Warrant Liability (Details) - USD ($)	Sep. 30, 2019	Aug. 13, 2019	Aug. 08, 2019	Jan. 01, 2019	Dec. 31, 2018
Shares (in shares)	8,588,000			334,109	544,000
Warrant liability	$ 3,902,000				$ 178,000
The 2011 Warrants [Member]
Shares (in shares)	35,000
Warrant liability	$ 18,000
October 2015 Warrants [Member]
Shares (in shares)	38,000
Warrant liability	$ 20,000
The 2019 Domestic Warrants [Member]
Shares (in shares)	4,199,000
Warrant liability	$ 2,296,000	$ 3,100,000	$ 3,100,000
The 2019 Foreign Warrants [Member]
Shares (in shares)	2,700,000
Warrant liability	$ 1,477,000	2,000,000	$ 2,000,000
The 2019 Ladenburg Warrants [Member]
Shares (in shares)	168,000
Warrant liability	$ 91,000	$ 124,000
July 2011, Long-term, Short-term, and October 2015 Warrants [Member]
Shares (in shares)	7,140,000
Warrant liability	$ 3,902,000