Note 16 - Warrant Liabilities - Warrant Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Jan. 17, 2018
Proceeds allocated to warrant liabilities	$ 956	$ 801	$ 606	$ 2,275
Change in fair value of warrants	350	(1,474)
Investor Warrants [Member]
Proceeds allocated to warrant liabilities	793	664	503	1,890
Change in fair value of warrants	290	(1,226)
Placement Agent Warrants [Member]
Proceeds allocated to warrant liabilities	163	137	$ 103	$ 385
Change in fair value of warrants	$ 60	$ (248)