Note 15 - Warrant Liabilities - Fair Value of Warrants (Details) $ in Thousands		Jun. 30, 2022 USD ($) yr	Mar. 31, 2022 USD ($) yr	Dec. 31, 2021 USD ($) yr	Jun. 30, 2021 USD ($) yr		Mar. 31, 2021 USD ($) yr		Feb. 18, 2021 USD ($)		Dec. 31, 2020 USD ($) yr
Proceeds allocated to warrant liabilities		$ 257	$ 1,244		$ 6,597		$ 10,919		$ 11,921		$ 1,505
Investor Warrants Issued in Connection with 2021 Financing [Member]
Proceeds allocated to warrant liabilities		167	626	$ 964	3,257		5,942	[1]	10,476
Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Proceeds allocated to warrant liabilities		22	84	132	431	[1]	817	[1]	$ 1,445	[1]
Investor Warrants Issued in Connection with 2020 Financing [Member]
Proceeds allocated to warrant liabilities		57	449	795	2,420		3,370				1,279
Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Proceeds allocated to warrant liabilities		$ 11	$ 85	$ 148	423		590				224
Investor Warrants Issued in Connection with 2018 Financing [Member]
Proceeds allocated to warrant liabilities	[2]				66
Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Proceeds allocated to warrant liabilities					$ 66		$ 200	[2]			$ 2	[2]
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.34	0.73	1.00	2.00		2.64	[1]	4.48
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.34	0.73	1.00	2.00	[1]	2.64	[1]	4.48	[1]
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.34	0.73	1.00	2.00		2.64				1.35
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.34	0.73	1.00	2.00		2.64				1.35
Measurement Input, Share Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				2.00
Measurement Input, Share Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						2.64				1.35
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		2.13	2.38	2.63	3.14		3.38	[1]	3.50
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		2.13	2.38	2.63	3.14	[1]	3.38	[1]	3.50	[1]
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		1.45	1.70	1.95	2.45		2.70				2.95
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		1.45	1.70	1.95	2.45		2.70				2.95
Measurement Input, Expected Term [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				0.05
Measurement Input, Expected Term [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						0.30				0.05
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.0297	0.0235	0.0087	0.0048		0.0041	[1]	0.0026
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.0297	0.0235	0.0087	0.0048	[1]	0.0041	[1]	0.0026	[1]
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.0279	0.0223	0.0072	0.0034		0.0029				0.0017
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.0279	0.0223	0.0072	0.0034		0.0029				0.0017
Measurement Input, Risk Free Interest Rate [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				0.0004
Measurement Input, Risk Free Interest Rate [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						0.0003				0.0008
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		1.24	1.21	1.15	1.14		1.68	[1]	1.68
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		1.24	1.21	1.15	1.14	[1]	1.68	[1]	1.68	[1]
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		1.07	1.27	1.28	1.20		1.20				1.02
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		1.07	1.27	1.28	1.20		1.20				1.02
Measurement Input, Price Volatility [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				0.74
Measurement Input, Price Volatility [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						2.06				0.59
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		3.59	3.59	3.59	3.59		3.59	[1]	3.59
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		4.4875	4.4875	4.4875	4.4875	[1]	4.4875	[1]	4.4875	[1]
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		2.03	2.03	2.03	2.03		2.03				2.03
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		2.03	2.03	2.03	2.03		2.03				2.03
Measurement Input, Exercise Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				1.4927
Measurement Input, Exercise Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						1.4927				1.4927
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.064	0.24	0.37	1.25		2.28	[1]	4.02
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Fair value of the warrants		0.061	0.23	0.36	1.18	[1]	2.24	[1]	3.96	[1]
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.033	0.26	0.46	1.40		1.95				0.74
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Fair value of the warrants		0.036	0.28	0.49	1.40		1.95				0.74
Measurement Input, Quoted Price [Member] | Investor Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]				0.51
Measurement Input, Quoted Price [Member] | Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Fair value of the warrants	[2]						1.55				0.02

[1] Closing date of the 2021 Financing.

[2] The investor warrants issued in the 2018 Financing expired in July 2020. The placement agent warrants issued in the 2018 Financing were cashless exercised in July 2021.