Note 15 - Warrant Liabilities - Warrant Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021	Dec. 31, 2021	Feb. 18, 2021		Dec. 31, 2020
Proceeds allocated to warrant liabilities	$ 1,244	$ 10,919	$ 2,039	$ 11,921		$ 1,505
Change in fair value of warrants	(795)	(2,507)
Investor Warrants Issued in Connection with 2021 Financing [Member]
Proceeds allocated to warrant liabilities	626	5,942	964	10,476	[1]
Change in fair value of warrants	(338)	(4,534)
Placement Agent Warrants Issued in Connection with 2021 Financing [Member]
Proceeds allocated to warrant liabilities	84	817	132	$ 1,445	[1]
Change in fair value of warrants	(48)	(628)
Investor Warrants Issued in Connection with 2020 Financing [Member]
Proceeds allocated to warrant liabilities	449	3,370	795			1,279
Change in fair value of warrants	(346)	2,091
Placement Agent Warrants Issued in Connection with 2020 Financing [Member]
Proceeds allocated to warrant liabilities	85	590	$ 148			224
Change in fair value of warrants	$ (63)	366
Placement Agent Warrants Issued in Connection with 2018 Financing [Member]
Proceeds allocated to warrant liabilities		200				$ 2	[2]
Change in fair value of warrants		$ 198

[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.