Note 2 - Summary of Significant Accounting Policies - Antidilutive Securities (Details) - shares	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Antidilutive securities (in shares)	12,554,528	5,996,813	5,762,809
Warrant [Member]
Antidilutive securities (in shares)	7,303,832	0	612,310
Share-Based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	5,250,696	5,996,813	5,039,194
Restricted Stock Units (RSUs) [Member]
Antidilutive securities (in shares)	0	0	111,305