Note 2 - Summary of Significant Accounting Policies - Securities Potentially Dilute Calculation of Diluted Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Antidilutive securities (in shares)	4,911,841	2,083,192	1,098,428
Warrants to Purchase Common Stock - Liability Classified [Member]
Antidilutive securities (in shares)	7,126	56,735	54,989
Warrants to Purchase Common Stock - Equity Classified [Member]
Antidilutive securities (in shares)	90,608	1,957,166	0
Convertible 2020 Notes [Member]
Antidilutive securities (in shares)	0	0	974,139
Share-based Payment Arrangement, Option [Member]
Antidilutive securities (in shares)	4,746,368	1,552	1,561
Stock Appreciation Rights (SARs) [Member]
Antidilutive securities (in shares)	67,739	67,739	67,739