Note 12 - Stockholders' Equity - Anti-dilutive Securities (Details) - shares		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020
Anti-dilutive securities (in shares)		8,940,655	9,307,017
Convertible Debt Securities [Member]
Anti-dilutive securities (in shares)		7,960,811	7,300,897
Vested Series A Warrants [Member]
Anti-dilutive securities (in shares)			40,441
Unvested Series A Warrants [Member]
Anti-dilutive securities (in shares)	[1]		69,853
Warrant, Other [Member]
Anti-dilutive securities (in shares)		653,248	1,006,190
Share-based Payment Arrangement, Option [Member]
Anti-dilutive securities (in shares)		326,596	889,636

[1] The unvested Series A warrants were subject to vesting based upon the amount of funds actually received by the Company in the second close of the August 2015 financing which never occurred. The warrants will remain outstanding but unvested until they expire in February 2021.