Note 10 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Number of potential common shares excluded (in shares)	32,565,822	8,405,977	33,629,683	7,078,654
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	10,043,575	7,158,387	8,682,997	5,825,082
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	166,142	177,562	172,909	183,544
Warrant [Member]
Number of potential common shares excluded (in shares)	22,356,105	1,070,028	24,773,777	1,070,028