Note 9 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Number of potential common shares excluded (in shares)	8,405,977	5,609,954	7,078,654	4,681,513
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	7,158,387	4,348,383	5,825,082	2,572,413
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	177,562	191,543	183,544	281,015
Warrant [Member]
Number of potential common shares excluded (in shares)	1,070,028	1,070,028	1,070,028	1,828,085