Note 9 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Number of potential common shares excluded (in shares)	7,246,371	3,811,771	6,407,699	4,209,598
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	5,993,823	2,546,295	5,151,103	1,669,709
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	182,520	195,448	186,568	326,493
Warrant [Member]
Number of potential common shares excluded (in shares)	1,070,028	1,070,028	1,070,028	2,213,396