Note 8 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Number of potential common shares excluded (in shares)	5,609,954	6,839,645	4,681,513	3,784,655
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	4,348,383	783,794	2,572,413	388,377
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	191,543	1,338,916	281,015	751,332
Warrant [Member]
Number of potential common shares excluded (in shares)	1,070,028	4,716,935	1,828,085	2,644,946