Note 8 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Number of potential common shares excluded (in shares)	3,811,771	3,377,129	4,209,598	2,239,136
Share-based Payment Arrangement, Option [Member]
Number of potential common shares excluded (in shares)	2,546,295	200,954	1,669,709	187,391
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	195,448	900,367	326,493	452,671
Warrant [Member]
Number of potential common shares excluded (in shares)	1,070,028	2,275,808	2,213,396	1,599,074