Note 8 - Net Loss Per Share - Schedule of Antidilutive Securities (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Number of potential common shares excluded (in shares)	6,839,645	357,347	3,784,655	402,385
Employee Stock Option [Member]
Number of potential common shares excluded (in shares)	783,794	176,502	388,377	100,505
Series A Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)		42,480		74,651
Series B Convertible Preferred Stock [Member]
Number of potential common shares excluded (in shares)	1,338,916		751,332
Warrant [Member]
Number of potential common shares excluded (in shares)	4,716,935	138,365	2,644,946	227,229