Note 11 - Net Loss Per Share Attributable to Common Stockholders - Common Stock Equivalents Excluded from Calculation of Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities (in shares)	2,166,254	2,200,369	9,720,683
Common Stock Warrants [Member]
Antidilutive Securities (in shares)			659,806	[1]
Employee Stock Option [Member]
Antidilutive Securities (in shares)	2,166,254	2,200,369	1,235,526
Convertible Debt Securities [Member]
Antidilutive Securities (in shares)			243,876	[1]
Convertible Preferred Stock [Member]
Antidilutive Securities (in shares)			7,581,475	[1]

[1] These instruments were either exercised or converted to Common Stock during 2014.