Note 12 - Net Loss Per Share Attributable to Common Stockholders (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block]

	Year Ended December 31,
	2017		2016		2015
Outstanding stock options		2,681,072		2,166,254		2,200,369
Convertible preferred stock		22,112,775		-		-
		24,793,847		2,166,254		2,200,369