Note 8 - Net Loss Per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 2018

Notes Tables

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2018		2017		2018		2017
Outstanding stock options		4,597,226		2,683,912		4,597,226		2,683,912
Outstanding ESPP shares		26,642		34,464		26,642		34,464
Convertible preferred stock		22,112,775		22,112,775		22,112,775		22,112,775
		26,736,643		24,831,151		26,736,643		24,831,151