Note 9 - Net Loss Per Share Attributable to Common Stockholders (Tables)

9 Months Ended

Sep. 30, 2017

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,
	2017		2016		2017		2016
Outstanding stock options		2,683,912		2,169,617		2,683,912		2,169,617
Outstanding ESPP shares		34,464		10,913		34,464		10,913
		2,718,376		2,180,530		2,718,376		2,180,530