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

3 Months Ended

Mar. 31, 2019

Notes Tables

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

	Three Months Ended March 31,
	2019		2018
Outstanding stock options		5,779,726		4,380,937
Outstanding ESPP shares		267,242		55,716
Convertible preferred stock		21,771,032		22,112,775
		27,818,000		26,549,428