Note 8 - Stockholders' Equity (Tables)

9 Months Ended

Sep. 30, 2020

Notes Tables

Schedule of Common Stock Capital Shares Reserved for Future Issuance [Table Text Block]

	September 30, 2020		December 31, 2019
Stock options and restricted stock units issued and outstanding		5,279,277		5,562,484
Stock options and restricted stock units available for grant under stock option plans		3,036,308		1,954,804
Common stock available for the Employee Stock Purchase Plan		1,571,395		173,168
Total		9,886,980		7,690,456