Note 7 - Stock Option Plans and Stock-based Compensation (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

Share-based Payment Arrangement, Option, Activity [Table Text Block]

	Shares available for Grant		Number of Options Outstanding		Weighted Average Exercise price per share
Balance, January 1, 2020		1,384,761		65,471	$	16.86
Granted		81,227		81,227	$	4.38
Balance, September 30, 2021		1,303,534		146,698	$	9.95
Vested, September 30, 2021		—		65,471	$	16.86
Vested and expected to vest, September 30, 2021		—		146,698	$	9.95

Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested and Expected to Vest, Outstanding and Exercisable [Table Text Block]

Options Outstanding		Weighted average remaining contractual life (years)		Options Exercisable		Weighted Average Exercise Prices
	48,724		1.10		48,724	$	11.89
	16,747		3.19		16,747	$	31.33
	65,227		9.54		—	$	4.30
	16,000		9.71		—	$	4.73
	146,698		6.03		65,471	$	9.95