Note 14 - Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]

	Year ended December 31,
	2020			2019
Expected dividend yield		0%			0%
Expected volatility	82%	-	126%	81%	-	92%
Risk-free interest rate	0.2%	-	1.69%	1.39%	-	2.66%
Expected life (in years)	3.8	-	6.1	5.5	-	6.1

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

	Number of Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)
Options outstanding at December 31, 2019		1,830,958		$	30.71		7.36
Granted		3,005,964			0.54
Forfeited		(293,102	)		19.08
Cancelled		(181,948	)		35.57
Exercised		-			-
Options Outstanding December 31, 2020		4,361,872		$	10.49		6.05

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

	Number of Shares		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (Years)
Exercisable at December 31, 2020		1,282,678	$	27.71		4.81
Vested or expected to vest at December 31, 2020		4,141,694	$	10.89		6.05