Note 8 - Stock Based Awards (Tables)

9 Months Ended

Sep. 30, 2021

Notes Tables

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

						Weighted
						Average
				Weighted		Remaining		Aggregate
				Average		Contractual		Intrinsic
	Number of			Exercise		Life		Value
	Shares			Price		(in years)		(in thousands)
Balances, January 1, 2021		2,173,776		$	9.59
Options granted		865,674			5.55
Options cancelled		(457,323	)		34.53
Options exercised		(148,452	)		1.91
Balances, September 30, 2021		2,433,675		$	3.93		7.0	$	3,269
Outstanding and expected to vest as of September 30, 2021		2,278,219		$	3.77		6.9	$	3,269
Exercisable as of September 30, 2021		1,473,616		$	2.44		5.6	$	3,269

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

	September 30,			September 30,
	2021			2020
Expected volatility		114.4	%		112.3	%
Risk-free interest rate		0.7	%		1.0	%
Dividend yield		0.0	%		0.0	%
Expected life (in years)		5.9			6.0