Note 11 - Stock-based Compensation (Tables)

6 Months Ended

Jun. 30, 2022

Notes Tables

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

	Number of Shares			Weighted- Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)
Balance at December 31, 2021		4,640,660		$	6.64		5.66
Granted		2,555,396			0.77
Forfeited		(23,047	)		3.22
Cancelled		(16,983	)		33.27
Exercised		(43,453	)		0.41
Balance at June 30, 2022		7,112,573		$	4.52		5.71

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)		Aggregate Intrinsic Value (Millions)
Exercisable at June 30, 2022		3,119,355	$	8.02		5.08	$	-
Vested or expected to vest at June 30, 2022		6,777,170	$	4.67		5.67	$	-

Share-Based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block]

	Number of Restricted Stock Units Outstanding			Weighted- Average Grant Date Fair Value
Unvested December 31, 2021		3,839,030		$	2.36
Granted		6,040,915			0.75
Vested		(1,794,623	)		2.47
Forfeited		(100,047	)		1.36
Unvested Jun 30, 2022		7,985,275		$	1.13

Share-Based Payment Arrangement, Cost by Plan [Table Text Block]

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
	(in thousands)				(in thousands)
Stock options	$	924	$	1,087	$	1,901	$	2,207
Restricted stock units		822		690		1,707		1,293
Performance restricted stock units		337		33		720		70
	$	2,083	$	1,810	$	4,328	$	3,570

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

	Six Months Ended June 30,
	2022				2021
Expected dividend yield			0%			0%
Expected volatility		128%	-	133%	118%	-	136%
Risk-free interest rate		1.25%	-	2.98%	0.33%	-	0.58%
Expected life (in years)		4.3	-	4.5	3.8	-	4.5