Note 10 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2023

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, 2022		7,584,967		$	4.22		5.31
Granted		2,748,415			0.73
Forfeited		-			-
Cancelled		(913	)		4.21
Exercised		(13,300	)		0.38
Balance at March 31, 2023		10,319,169		$	3.30		5.54

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 March 31, 2023		4,843,264	$	5.96		4.80	$	0.4
Vested or expected to vest at March 31, 2023		9,645,630	$	3.47		5.47	$	0.6

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

	Three Months Ended March 31,
	2023			2022
Expected dividend yield		0%			0%
Expected volatility	124%	-	126%	131%	-	133%
Risk-free interest rate	3.73%	-	4.14%	1.25%	-	1.94%
Expected life (in years)	4.3	-	4.5	4.3	-	4.5

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, 2022		8,483,491		$	1.04
Granted		7,340,630			0.73
Vested		(3,082,354	)		1.18
Forfeited		(84,673	)		1.13
Unvested March 31, 2023		12,657,094		$	0.83

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

	Three Months Ended March 31,
	2023		2022
	(in thousands)
Stock options	$	665	$	978
Restricted stock units		859		883
Performance restricted stock units		392		384
	$	1,916	$	2,245