Note 11 - Stock-based Compensation (Tables)

3 Months Ended

Mar. 31, 2024

Notes Tables

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

	Number of Shares			Weighted-Average Exercise Price		Weighted-Average Remaining Contractual Term (Years)		Aggregate Intrinsic Value (Millions)
Outstanding at December 31, 2023		10,444,679		$	3.20		4.80
Granted		5,552,790			0.26
Cancelled		(36,406	)		10.24
Outstanding at March 31, 2024		15,961,063		$	2.16		5.37	$	-
Vested or expected to vest at March 31, 2024		14,795,731		$	2.30		5.27	$	-
Exercisable at March 31, 2024		7,862,867		$	3.97		4.25	$	-

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

	Three Months Ended March 31,
	2024				2023
Expected volatility		126%	-	127%		124%	-	126%
Risk-free interest rate		4.06%	-	4.07%		3.73%	-	4.14%
Expected life (in years)		4.3	-	4.5		4.3	-	4.5
Expected dividend yield		0%				0%
Weighted average grant date fair value		$0.22				$0.60

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

	Number of Shares			Weighted-Average Grant Date Fair Value
Unvested at December 31, 2023		12,326,177		$	0.81
Granted		14,647,450		$	0.26
Vested		(4,655,843	)	$	0.97
Forfeited		(1,358,970	)	$	0.67
Unvested at March 31, 2024		20,958,814		$	0.40

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

	Three Months Ended March 31,
	2024		2023
	(in thousands)
Stock options	$	425	$	665
Restricted stock units		956		859
Performance restricted stock units		364		392
	$	1,745	$	1,916