Note 6 - Stockholders' Equity and Stock-based Compensation (Tables)

12 Months Ended

Dec. 31, 2023

Notes Tables

Schedule of Stockholders' Equity Note, Warrants or Rights [Table Text Block]

						Weighted
						Average
				Weighted		Remaining
	Number of			Average		Contractual
	Shares			Exercise Price		Life (in Years)
Warrants outstanding at December 31, 2022		7,303,832		$	2.05		4.43
Issued		—			—
Exercised		(7,237,657	)		2.05
Expired/Redeemed		(66,175	)		2.05
Warrants outstanding at December 31, 2023		—		$	—		—

Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block]

	Year Ended December 31,
	2023		2022
Cost of revenues	$	—	$	217
Research and development		3,491		1,563
Sales and marketing		—		733
General and administrative		3,690		2,678
Total stock-based compensation expense	$	7,181	$	5,191

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

	Year Ended December 31,
	2023		2022
Time-based options	$	3,827	$	4,467
Performance-based options		1,977		233
Market-based options		1,130		—
ESPP		247		491
Total stock-based compensation expense	$	7,181	$	5,191

Share-Based Payment Arrangement, Option [Member]

Notes Tables

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

	Year Ended December 31,
	2023		2022
Expected term in years		5.0 - 8.0		5.3 - 6.8
Expected volatility		89 - 95%		83 - 88%
Risk-free interest rate		3.7 - 4.4%		1.9 - 3.2%
Dividend yield		—		—

	Year Ended December 31,
	2023		2022
Expected term in years		4.0 - 6.3		—
Expected volatility		90%		—
Risk-free interest rate		3.4% - 3.8%		—
Dividend yield		—		—

Market-based Options [Member]

Notes Tables

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

	Stock Options Outstanding
	Number of shares		Weighted average exercise price		Weighted average remaining life (in years)
Balances — December 31, 2022		—	$	—		—
Options granted		2,100,000		6.78
Options exercised		—		—
Options canceled		—		—
Options expired		—		—
Balances — December 31, 2023		2,100,000	$	6.78		9.44
Exercisable — December 31, 2023		—		—		—

Performance Options [Member]

Notes Tables

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

	Stock Options Outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining life (in years)
Balances — December 31, 2022		520,302		$	10.08		7.02
Options granted		848,000			3.13
Options exercised		—			—
Options canceled		(53,500	)		2.31
Options expired		(90,672	)		11.35
Balances — December 31, 2023		1,224,130		$	5.51		8.53
Exercisable — December 31, 2023		443,628		$	7.57		7.75

Time-based Options [Member]

Notes Tables

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

	Stock Options Outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining life (in years)
Balances — December 31, 2022		4,730,394		$	12.95		6.16
Options granted		2,390,386			4.7
Options exercised		(301,254	)		3.89
Options canceled		(262,994	)		6.06
Options expired		(414,626	)		13.01
Balances — December 31, 2023		6,141,906		$	10.48		7.07
Exercisable — December 31, 2023		3,390,035		$	14.47		5.28

The 2017 Employee Stock Purchase Plan [Member]

Notes Tables

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

	Year Ended December 31,
	2023		2022
Expected term in years		0.5 - 1.0		0.5 - 1.0
Expected volatility		83%		83%
Risk-free interest rate		5.1% - 5.5%		0.6% - 3.5%
Dividend yield		—		—

The 2015 Plan, 2017 Plan and Inducement Plan [Member]

Notes Tables

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

	Stock Options Outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining life (in years)
Balances — December 31, 2022		5,250,696		$	12.67		6.24
Options granted		5,338,386			5.26
Options exercised		(301,254	)		3.89
Options canceled		(316,494	)		5.42
Options expired		(505,298	)		12.71
Balances — December 31, 2023		9,466,036		$	9.01		7.78
Exercisable — December 31, 2023		3,833,663		$	13.67		5.56