Note 10 - Equity Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2023

Notes Tables

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

							Weighted					Weighted
	Shares			Number of			Option Average		Unvested			RSU Average
	Available			Options			Exercise		RSU Shares			Grant Date
	For Grant			Outstanding			Price		Outstanding			Fair Value
Balance at January 1, 2023		12,074,692			14,725,261		$	4.48		808,310		$	3.57
Granted		(10,577,320	)		7,363,849		$	0.78		3,213,471		$	0.78
Exercised		—			(54,720	)	$	0.31		—		$	—
Released		—			—		$	—		(98,808	)	$	4.13
Forfeited		2,147,228			(1,920,106	)	$	5.24		(227,122	)	$	2.90
Canceled		1,690,941			(1,873,245	)	$	4.43		—		$	—
Balance at June 30, 2023		5,335,541			18,241,039		$	2.92		3,695,851		$	1.17

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

	Six Months Ended June 30,
	2023			2022
Risk-free interest rate		3.45% - 3.86%			1.62% - 3.03%
Expected term (in years)		6.00			6.02 - 6.08
Expected volatility		128%-130%			125% - 126%
Dividend yield		—	%		—	%

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
Research and development	$	2,366	$	2,383	$	3,738	$	4,410
General and administrative		1,561		1,038		2,836		2,141
Total stock-based compensation	$	3,927	$	3,421	$	6,574	$	6,551

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

	Six-Month Offering Period Ending November 30, 2023			Six-Month Offering Period Ending May 31, 2023
Risk-free interest rate		5.37%			4.60%
Expected term (in years)		0.5			0.5
Expected volatility		98.55%			84.66%
Dividend yield		—	%		—	%