Note 10 - Equity Incentive Plans (Tables)

6 Months Ended

Jun. 30, 2022

Notes Tables

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

							Weighted					Weighted
	Shares			Number of			Average		Number of			Average
	Available			Options			Exercise		RSUs			Grant Date
	For Grant			Outstanding			Price		Outstanding			Fair Value
Balance at January 1, 2022		5,582,742			10,216,106		$	4.96		—		$	—
Granted		(5,137,646	)		4,628,585		$	4.49		509,061		$	3.95
Exercised		—			(70,643	)	$	1.11		—		$	—
Forfeited		430,720			(429,196	)	$	6.72		(1,589	)	$	2.89
Canceled		28,750			(38,934	)	$	10.44		—		$	—
Balance at June 30, 2022		904,566			14,305,918		$	4.76		507,472		$	3.95

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

	Six Months Ended June 30,
	2022		2021
Risk-free interest rate		1.62% - 3.03%		0.98% - 1.07%
Expected term (in years)		6.02 - 6.08		5.44 - 6.07
Expected volatility		125% - 126%		122% - 131%
Dividend yield		—%		—%

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

	Three Months Ended June 30,				Six Months Ended June 30,
	2022		2021		2022		2021
Research and development	$	2,383	$	644	$	4,410	$	1,223
General and administrative		1,038		1,960		2,141		2,632
Total stock-based compensation	$	3,421	$	2,604	$	6,551	$	3,855