Note 13 - Equity Incentive Plans (Tables)

12 Months Ended

Dec. 31, 2020

Notes Tables

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

							Weighted
	Shares			Number of			Average
	Available			Options			Exercise
	For Grant			Outstanding			Price
Balance at January 1, 2018		—			304,850		$	9.50
Assumed on consummation of Merger		291,102			627,106		$	26.33
Granted		(431,100	)		431,100		$	5.17
Exercised		—			(2,013	)	$	6.49
Forfeited		71,500			(89,903	)	$	5.90
Canceled		269,148			(405,977	)	$	34.64
Balance at December 31, 2018		200,650			865,163		$	8.13
Authorized under 2019 Plan on Adoption		1,600,000			—		$	—
Removed from 2016 Plan		(223,389	)		—		$	—
Granted		(1,791,030	)		1,791,030		$	0.67
Forfeited		483,849			(592,528	)	$	1.57
Canceled		25,100			(252,013	)	$	9.25
Balance at December 31, 2019		295,180			1,811,652		$	2.74
Authorized under 2019 Plan Amendment		6,400,000			—		$	—
Granted		(5,579,800	)		5,579,800		$	2.66
Exercised		—			(414,676	)	$	1.45
Forfeited		105,910			(105,992	)	$	1.65
Canceled		9,573			(57,751	)	$	10.57
Balance at December 31, 2020		1,230,863			6,813,033		$	2.70

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

	Year Ended December 31,
	2020	2019	2018
Risk-free interest rate	0.40% - 0.88%	1.68% - 2.31%	2.79% - 2.80%
Expected term (in years)	5.22 - 10.00	5.39 - 10.00	5.84 - 6.05
Expected volatility	94% - 111%	83% - 85%	78% - 80%
Dividend yield	—%	—%	—%

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

	Year Ended December 31,
	2020		2019		2018
Research and development	$	1,563	$	253	$	254
General and administrative		2,795		374		285
Total stock-based compensation	$	4,358	$	627	$	539