Note 11 - Equity Incentive Plans (Tables)

9 Months Ended

Sep. 30, 2019

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, 2019		200,650			865,163		$	8.13
Authorized under 2019 Plan		1,600,000			—		$	—
Removed from 2016 Plan		(223,389	)		—		$	—
Granted		(1,413,590	)		1,413,590		$	0.76
Forfeited		165,018			(212,731	)	$	1.77
Canceled		22,739			(204,020	)	$	9.15
Balance at September 30, 2019		351,428			1,862,002		$	3.15

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

	Nine Months Ended September 30,
	2019			2018
Risk-free interest rate		1.89% - 2.31%			2.79% - 2.80%
Expected term	5.39 - 6.08 Years			5.84 - 6.05 Years
Expected volatility		83% - 85%			78% - 80%
Dividend yield		—	%		—	%

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2019		2018		2019		2018
	(in thousands)				(in thousands)
Research and development	$	63	$	92	$	222	$	195
General and administrative		83		91		268		192
Total stock-based compensation	$	146	$	183	$	490	$	387