Note 10 - Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2019

Notes Tables

Schedule of Share-based Compensation, Expense [Table Text Block]

	Years ended December 31,
	2019		2018		2017
Cost of goods sold	$	191	$	143	$	140
Research and development		1,115		953		678
Selling, general and administrative		1,416		1,678		1,889
Share-based compensation expense	$	2,722	$	2,774	$	2,707

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

	Options outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining contractual term (years)		Aggregate intrisinsic value (in thousands)
Balance, December 31, 2018		608,547		$	25.20		7.8
Stock options granted		254,785			5.28
Stock options exercised		—			—
Stock options canceled		(41,868	)		26.86
Balance, December 31, 2019		821,464		$	18.99		7.6	$	-
Exercisable and vested, December 31, 2019		428,793		$	23.62		6.6	$	-

Schedule of Nonvested Restricted Stock Units Activity [Table Text Block]

				Weighted
				average
				grant date
	Number of			fair value
	shares			per share
Balance, December 31, 2018		29,698		$	25.56
RSUs granted		34,713			4.75
RSUs vested		(27,430	)		19.46
RSUs forfeited		-			—
Balance, December 31, 2019		36,981		$	10.56

Non-employee Stock Options [Member]

Notes Tables

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

	Years ended December 31,
	2018				2017
Risk-free interest rate		2.80	-	2.95%	2.25	-	2.40%
Volatility		78	-	85%	81	-	87%
Dividend yield			None			None
Expected term (in years)		7.6	-	8.8	8.6	-	9.8

Share-based Payment Arrangement, Option [Member]

Notes Tables

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

	Years ended December 31,
	2019			2018			2017
Risk-free interest rate	1.40	-	2.14%	2.66	-	2.89%	1.76	-	2.25%
Volatility	74	-	94%	81	-	83%	81	-	89%
Dividend yield		None			None			None
Expected term (in years)	6.25	-	10.0		6.25		5.00	-	6.25