Note 11 - Share-based Compensation (Tables)

9 Months Ended

12 Months Ended

Sep. 30, 2019

Dec. 31, 2018

Notes Tables

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

	Three months ended September 30,				Nine months ended September 30,
	2019		2018		2019		2018
Cost of goods sold	$	38	$	39	$	130	$	105
Research and development		293		250		787		711
Selling, general and administrative		425		441		1,224		1,267
Share-based compensation expense	$	756	$	730	$	2,142	$	2,083

	Years ended December 31,
	2018		2017		2016
Cost of goods sold	$	143	$	140	$	14
Research and development		953		678		127
Selling, general and administrative		1,678		1,889		801
Share-based compensation expense	$	2,774	$	2,707	$	942

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

	Options outstanding
	Number of shares			Weighted average exercise price
Balance, December 31, 2018		608,485		$	25.16
Stock options granted		254,785			5.28
Stock options exercised		—			-
Stock options canceled		(15,122	)		14.16
Balance, September 30, 2019		848,148		$	18.90
Exercisable and vested, September 30, 2019		390,199		$	24.17

	Options outstanding
	Number of shares			Weighted average exercise price		Weighted average remaining contractual term (years)		Aggregate intrisinsic value (in thousands)
Balance, December 31, 2017		4,213,100		$	2.96		8.1	$	1,890
Stock options granted		1,698,452			2.41
Stock options exercised		(2,488	)		1.80
Stock options canceled		(431,700	)		2.92
Balance, December 31, 2018		5,477,364		$	2.80		7.8	$	-
Exercisable and vested, December 31, 2018		2,346,990		$	2.72		6.9	$	-

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

				Weighted
				average
				grant date
	Number of			fair value
	S hares			per share
Balance, December 31, 2018		29,694		$	25.56
RSUs granted		34,713		$	4.75
RSUs vested		(2,272	)	$	99.36
RSUs forfeited		-			-
Balance, September 30, 2019		62,135		$	10.55

				Weighted
				average
				grant date
	Number of			fair value
	shares			per share
Balance, December 31, 2017		97,996		$	8.71
RSUs granted		226,471		$	1.36
RSUs vested		(57,108	)	$	7.03
RSUs forfeited		-			—
Balance, December 31, 2018		267,359		$	2.84

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			2016
Risk-free interest rate	2.80	-	2.95%	2.25	-	2.40%	1.60	-	2.42%
Volatility	78	-	85%	81	-	87%	89	-	91%
Dividend yield	None			None			None
Expected term (in years)	7.6	-	8.8	8.6	-	9.8	9.6	-	9.9

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,
	2018			2017			2016
Risk-free interest rate	2.66	-	2.89%	1.76	-	2.25%	1.28	-	1.58%
Volatility	81	-	83%	81	-	89%		88%
Dividend yield	None			None			None
Expected term (in years)		6.25		5.00	-	6.25		6.25