Note 7 - Share-based Compensation (Tables)

6 Months Ended

Jun. 30, 2018

Notes Tables

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

	Three months ended June 30,				Six months ended June 30,
	2018		2017		2018		2017
Cost of goods sold	$	36	$	33	$	66	$	74
Research and development		264		154		461		326
Selling, general and administrative		438		489		826		898
Share-based compensation expense	$	738	$	676	$	1,353	$	1,298

Share-based Compensation, Stock Options, Activity [Table Text Block]

				Weighted
				average
	Number of			exercise
	shares			price
Balance, December 31, 2017		4,213,100		$	2.96
Stock options granted		1,603,075			2.48
Stock options exercised		(2,488	)		1.80
Stock options cancelled		(135,487	)		2.69
Balance, June 30, 2018		5,678,200		$	2.83

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

				Weighted
				average
				grant date
	Number of			fair value
	shares			per share
Balance, December 31, 2017		97,996		$	8.71
RSUs vested		(57,108	)		7.03
Balance, June 30, 2018		40,888		$	11.04

Non-employee Stock Options [Member]

Notes Tables

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

Risk-free interest rate	2.80%	-	2.84%
Volatility	78%	-	80%
Dividend yield		None
Expected term (in years)	8.1	-	8.8

Employee Stock Option [Member]

Notes Tables

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

Risk-free interest rate	2.66%	-	2.87%
Volatility		81%
Dividend yield		None
Expected term (in years)		6.25