Note 7 - Share-based Compensation (Tables)

3 Months Ended

Mar. 31, 2018

Notes Tables

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

	Three months ended March 31,
	2018		2017
Cost of goods sold	$	30	$	41
Research and development		197		172
Selling, general and administrative		388		409
Share-based compensation expense	$	615	$	622

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		1,429,075			2.60
Stock options exercised		(2,488	)		1.80
Stock options cancelled		(20,833	)		7.56
Balance, March 31, 2018		5,618,854		$	2.85

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 granted		—
RSUs vested		(20,444	)		11.04
RSUs forfeited		—
Balance, March 31, 2018		77,552		$	8.09

Non-employee Stock Options [Member]

Notes Tables

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

Risk-free interest rate		2.83%
Volatility		80%
Dividend yield		None
Expected term (in years)	8.4	-	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%
Volatility		81%
Dividend yield	None
Expected term (in years)		6.25%