Note 13 - Share-based Compensation (Tables)

12 Months Ended

Dec. 31, 2017

Notes Tables

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

	Years ended December 31 ,
	201 7		201 6		201 5
Cost of goods sol d	$	140	$	14	$	4
Research and developmen t		678		127		29
Selling, general and administrativ e		1,889		801		250
Share-based compensation expens e	$	2,707	$	942	$	283

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

	Options outstanding
				Weighted		Weighted		Aggregate
				average		average		intrinsic
	Number of			exercise		remaining contractual		value
	shares			price		term (years)		(in thousands)
Balance, December 31, 2016		3,491,937		$	1.78		8.7	$	39,046
Stock options granted		842,653			7.66
Stock options exercised		( 87,542	)		1.87
Stock options cancelled		( 33,948	)		0.48
Balance, December 31, 2017		4,213,100		$	2.96		8.1	$	1,890
Exercisable, December 31, 2017		1,556,234		$	2.28		6.9	$	844
Unexercisable, December 31, 2017		2,656,866		$	3.36		8.8	$	1,046

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

			Weighte d
			averag e
			grant dat e
	Number o f		fair valu e
	share s		per shar e
Balance, December 31, 201 6		—
RSUs grante d		97,996	$	8.71
RSUs veste d		—
RSUs forfeite d		—
Balance, December 31, 201 7		97,996	$	8.71

Non-employee Stock Options [Member]

Notes Tables

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

	Years ended December 31 ,
	201 7			201 6			201 5
Risk-free interest rate	2.25	-	2.40%	1.60	-	2.42%	1.26	-	2.30%
Volatility	81	-	87%	89	-	91%	71	-	95%
Dividend yield		None			None			None
Expected term (in years)	8.6	-	9.8	9.6	-	9.9	8.5	-	9.7

Employee Stock Option [Member]

Notes Tables

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

	Years ended December 31 ,
	201 7			201 6
Risk-free interest rat e	1.76	-	2.25%	1.28	-	1.58%
Volatilit y	81	-	89%		88%
Dividend yiel d		None			None
Expected term (in years )	5.00	-	6.25		6.25