Note 9 - Summary of Stock Options (Tables)

12 Months Ended

Dec. 31, 2016

Notes Tables

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

	Year Ended December 31, 2016
						Weighted
				Weighted		Average		Aggregate
	Number			Average		Remaining		Intrinsic
	of			Exercise		Contractual		Value
	Shares			Price		Term (years)		(in thousands)
Options outstanding, beginning of period		1,022,195		$	6.47		9.37	$	1,194,180
Options granted		978,966		$	6.00
Options exercised		(3,020	)	$	4.80
Options canceled		(88,377	)	$	7.41
Options outstanding, end of period		1,909,764		$	6.19		9.12	$	211,396
Vested and exercisable and expected to vest, end of period		1,761,430		$	6.22		9.09	$	204,619
Vested and exercisable, end of period		368,681		$	7.51		8.04	$	102,306

Schedule of Share-based Compensation, Shares Authorized under Stock Option Plans, by Exercise Price Range [Table Text Block]

			Options Outstanding						Options Exercisable
							Weighted
			Number		Weighted		Average		Number		Weighted
			Outstanding		Average		Remaining		Exercisable		Average
Range of			as of		Exercise		Contractual		as of		Exercise
Exercise Prices			December 31, 2016		Price		Term (Years)		December 31, 2016		Price
	$2.64			12,500	$	2.64		8.37		5,209	$	2.64
$3.68	-	$3.76		79,376	$	3.75		8.10		36,382	$	3.75
$4.80	-	$4.92		197,969	$	4.80		7.80		109,150	$	4.80
	$5.22			595,034	$	5.22		9.98		7,250	$	5.22
	$6.00			565,628	$	6.00		8.96		141,412	$	6.00
$6.24	-	$6.40		129,267	$	6.35		9.15		-	$	-
$7.00	-	$7.92		284,075	$	7.71		9.49		23,363	$	7.72
	$9.92			38,135	$	9.92		5.89		38,135	$	9.92
$56.00	-	$296.00		7,780	$	83.66		0.83		7,780	$	83.66
				1,909,764	$	6.19		9.12		368,681	$	7.51

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

	Year Ended
	December 31,
	2016			2015
Expected term (in years)		5			5
Average volatility		49	%		63	%
Risk-free interest rate		1.78	%		1.70	%
Dividend yield		0	%		0	%

	Year Ended
	December 31,
	2016
Expected term (in years)		10
Average volatility		51	%
Risk-free interest rate		2.43	%
Dividend yield		0	%

Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block]

	Year Ended
	December 31,
	2016		2015
Research and development	$	114	$	18
Selling, general and administrative		867		202
Total	$	981	$	220