Note 6 - Equity Incentive Plan (Tables)

9 Months Ended

Sep. 30, 2017

Notes Tables

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

	Nine Months Ended September 30,
	2017				2016
Risk-free interest rate		1.60%	-	1.78%		0.94%	-	1.40%
Expected volatility		41.36%	-	44.30%		48.84%	-	51.61%
Expected life (years)			4.0				4.5
Expected dividend yield			0.00%				0.00%

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

	Three Months Ended September 30,				Nine Months Ended September 30,
	2017		2016		2017		2016
Cost of product revenue	$	107	$	40	$	306	$	66
Research and development		177		156		340		300
Selling, general and administrative		1,190		601		3,294		1,910
Total stock-based compensation expense	$	1,474	$	797	$	3,940	$	2,276