Note 9 - Stockholders' Equity - Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Allocated Share-based Compensation Expense, Total	$ 2,349	$ 2,256	$ 1,680
Cost of Sales [Member]
Allocated Share-based Compensation Expense, Total	272	188	175
Sales [Member]
Allocated Share-based Compensation Expense, Total	529	403	373
General and Administrative Expense [Member]
Allocated Share-based Compensation Expense, Total	1,293	1,484	983
Research and Development Expense [Member]
Allocated Share-based Compensation Expense, Total	255	181	149
Employee Stock Option [Member]
Allocated Share-based Compensation Expense, Total	1,457	1,612	1,116
Restricted Stock Units (RSUs) [Member]
Allocated Share-based Compensation Expense, Total	$ 892	$ 644	$ 564