Note 9 - Stockholders' Equity - Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-based compensation	$ 2,642	$ 2,349	$ 2,256
Cost of Sales [Member]
Stock-based compensation	310	272	188
Sales [Member]
Stock-based compensation	544	529	403
General and Administrative Expense [Member]
Stock-based compensation	1,509	1,293	1,484
Research and Development Expense [Member]
Stock-based compensation	279	255	181
Share-based Payment Arrangement, Option [Member]
Stock-based compensation	1,580	1,457	1,612
Restricted Stock Units (RSUs) [Member]
Stock-based compensation	$ 1,062	$ 892	$ 644