Note 10 - Stockholders' Equity - Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock-based compensation	$ 3,022	$ 2,642	$ 2,349
Cost of Sales [Member]
Stock-based compensation	333	310	272
Sales [Member]
Stock-based compensation	516	544	529
General and Administrative Expense [Member]
Stock-based compensation	1,883	1,509	1,293
Research and Development Expense [Member]
Stock-based compensation	290	279	255
Share-based Payment Arrangement, Option [Member]
Stock-based compensation	1,938	1,580	1,457
Restricted Stock Units (RSUs) [Member]
Stock-based compensation	$ 1,084	$ 1,062	$ 892