Note 6 - Stockholders' Equity, Stock Plans and Stock-based Compensation Expense - Stock-based Compensation Expense by Department (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allocated share-based compensation expense	$ 9,832	$ 7,157	$ 5,110
Cost of Sales [Member]
Allocated share-based compensation expense	1,572	743	660
Selling and Marketing Expense [Member]
Allocated share-based compensation expense	4,510	2,105	1,642
Research and Development Expense [Member]
Allocated share-based compensation expense	1,536	824	936
General and Administrative Expense [Member]
Allocated share-based compensation expense	$ 2,214	$ 3,485	$ 1,872