Note 12 - Stockholders' Equity - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Stock-based compensation expense	$ 619	$ 554	$ 1,298	$ 1,510
Cost of Sales [Member]
Stock-based compensation expense	16	22	47	44
Research and Development Expense [Member]
Stock-based compensation expense	11	15	53	120
General and Administrative Expense [Member]
Stock-based compensation expense	$ 592	$ 517	$ 1,198	$ 1,346