Note 12 - Equity Incentive Plan - Total Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Stock-based compensation expense	$ 2,240	$ 1,443	$ 2,033	$ 2,829
Cost of Sales [Member]
Stock-based compensation expense	216	82	362	174
Research and Development Expense [Member]
Stock-based compensation expense	156	91	352	268
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 1,868	$ 1,270	$ 1,319	$ 2,387