Note 6 - Equity Incentive Plan - Total Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Stock-based compensation expense	$ 1,443	$ 1,322	$ 2,829	$ 8,887
Cost of Sales [Member]
Stock-based compensation expense	82	(28)	174	(244)
Research and Development Expense [Member]
Stock-based compensation expense	91	241	268	451
Selling, General and Administrative Expenses [Member]
Stock-based compensation expense	$ 1,270	$ 1,109	$ 2,387	$ 8,680