Note 11 - Shareholders' Equity - Stock-based Compensation Expense (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Total stock-based compensation expense	$ 812,000	$ 519,000
Per basic share (in dollars per share)	$ 0.06	$ 0.04
Per diluted share (in dollars per share)	$ 0.06	$ 0.04
Cost of Sales [Member]
Total stock-based compensation expense	$ 79	$ 1
Selling, General and Administrative Expenses [Member]
Total stock-based compensation expense	735,000	546,000
Research and Development Expense [Member]
Total stock-based compensation expense	$ (2,000)	$ (28,000)