Note 7 - Stockholders' Equity - Stock-based Compensation (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Stock-based compensation	$ 234,000	$ 253,000	$ 615,000	$ 459,000
Cost of Sales [Member]
Stock-based compensation	3,000	1,000	5,000	2,000
Selling and Marketing Expense [Member]
Stock-based compensation	65,000	110,000	106,000	166,000
Research and Development Expense [Member]
Stock-based compensation	36,000	38,000	72,000	75,000
General and Administrative Expense [Member]
Stock-based compensation	$ 130,000	$ 104,000	$ 432,000	$ 216,000