Note 8 - Stockholder's Equity - Stock-based Compensation (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Payment Arrangement, Expense	$ 253,000	$ 175,000	$ 459,000	$ 475,000
Cost of Sales [Member]
Share-based Payment Arrangement, Expense	1,000	3,000	2,000	9,000
Selling and Marketing Expense [Member]
Share-based Payment Arrangement, Expense	110,000	11,000	166,000	29,000
Research and Development Expense [Member]
Share-based Payment Arrangement, Expense	38,000	30,000	75,000	86,000
General and Administrative Expense [Member]
Share-based Payment Arrangement, Expense	$ 104,000	$ 131,000	$ 216,000	$ 351,000