Note 11 - Financial Information about Geographic Areas - Consolidated Net Sales and Long-lived Asset Information by Geographic Area (Details) - Reportable Geographical Components [Member] - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Net sales by geographic region
Consolidated sales	$ 12,104,000	$ 12,049,000	$ 35,655,000	$ 34,082,000
Long-lived assets by geographic region
Consolidated long-lived assets	3,158,000		3,158,000		$ 3,158,000
UNITED STATES
Net sales by geographic region
Consolidated sales	11,918,000	11,739,000	34,977,000	33,469,000
Long-lived assets by geographic region
Consolidated long-lived assets	2,554,000		2,554,000		2,593,000
International Member
Net sales by geographic region
Consolidated sales	186,000	$ 310,000	678,000	$ 613,000
Long-lived assets by geographic region
Consolidated long-lived assets	$ 604,000		$ 604,000		$ 565,000