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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Net sales by geographic region
Consolidated sales	$ 12,109,000	$ 11,282,000	$ 23,551,000	$ 22,032,000
Long-lived assets by geographic region
Consolidated long-lived assets	3,111,000		3,111,000		$ 3,158,000
UNITED STATES
Net sales by geographic region
Consolidated sales	11,861,000	11,131,000	23,059,000	21,729,000
Long-lived assets by geographic region
Consolidated long-lived assets	2,581,000		2,581,000		2,593,000
International Member
Net sales by geographic region
Consolidated sales	248,000	$ 151,000	492,000	$ 303,000
Long-lived assets by geographic region
Consolidated long-lived assets	$ 530,000		$ 530,000		$ 565,000