Note 11 - Financial Information about Geographic Areas - Consolidated Net Sales and Long-lived Asset Information by Geographic Area (Details) - USD ($)	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Net sales by geographic region
Consolidated sales	$ 12,304,000	$ 11,442,000
Long-lived assets by geographic region
Consolidated long-lived assets	3,271,000		$ 3,244,000
Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	12,304,000
UNITED STATES
Long-lived assets by geographic region
Consolidated long-lived assets	2,538,000		2,528,000
UNITED STATES | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	12,040,000	11,198,000
International Member
Long-lived assets by geographic region
Consolidated long-lived assets	733,000		$ 716,000
International Member | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	$ 264,000	$ 244,000