Note 11 - Financial Information about Geographic Areas - Consolidated Net Sales and Long-lived Asset Information by Geographic Area (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Net sales by geographic region
Consolidated sales	$ 12,027,000	$ 12,104,000	$ 35,745,000	$ 35,655,000
Long-lived assets by geographic region
Consolidated long-lived assets	4,002,000		4,002,000		$ 3,244,000
Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	12,027,000
UNITED STATES
Long-lived assets by geographic region
Consolidated long-lived assets	3,240,000		3,240,000		2,528,000
UNITED STATES | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	11,806,000	11,918,000	35,004,000	34,977,000
International Member
Long-lived assets by geographic region
Consolidated long-lived assets	762,000		762,000		$ 716,000
International Member | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	$ 221,000	$ 186,000	$ 741,000	$ 678,000