Note 11 - Financial Information about Geographic Areas - Consolidated Net Sales and Long-lived Asset Information by Geographic Area (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Net sales by geographic region
Consolidated sales	$ 11,415,000	$ 12,109,000	$ 23,718,000	$ 23,551,000
Long-lived assets by geographic region
Consolidated long-lived assets	3,232,000		3,232,000		$ 3,244,000
Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	11,415,000
UNITED STATES
Long-lived assets by geographic region
Consolidated long-lived assets	2,474,000		2,474,000		2,528,000
UNITED STATES | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	11,158,000	11,861,000	23,197,000	23,059,000
International Member
Long-lived assets by geographic region
Consolidated long-lived assets	758,000		758,000		$ 716,000
International Member | Reportable Geographical Components [Member]
Net sales by geographic region
Consolidated sales	$ 257,000	$ 248,000	$ 521,000	$ 492,000